Soybean aphid
Encyclopedia
The soybean aphid is an insect
pest of soybean
(Glycine max (L.) Merr.) that is exotic to North America
. The soybean aphid is native to Asia
. It has been described as a common pest of soybean
s in China
and as an occasional pest of soybeans in Indonesia
, Japan
, Korea
, Malaysia, the Philippines
, and Thailand
. The soybean aphid was first documented in North America in Wisconsin
in July 2000. Ragsdale et al. (2004) noted that the soybean aphid probably arrived in North America earlier than 2000, but remained undetected for a period of time. Venette and Ragsdale (2004) suggested that Japan probably served as the point of origin for the soybean aphid’s North American invasion. By 2003, the soybean aphid had been documented in Delaware
, Georgia
, Illinois
, Indiana
, Iowa
, Kansas
, Kentucky
, Michigan
, Minnesota
, Mississippi
, Missouri
, Nebraska
, New York
, North Dakota
, Ohio
, Pennsylvania
, South Dakota
, Virginia
, West Virginia
, and Wisconsin
. Together, these states accounted for 89% of the 63600000 acres (257,380.3 km²) of soybean planted in the United States
in 2007.
holocyclic life cycle
, which means the insect
alternates hosts and undergoes sexual reproduction
for at least part of its life cycle. Soybean aphids overwinter
as eggs on their primary hosts, buckthorn
(Rhamnus spp.). Eggs can be located near buds or within crevices of branches. With a mean supercooling
point of -34 °C, eggs are well-adapted for surviving cold winters.
In two studies, the quantity of overwintering eggs had a strong positive correlation with the severity of soybean aphid outbreak
s in the following spring.
Eggs begin to hatch into fundatrices when temperatures in the spring reach 10 °C (50 °F). Colonization of buckthorn
by soybean aphids in the spring can lead to curling of leaves and twigs. Near the blooming stage of buckthorn
, fundatrices reproduce parthenogenetically to give viviparous birth to alatae. These winged soybean aphids begin the spring migration to their secondary host, soybean
. Soybean aphids go through approximately 15 generations on soybean, all of which are primarily composed of apterous females produced through viviparous parthenogenesis. Each generation passes through 4 instar
s and can range from 2 to 16 days in length, with lower temperatures increasing development and decreasing generation time.
Feeding by soybean aphids injures soybean
by interfering with photosynthetic pathways—more specifically, biological mechanisms responsible for restoring chlorophyll
to a low energy state are impaired. This restoration process is known as quenching and is important for plants to execute light reactions properly. Reduction in photosynthetic capacity of soybean may occur before plants begin to display symptom
s of injury.
Infestation of soybean aphids on soybean can be classified into three stages. The first stage occurs when alatae migrate to soybean in late May and early June. During this stage, small colonies of soybean aphids appear patchy, occurring on single plants scattered throughout a field. In these early colonies, soybean aphids are typically grouped on tender, young leaves of soybean plants. As the infested plant ages, soybean aphids remain on leaves near the top of the plant. Studies have demonstrated a positive correlation
exists between upper leaf nitrogen
content of soybean and the occurrence of soybean aphids. Damage to a soybean plant during this initial stage is a result of stylet
-feeding and can include curling and stunting of leaves and twigs, physiological delays, and underdevelopment of root
tissue. However, the relatively low densities of soybean aphids during this stage have been found to have minimal impacts on soybean yield
.
The second stage, or pre-peak stage, can begin as early as late June and is characterized by dramatic increases in densities of soybean aphids. As colonies expand and temperatures increase, soybean aphids move toward lower portions of the soybean plant. The optimal temperature for soybean aphid development occurs between 25 and 30 °C, and exposure to prolonged temperatures of 35 °C (95 °F) decrease survival rate
s and fecundity
of soybean aphids. Extremely high population growth rates can be achieved under optimal conditions, with a colony doubling in size in as few as 1.3 days.
The final stage of infestation by soybean aphids on soybean, or peak stage, begins in mid- to late July and is characterized by very high densities of soybean aphids. As populations grow during this stage, plant damage may become severe. Heavy infestations of soybean aphids may cause plant stunting, distorted foliage, premature defoliation, stunted stems and leaves, reduced branch, pod, and seed numbers, lower seed weight, and underdevelopment of root tissue. Yield losses as high as 50 to 70% have been documented as a result of prolonged exposure to high densities of soybean aphids.
When populations of soybean aphids increase, a need arises for apterae to produce alate
offspring to seek out new hosts. This can be due to both deteriorating host plant quality and crowding effects. Crowding of nymph
al apterae will not cause them to develop into alate adults. Crowding effects on alatae can induce alate offspring production as well, although alatae are not as sensitive to crowding as apterae. Soybean plants are prevented from becoming super-saturated by emigration
of soybean aphids through alate production, which serves to maintain an equilibrium density of soybean aphids. Decreased body size and lowered fecundity can be induced in soybean aphids when populations reach very high densities.
As host plant quality begins to deteriorate in late August and early September, soybean aphids take on a paler color and experience decreased growth and reproductive rates. High densities of soybean aphids during these late plant stages have less of a significant negative impact on soybean yield. During this period of declining temperatures and decreasing rainfall, soybean plants undergo senescence
gradually from bottom to top, causing an upward movement of soybean aphids to higher plant tissue.
After going through approximately 15 generations on soybean, soybean aphids begin to transition back to their primary host, buckthorn. A generation of winged females, gynoparae, develop on soybean and leave for buckthorn when mature. Simultaneously, an apterous population of soybean aphids remains on soybean to produce alate male sexual morph
s. Factors that positively affect the production of gynoparae and male alatae include declining host plant quality, shortened day length, and lowered temperatures.
While on buckthorn, gynoparae produce a generation of apterous female sexual morphs (oviparae) that mate with male alatae to produce overwintering eggs. As buckthorn experiences increased feeding pressure by oviparae, volatile
emissions from the plant are significantly decreased, possibly serving as a defense mechanism to inhibit further colonization by soybean aphids. Male alatae locate oviparae on buckthorn through two sex pheromone
s commonly found in aphid species, (1R,4aS,7S,7aR)-nepetalactol and (4aS,7S,7aR)-nepetalactone, that are emitted by oviparae in a species-specific combination. After mating on buckthorn, oviparae deposit their eggs on the plant. Ragsdale et al. (2004) proposed that movement from soybean to buckthorn may produce a bottleneck
effect that inhibits the ability of soybean aphids to overwinter in great numbers.
More than 100 species
of Rhamnus exist worldwide, and most of these species are native to temperate
regions of the Northern Hemisphere
. Rhamnus species are plentiful in North America
. Two confirmed Rhamnus species that support overwinter
ing of soybean aphids in North America are common buckthorn
(Rhamnus cathartica) of exotic origin and alderleaf buckthorn
(Rhamnus alnifolia) of native origin. Another widespread Rhamnus species
of exotic origin in North America
is alder buckthorn
(Rhamnus frangula); however, neither mature oviparae nor eggs have been documented on this potential host.
In an experiment to determine alternate primary hosts for soybean aphids, only members of the genus Rhamnus were able to support development of soybean aphids. In Asia
, where the soybean aphid is native, dominant primary hosts include Japanese buckthorn (Rhamnus japonica) and Dahurian buckthorn (Rhamnus davurica). One study indicated certain plant species may play a role in bridging colonization of soybean
from buckthorn. One such species
that is readily available in early spring is red clover
(Trifolium pratense). An experiment further reinforced this relationship by demonstrating that soybean aphids can develop on red clover in a laboratory setting.
The most common secondary host in both Asia and North America for soybean aphids is soybean. Soybean has been cultivated in Asia for 4,000 to 5,000 years and in the United States
since 1904. Du et al. (1994) demonstrated that the primary method by which soybean aphids locate soybean is through olfactory chemical signaling. Interference by non-host odors diminished the ability of soybean aphids to locate and colonize soybean.
Deleterious effects of soybean aphids on soybean can be highly variable and are influenced by factors like soybean aphid density, plant stage, plant density, and temperature. In addition, soil nutrient
conditions within a soybean field may play some role in the development of infestation
s of soybean aphids. For example, in a laboratory experiment, soybean aphids that fed on potassium
-deficient soybean experienced increased fecundity
and survivorship. Field experiments failed to corroborate this finding. Myers et al. (2005a) hypothesized that potassium-stress in the laboratory may lead to increased nitrogen
availability for soybean aphids. Yield data taken from this experiment showed that potassium-stress in conjunction with infestation by soybean aphids caused significant yield loss.
Specificity for soybean aphids to feed on soybean has been demonstrated by Han and Yan (1995) in an experiment utilizing an electrical penetration graph. While no difference in the amount of time spent probing between soybean and other non-host plants was observed, the ingestion of phloem
by soybean aphids was either greatly reduced or did not happen at all on non-host plants. Nevertheless, some alternate secondary hosts have been observed for soybean aphids. The most widespread of these alternate secondary hosts is wild soybean
(Glycine soja), which has been known to support colonies of soybean aphids in Asia. In Korea
and the Philippines
, kudzu
(Pueraria montana) and tropical kudzu (Pueraria javanica) have been described as alternate secondary hosts, respectively.
penetration. Non-persistent transmission does not limit viruses vectored by soybean aphids to soybean, but rather to any plant that alate
soybean aphids contact and probe with their stylets for a brief period of time. Unlike stationary apterae, only alatae have been shown to transmit viruses between plants. Incidence of non-persistently transmitted viruses has been shown to increase when flight activity of the vector is high, leading to the belief that the risk of virus transmission by soybean aphids may increase during times of high dispersal, such as the end of the peak stage.
In China
, the most important virus vectored by the soybean aphid is Soybean mosaic virus
, which can cause yield loss and decreased seed quality. This virus is also found in North America
and has been demonstrated as being vectored by the soybean aphid in field studies. In addition to Soybean mosaic virus, the soybean aphid is capable of transmitting Soybean stunt virus, Soybean dwarf virus
, Abaca mosaic virus, Alfalfa mosaic virus
, Beet mosaic virus
, Tobacco vein-banding virus, Tobacco ringspot virus
, Bean yellow mosaic virus
, Mungbean mosaic virus, Peanut mottle virus
, Peanut stripe poty virus, and Peanut mosaic virus.
have demonstrated resistance
to the soybean aphid. Resistance may be conferred by antibiosis
, antixenosis, or tolerance
. In some instances, such as with the soybean cultivars 'Dowling', 'Jackson', and 'Palmetto', resistance to the soybean aphid results from a combination of both antibiosis and antixenosis. In the 'Dowling' cultivar, resistance is conferred by a single dominant gene
(Rag1). Soybean plants that are resistant to the soybean aphid can cause both reduced fecundity
and longevity
in soybean aphids. In the case of antibiosis, certain life stages of the soybean aphid may be more susceptible than others. For example, nymphs have higher rates of metabolism
than other life stages, ingest more phloem
, and are thus exposed to larger quantities of antibiotic compounds. Expression of antibiotic factors in resistant soybean plants that negatively affect soybean aphids has been shown to remain constant throughout the growing season, remaining unaffected by the physiological maturity of the plant. Colonization of resistant soybean cultivars can vary between years depending upon the level of infestation, with resistant plants showing lower levels of resistance in years with significant levels of soybean aphid infestation. Physical characteristics of soybean, such as dense pubescence, have thus far proven incapable of reducing colonization by soybean aphids.
In Asia
, the soybean aphid experiences pressure from over 30 species of predators, 8 species of parasitoids, and some fungal pathogens. In Indonesia
, where the soybean aphid is considered an occasional pest, evidence indicates the use of insecticides to control soybean aphids may not always be necessary due to suppression of the insect to subeconomic densities by natural enemies alone. In North America
, the dominant natural enemies in soybean
are generalist predators. Exclusion cage experiments have provided evidence that predators can play an important role in suppression of the soybean aphid. Impacts from predators include both the ability to suppress colony establishment early in the season as well as respond to increased densities of soybean aphids late in the season.
One of the most important predators of soybean aphids in North America is the insidious flower bug (Orius insidiosus (Say)). The insidious flower bug has its greatest impact on early to mid-season populations of soybean aphids and is often able to keep soybean aphid densities low. Fox et al. (2004) hypothesized that the impact from this predator early in the season could be attributed to small plant size and sparse canopies, which aid the insidious flower bug by reducing foraging
time and decreasing the number of places soybean aphids can hide (i.e., enemy-free space). In addition, synomones released by soybean after being colonized by soybean aphids may aid the insidious flower bug in host location. When populations of soybean aphids reach very high densities, top-down pressure exerted by the insidious flower bug may fail to suppress colony growth of soybean aphids.
Another group of predators that plays a key role in suppression of populations of soybean aphids in North America is lady beetles (Coccinellidae spp.). Some prevalent species in soybean include the twospotted lady beetle (Adalia bipunctata L.), the sevenspotted lady beetle
(Coccinella septempunctata L.), the spotted lady beetle
(Coleomegilla maculata De Geer), the polished lady beetle (Cycloneda munda (Say)), the multicolored Asian lady beetle (Harmonia axyridis (Pallas)), the convergent lady beetle
(Hippodamia convergens Guérin-Méneville), and the thirteen spotted lady beetle (Hippodamia tredecimpunctata L.).
Evidence suggests that populations of lady beetles can respond to increases in populations of soybean aphids in soybean. In addition, increases in populations of lady beetles have the ability to inhibit colony growth of soybean aphids throughout the growing season. As generalist
predators, lady beetles are able to feed on alternate prey when soybean aphids are at low densities. Other characteristics of lady beetles that are advantageous in times of soybean aphid scarcity include developmental delays of certain life stages, decreased body weights, and reduced clutch
sizes. One of the most competitive lady beetles in North America, the multicolored Asian lady beetle, is of exotic origin. When soybean aphids are plentiful, an adult multicolored Asian lady beetle has the capacity to consume 160 soybean aphids per day.
Other foliar-foraging predators that are present North American soybean fields that may play a role in suppression of soybean aphid populations include green lacewings (Chrysoperla spp.), brown lacewings (Hemerobius spp.), damsel bugs (Nabis spp.), big eyed bugs (Geocoris spp.), spined soldier bug
s (Podisus maculiventris (Say)), hover flies (Syrphidae spp.), and the aphid midge (Aphidoletes aphidimyza (Rondani)). Another group of predators that are present in soybean fields is ground beetle
s (Carabidae spp.); however, field experiments have shown limited to no impact from these predators on populations of soybean aphids due to the fact that ground beetles rarely scale soybean plants for prey. While parasitoids of the soybean aphid have a large impact on colonies in Asia—Lysiphlebia japonica (Ashmead) can have a soybean aphid parasitism rate as high as 52.6% in China
—parasitoids are thought to exert only minimal pressure on soybean aphids in North America.
. Insecticides available to soybean producers for controlling soybean aphids include both foliar-applied treatments and seed-applied treatments. Although seed-applied treatments have proven to be a convenient delivery method for insect control, studies have experienced inconsistent results regarding their efficacy
against the soybean aphid. Management decisions should be made with an understanding of soybean aphid life history and sound scouting practices rooted in the principles of integrated pest management
.
The current economic threshold
for soybean aphids states that an insecticide application is warranted when soybean aphid densities reach 250 soybean aphids per plant, 80% of sampled plants are infested, the population is currently increasing, and few natural enemies are observed in the field. This recommendation is only valid from the R1 (beginning bloom) to R5 (beginning seed) growth stages and is based on an economic injury level of 674 soybean aphids per plant. Due to the clumped spatial distribution of soybean aphids, Onstad et al. (2005) recommend that 50 plants should be sampled within a field to attain an accurate representation of densities of soybean aphids. Soybean producers can choose from a variety of foliar insecticides from the carbamate
, pyrethroid
, and organophosphate
chemical families to control soybean aphids.
Evidence indicates that foliar insecticide applications can reduce symptoms associated with soybean aphid infestations, including curled leaves, shortened stems, stunted plants, and premature defoliation. Foliar insecticide applications can also prevent yield loss associated with high densities of soybean aphids. However, some risks are associated with the use of foliar insecticide applications, especially if integrated pest management principles are abandoned. A single, well-timed application may not sufficiently control soybean aphids and prevent yield loss, especially if large quantities of soybean aphids are surviving on lower leaves. Foliar insecticide applications can work detrimentally if nontarget effects are experienced, such as the unintended death of beneficial natural enemies.
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
pest of soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
(Glycine max (L.) Merr.) that is exotic to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. The soybean aphid is native to Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
. It has been described as a common pest of soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
s in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and as an occasional pest of soybeans in Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
, Malaysia, the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, and Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
. The soybean aphid was first documented in North America in Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
in July 2000. Ragsdale et al. (2004) noted that the soybean aphid probably arrived in North America earlier than 2000, but remained undetected for a period of time. Venette and Ragsdale (2004) suggested that Japan probably served as the point of origin for the soybean aphid’s North American invasion. By 2003, the soybean aphid had been documented in Delaware
Delaware
Delaware is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, and to the north by Pennsylvania...
, Georgia
Georgia (U.S. state)
Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...
, Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
, Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...
, Iowa
Iowa
Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...
, Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
, Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
, Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
, Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
, Mississippi
Mississippi
Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...
, Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
, Nebraska
Nebraska
Nebraska is a state on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha, on the Missouri River....
, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
, Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
, South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...
, and Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
. Together, these states accounted for 89% of the 63600000 acres (257,380.3 km²) of soybean planted in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
in 2007.
Life history
The soybean aphid possesses a heteroeciousHeteroecious
A heteroecious parasite is one that requires at least two hosts. The primary host is the host in which the parasite spends its adult life; the other is the secondary host. Both the primary host and an unrelated alternate host are required for the parasite to complete its life cycle...
holocyclic life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
, which means the insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
alternates hosts and undergoes sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
for at least part of its life cycle. Soybean aphids overwinter
Overwinter
To overwinter is to pass through or wait out the winter season, or to pass through that period of the year when “winter” conditions make normal activity or even survival difficult or near impossible...
as eggs on their primary hosts, buckthorn
Buckthorn
The Buckthorns are a genus of about 100 species of shrubs or small trees from 1-10 m tall , in the buckthorn family Rhamnaceae...
(Rhamnus spp.). Eggs can be located near buds or within crevices of branches. With a mean supercooling
Supercooling
Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid....
point of -34 °C, eggs are well-adapted for surviving cold winters.
In two studies, the quantity of overwintering eggs had a strong positive correlation with the severity of soybean aphid outbreak
Outbreak
Outbreak is a term used in epidemiology to describe an occurrence of disease greater than would otherwise be expected at a particular time and place. It may affect a small and localized group or impact upon thousands of people across an entire continent. Two linked cases of a rare infectious...
s in the following spring.
Eggs begin to hatch into fundatrices when temperatures in the spring reach 10 °C (50 °F). Colonization of buckthorn
Buckthorn
The Buckthorns are a genus of about 100 species of shrubs or small trees from 1-10 m tall , in the buckthorn family Rhamnaceae...
by soybean aphids in the spring can lead to curling of leaves and twigs. Near the blooming stage of buckthorn
Buckthorn
The Buckthorns are a genus of about 100 species of shrubs or small trees from 1-10 m tall , in the buckthorn family Rhamnaceae...
, fundatrices reproduce parthenogenetically to give viviparous birth to alatae. These winged soybean aphids begin the spring migration to their secondary host, soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
. Soybean aphids go through approximately 15 generations on soybean, all of which are primarily composed of apterous females produced through viviparous parthenogenesis. Each generation passes through 4 instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
s and can range from 2 to 16 days in length, with lower temperatures increasing development and decreasing generation time.
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
by interfering with photosynthetic pathways—more specifically, biological mechanisms responsible for restoring chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
to a low energy state are impaired. This restoration process is known as quenching and is important for plants to execute light reactions properly. Reduction in photosynthetic capacity of soybean may occur before plants begin to display symptom
Symptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
s of injury.
Infestation of soybean aphids on soybean can be classified into three stages. The first stage occurs when alatae migrate to soybean in late May and early June. During this stage, small colonies of soybean aphids appear patchy, occurring on single plants scattered throughout a field. In these early colonies, soybean aphids are typically grouped on tender, young leaves of soybean plants. As the infested plant ages, soybean aphids remain on leaves near the top of the plant. Studies have demonstrated a positive correlation
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
exists between upper leaf nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
content of soybean and the occurrence of soybean aphids. Damage to a soybean plant during this initial stage is a result of stylet
Stylet
A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...
-feeding and can include curling and stunting of leaves and twigs, physiological delays, and underdevelopment of root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
tissue. However, the relatively low densities of soybean aphids during this stage have been found to have minimal impacts on soybean yield
Crop yield
In agriculture, crop yield is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself...
.
The second stage, or pre-peak stage, can begin as early as late June and is characterized by dramatic increases in densities of soybean aphids. As colonies expand and temperatures increase, soybean aphids move toward lower portions of the soybean plant. The optimal temperature for soybean aphid development occurs between 25 and 30 °C, and exposure to prolonged temperatures of 35 °C (95 °F) decrease survival rate
Survival rate
In biostatistics, survival rate is a part of survival analysis, indicating the percentage of people in a study or treatment group who are alive for a given period of time after diagnosis...
s and fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
of soybean aphids. Extremely high population growth rates can be achieved under optimal conditions, with a colony doubling in size in as few as 1.3 days.
The final stage of infestation by soybean aphids on soybean, or peak stage, begins in mid- to late July and is characterized by very high densities of soybean aphids. As populations grow during this stage, plant damage may become severe. Heavy infestations of soybean aphids may cause plant stunting, distorted foliage, premature defoliation, stunted stems and leaves, reduced branch, pod, and seed numbers, lower seed weight, and underdevelopment of root tissue. Yield losses as high as 50 to 70% have been documented as a result of prolonged exposure to high densities of soybean aphids.
When populations of soybean aphids increase, a need arises for apterae to produce alate
Alate
An alate is a winged reproductive of a social insect . Alate females are typically those destined to become queens , whereas alate males are occasionally referred to as "drones"...
offspring to seek out new hosts. This can be due to both deteriorating host plant quality and crowding effects. Crowding of nymph
Nymph
A nymph in Greek mythology is a female minor nature deity typically associated with a particular location or landform. Different from gods, nymphs are generally regarded as divine spirits who animate nature, and are usually depicted as beautiful, young nubile maidens who love to dance and sing;...
al apterae will not cause them to develop into alate adults. Crowding effects on alatae can induce alate offspring production as well, although alatae are not as sensitive to crowding as apterae. Soybean plants are prevented from becoming super-saturated by emigration
Emigration
Emigration is the act of leaving one's country or region to settle in another. It is the same as immigration but from the perspective of the country of origin. Human movement before the establishment of political boundaries or within one state is termed migration. There are many reasons why people...
of soybean aphids through alate production, which serves to maintain an equilibrium density of soybean aphids. Decreased body size and lowered fecundity can be induced in soybean aphids when populations reach very high densities.
As host plant quality begins to deteriorate in late August and early September, soybean aphids take on a paler color and experience decreased growth and reproductive rates. High densities of soybean aphids during these late plant stages have less of a significant negative impact on soybean yield. During this period of declining temperatures and decreasing rainfall, soybean plants undergo senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
gradually from bottom to top, causing an upward movement of soybean aphids to higher plant tissue.
After going through approximately 15 generations on soybean, soybean aphids begin to transition back to their primary host, buckthorn. A generation of winged females, gynoparae, develop on soybean and leave for buckthorn when mature. Simultaneously, an apterous population of soybean aphids remains on soybean to produce alate male sexual morph
Morph
- Astronomy :* Morphs collaboration, a collaboration that studied the evolution of spiral galaxies using the Magellan and the Hubble Space Telescope- Biology :...
s. Factors that positively affect the production of gynoparae and male alatae include declining host plant quality, shortened day length, and lowered temperatures.
While on buckthorn, gynoparae produce a generation of apterous female sexual morphs (oviparae) that mate with male alatae to produce overwintering eggs. As buckthorn experiences increased feeding pressure by oviparae, volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
emissions from the plant are significantly decreased, possibly serving as a defense mechanism to inhibit further colonization by soybean aphids. Male alatae locate oviparae on buckthorn through two sex pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
s commonly found in aphid species, (1R,4aS,7S,7aR)-nepetalactol and (4aS,7S,7aR)-nepetalactone, that are emitted by oviparae in a species-specific combination. After mating on buckthorn, oviparae deposit their eggs on the plant. Ragsdale et al. (2004) proposed that movement from soybean to buckthorn may produce a bottleneck
Bottleneck
A bottleneck is a phenomenon where the performance or capacity of an entire system is limited by a single or limited number of components or resources. The term bottleneck is taken from the 'assets are water' metaphor. As water is poured out of a bottle, the rate of outflow is limited by the width...
effect that inhibits the ability of soybean aphids to overwinter in great numbers.
Host plant biology
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of Rhamnus exist worldwide, and most of these species are native to temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
regions of the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
. Rhamnus species are plentiful in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Two confirmed Rhamnus species that support overwinter
Overwinter
To overwinter is to pass through or wait out the winter season, or to pass through that period of the year when “winter” conditions make normal activity or even survival difficult or near impossible...
ing of soybean aphids in North America are common buckthorn
Rhamnus cathartica
Rhamnus cathartica , is a species in the family Rhamnaceae, native to Europe, northwest Africa, and western Asia, from the central British Isles south to Morocco, and east to Kyrgyzstan...
(Rhamnus cathartica) of exotic origin and alderleaf buckthorn
Rhamnus alnifolia
Rhamnus alnifolia is a species of flowering plant in the buckthorn family known by the common name alder buckthorn, or alderleaf buckthorn. It is native to North America, where it is known mainly from the southern half of Canada and the northern half of the United States and California...
(Rhamnus alnifolia) of native origin. Another widespread Rhamnus species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of exotic origin in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
is alder buckthorn
Rhamnus frangula
Frangula alnus, syn. Rhamnus frangula, the Alder Buckthorn, is a tall deciduous shrub in the family Rhamnaceae. It is native to Europe, northernmost Africa, and western Asia, from Ireland and Great Britain north to 68°N in Scandinavia, east to central Siberia and Xinjiang in western China, and...
(Rhamnus frangula); however, neither mature oviparae nor eggs have been documented on this potential host.
In an experiment to determine alternate primary hosts for soybean aphids, only members of the genus Rhamnus were able to support development of soybean aphids. In Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, where the soybean aphid is native, dominant primary hosts include Japanese buckthorn (Rhamnus japonica) and Dahurian buckthorn (Rhamnus davurica). One study indicated certain plant species may play a role in bridging colonization of soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
from buckthorn. One such species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
that is readily available in early spring is red clover
Red clover
Trifolium pratense is a species of clover, native to Europe, Western Asia and northwest Africa, but planted and naturalised in many other regions....
(Trifolium pratense). An experiment further reinforced this relationship by demonstrating that soybean aphids can develop on red clover in a laboratory setting.
The most common secondary host in both Asia and North America for soybean aphids is soybean. Soybean has been cultivated in Asia for 4,000 to 5,000 years and in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
since 1904. Du et al. (1994) demonstrated that the primary method by which soybean aphids locate soybean is through olfactory chemical signaling. Interference by non-host odors diminished the ability of soybean aphids to locate and colonize soybean.
Deleterious effects of soybean aphids on soybean can be highly variable and are influenced by factors like soybean aphid density, plant stage, plant density, and temperature. In addition, soil nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
conditions within a soybean field may play some role in the development of infestation
Infestation
Infestation refers to the state of being invaded or overrun by pests or parasites. It can also refer to the actual organisms living on or within a host.-Terminology:...
s of soybean aphids. For example, in a laboratory experiment, soybean aphids that fed on potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
-deficient soybean experienced increased fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
and survivorship. Field experiments failed to corroborate this finding. Myers et al. (2005a) hypothesized that potassium-stress in the laboratory may lead to increased nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
availability for soybean aphids. Yield data taken from this experiment showed that potassium-stress in conjunction with infestation by soybean aphids caused significant yield loss.
Specificity for soybean aphids to feed on soybean has been demonstrated by Han and Yan (1995) in an experiment utilizing an electrical penetration graph. While no difference in the amount of time spent probing between soybean and other non-host plants was observed, the ingestion of phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
by soybean aphids was either greatly reduced or did not happen at all on non-host plants. Nevertheless, some alternate secondary hosts have been observed for soybean aphids. The most widespread of these alternate secondary hosts is wild soybean
Glycine soja
Glycine soja, or wild soybean is an annual plant in the legume family. It is the wild ancestor of soybean, an important crop.-External links:***...
(Glycine soja), which has been known to support colonies of soybean aphids in Asia. In Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...
and the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, kudzu
Kudzu
Kudzu is a plant in the genus Pueraria in the pea family Fabaceae, subfamily Faboideae. It is a climbing, coiling, and trailing vine native to southern Japan and southeast China. Its name comes from the Japanese name for the plant, . It is a weed that climbs over trees or shrubs and grows so...
(Pueraria montana) and tropical kudzu (Pueraria javanica) have been described as alternate secondary hosts, respectively.
Virus transmission
Soybean aphids may indirectly affect plant health through viral transmission. Viruses spread by soybean aphids are typically vectored non-persistently, which allows for disease transmission in the first moments of styletStylet
A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...
penetration. Non-persistent transmission does not limit viruses vectored by soybean aphids to soybean, but rather to any plant that alate
Alate
An alate is a winged reproductive of a social insect . Alate females are typically those destined to become queens , whereas alate males are occasionally referred to as "drones"...
soybean aphids contact and probe with their stylets for a brief period of time. Unlike stationary apterae, only alatae have been shown to transmit viruses between plants. Incidence of non-persistently transmitted viruses has been shown to increase when flight activity of the vector is high, leading to the belief that the risk of virus transmission by soybean aphids may increase during times of high dispersal, such as the end of the peak stage.
In China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, the most important virus vectored by the soybean aphid is Soybean mosaic virus
Soybean mosaic virus
Soybean mosaic virus is a plant pathogenic virus of the family Potyviridae.Symptoms:Soybean mosaic causes stunting of plants and crinkled and mottling of leaves.Infected plants range from no symptoms to severely mottled and deformed....
, which can cause yield loss and decreased seed quality. This virus is also found in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and has been demonstrated as being vectored by the soybean aphid in field studies. In addition to Soybean mosaic virus, the soybean aphid is capable of transmitting Soybean stunt virus, Soybean dwarf virus
Soybean dwarf virus
Soybean dwarf virus is a pathogenic plant virus.-External links:**...
, Abaca mosaic virus, Alfalfa mosaic virus
Alfalfa mosaic virus
Alfalfa mosaic virus , also known as Lucerne mosaic virus or Potato calico virus, is a worldwide distributed phytopathogen that can lead to necrosis and yellow mosaics on a large variety of plant species, including commercially important crops. It is the only Alfamovirus of the Bromoviridae...
, Beet mosaic virus
Beet mosaic virus
Beet mosaic virus is a plant pathogenic virus of the family Potyviridae.-External links:**...
, Tobacco vein-banding virus, Tobacco ringspot virus
Tobacco ringspot virus
Tobacco ringspot virus is a plant pathogenic virus in the plant virus family Comoviridae. It is the type species of the Comoviridae Genus Nepovirus. Nepoviruses are be transmitted between plants by nematodes...
, Bean yellow mosaic virus
Bean yellow mosaic virus
Bean yellow mosaic virus is a plant pathogenic virus in the genus Potyvirus and the virus family Potyviridae. Like other members of the Potyvirus genus, BYMV is a monopartite strand of positive-sense, single-stranded RNA surrounded by a capsid made for a single viral encoded protein. The virus...
, Mungbean mosaic virus, Peanut mottle virus
Peanut mottle virus
Peanut mottle virus ' is a plant pathogenic virus of the family Potyviridae. As with other members of this virus family, PeMoV is a flexuous filamentous virus with particles 740-750 nm long. It is transmitted by several species of aphids and by mechanical inoculation...
, Peanut stripe poty virus, and Peanut mosaic virus.
Host plant resistance
Several varieties of soybeanSoybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
have demonstrated resistance
Plant disease resistance
Plant disease resistance is crucial to the reliable production of food, and it provides significant reductions in agricultural use of fuel, land, water and other inputs. There are numerous examples of devastating plant disease impacts , as well as recurrent severe plant disease issues...
to the soybean aphid. Resistance may be conferred by antibiosis
Antibiosis
Antibiosis is a biological interaction between two or more organisms that is detrimental to at least one of them or an antagonistic association between an organism and the metabolic substances produced by another....
, antixenosis, or tolerance
Physiological tolerance
Physiological tolerance or drug tolerance is commonly encountered in pharmacology, when a subject's reaction to a drug is reduced at a later time even though the dose or concentration at the effect site is the same. This means that larger doses are required to achieve the same effect...
. In some instances, such as with the soybean cultivars 'Dowling', 'Jackson', and 'Palmetto', resistance to the soybean aphid results from a combination of both antibiosis and antixenosis. In the 'Dowling' cultivar, resistance is conferred by a single dominant gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
(Rag1). Soybean plants that are resistant to the soybean aphid can cause both reduced fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
and longevity
Longevity
The word "longevity" is sometimes used as a synonym for "life expectancy" in demography or known as "long life", especially when it concerns someone or something lasting longer than expected ....
in soybean aphids. In the case of antibiosis, certain life stages of the soybean aphid may be more susceptible than others. For example, nymphs have higher rates of metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
than other life stages, ingest more phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
, and are thus exposed to larger quantities of antibiotic compounds. Expression of antibiotic factors in resistant soybean plants that negatively affect soybean aphids has been shown to remain constant throughout the growing season, remaining unaffected by the physiological maturity of the plant. Colonization of resistant soybean cultivars can vary between years depending upon the level of infestation, with resistant plants showing lower levels of resistance in years with significant levels of soybean aphid infestation. Physical characteristics of soybean, such as dense pubescence, have thus far proven incapable of reducing colonization by soybean aphids.
Natural enemies
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, the soybean aphid experiences pressure from over 30 species of predators, 8 species of parasitoids, and some fungal pathogens. In Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, where the soybean aphid is considered an occasional pest, evidence indicates the use of insecticides to control soybean aphids may not always be necessary due to suppression of the insect to subeconomic densities by natural enemies alone. In North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, the dominant natural enemies in soybean
Soybean
The soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
are generalist predators. Exclusion cage experiments have provided evidence that predators can play an important role in suppression of the soybean aphid. Impacts from predators include both the ability to suppress colony establishment early in the season as well as respond to increased densities of soybean aphids late in the season.
One of the most important predators of soybean aphids in North America is the insidious flower bug (Orius insidiosus (Say)). The insidious flower bug has its greatest impact on early to mid-season populations of soybean aphids and is often able to keep soybean aphid densities low. Fox et al. (2004) hypothesized that the impact from this predator early in the season could be attributed to small plant size and sparse canopies, which aid the insidious flower bug by reducing foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
time and decreasing the number of places soybean aphids can hide (i.e., enemy-free space). In addition, synomones released by soybean after being colonized by soybean aphids may aid the insidious flower bug in host location. When populations of soybean aphids reach very high densities, top-down pressure exerted by the insidious flower bug may fail to suppress colony growth of soybean aphids.
Another group of predators that plays a key role in suppression of populations of soybean aphids in North America is lady beetles (Coccinellidae spp.). Some prevalent species in soybean include the twospotted lady beetle (Adalia bipunctata L.), the sevenspotted lady beetle
Coccinella septempunctata
Coccinella septempunctata, the seven-spot ladybird , is the most common ladybird in Europe...
(Coccinella septempunctata L.), the spotted lady beetle
Spotted lady beetle
Coleomegilla maculata, commonly known as the spotted lady beetle, pink spotted lady beetle or twelve-spotted lady beetle, is a large coccinellid beetle native to North America...
(Coleomegilla maculata De Geer), the polished lady beetle (Cycloneda munda (Say)), the multicolored Asian lady beetle (Harmonia axyridis (Pallas)), the convergent lady beetle
Convergent lady beetle
Hippodamia convergens, commonly known as the convergent lady beetle, is one of the most common lady beetles in North America and is found throughout the continent. Aphids form their main diet and they are used for the biological control of these pests.-Life cycle:The female lady beetle lays 200 to...
(Hippodamia convergens Guérin-Méneville), and the thirteen spotted lady beetle (Hippodamia tredecimpunctata L.).
Generalist
Generalist may refer to:* a person with a wide array of knowledge, the opposite of which is a specialist.* a physician who is focused on primary care and is not a specialist in a certain medical field...
predators, lady beetles are able to feed on alternate prey when soybean aphids are at low densities. Other characteristics of lady beetles that are advantageous in times of soybean aphid scarcity include developmental delays of certain life stages, decreased body weights, and reduced clutch
Clutch
A clutch is a mechanical device which provides for the transmission of power from one component to another...
sizes. One of the most competitive lady beetles in North America, the multicolored Asian lady beetle, is of exotic origin. When soybean aphids are plentiful, an adult multicolored Asian lady beetle has the capacity to consume 160 soybean aphids per day.
Other foliar-foraging predators that are present North American soybean fields that may play a role in suppression of soybean aphid populations include green lacewings (Chrysoperla spp.), brown lacewings (Hemerobius spp.), damsel bugs (Nabis spp.), big eyed bugs (Geocoris spp.), spined soldier bug
Spined soldier bug
Podisus maculiventris, the spined soldier bug is a species of insect common in North America. They are predators of gypsy moth caterpillars and the larvae of beetles such as the Colorado potato beetle and the Mexican bean beetle...
s (Podisus maculiventris (Say)), hover flies (Syrphidae spp.), and the aphid midge (Aphidoletes aphidimyza (Rondani)). Another group of predators that are present in soybean fields is ground beetle
Ground beetle
Ground beetles are a large, cosmopolitan family of beetles, Carabidae, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe.-Description and ecology:...
s (Carabidae spp.); however, field experiments have shown limited to no impact from these predators on populations of soybean aphids due to the fact that ground beetles rarely scale soybean plants for prey. While parasitoids of the soybean aphid have a large impact on colonies in Asia—Lysiphlebia japonica (Ashmead) can have a soybean aphid parasitism rate as high as 52.6% in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
—parasitoids are thought to exert only minimal pressure on soybean aphids in North America.
Management
The use of insecticides to control populations of soybean aphids in soybean is the most effective management tactic in North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. Insecticides available to soybean producers for controlling soybean aphids include both foliar-applied treatments and seed-applied treatments. Although seed-applied treatments have proven to be a convenient delivery method for insect control, studies have experienced inconsistent results regarding their efficacy
Efficacy
Efficacy is the capacity to produce an effect. It has different specific meanings in different fields. In medicine, it is the ability of an intervention or drug to reproduce a desired effect in expert hands and under ideal circumstances.- Healthcare :...
against the soybean aphid. Management decisions should be made with an understanding of soybean aphid life history and sound scouting practices rooted in the principles of integrated pest management
Integrated Pest Management
Integrated pest management is an ecological approach to agricultural pest control that integrates pesticides/herbicides into a management system incorporating a range of practices for economic control of a pest...
.
The current economic threshold
Economic threshold
In integrated pest management, the economic threshold is the density of a pest at which a control treatment will provide an economic return....
for soybean aphids states that an insecticide application is warranted when soybean aphid densities reach 250 soybean aphids per plant, 80% of sampled plants are infested, the population is currently increasing, and few natural enemies are observed in the field. This recommendation is only valid from the R1 (beginning bloom) to R5 (beginning seed) growth stages and is based on an economic injury level of 674 soybean aphids per plant. Due to the clumped spatial distribution of soybean aphids, Onstad et al. (2005) recommend that 50 plants should be sampled within a field to attain an accurate representation of densities of soybean aphids. Soybean producers can choose from a variety of foliar insecticides from the carbamate
Carbamate
Carbamates are organic compounds derived from carbamic acid . A carbamate group, carbamate ester, and carbamic acids are functional groups that are inter-related structurally and often are interconverted chemically. Carbamate esters are also called urethanes.-Synthesis:Carbamic acids are derived...
, pyrethroid
Pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...
, and organophosphate
Organophosphate
An organophosphate is the general name for esters of phosphoric acid. Phosphates are probably the most pervasive organophosphorus compounds. Many of the most important biochemicals are organophosphates, including DNA and RNA as well as many cofactors that are essential for life...
chemical families to control soybean aphids.
Evidence indicates that foliar insecticide applications can reduce symptoms associated with soybean aphid infestations, including curled leaves, shortened stems, stunted plants, and premature defoliation. Foliar insecticide applications can also prevent yield loss associated with high densities of soybean aphids. However, some risks are associated with the use of foliar insecticide applications, especially if integrated pest management principles are abandoned. A single, well-timed application may not sufficiently control soybean aphids and prevent yield loss, especially if large quantities of soybean aphids are surviving on lower leaves. Foliar insecticide applications can work detrimentally if nontarget effects are experienced, such as the unintended death of beneficial natural enemies.
External links
- Soybean Aphid at University of Illinois at Urbana-Champaign
- Soybean Aphid at Iowa State University