Lebia grandis
Encyclopedia
Lebia grandis is a ground beetle in the family Carabidae
found in North America. It is a specialist predator
on the eggs
and larva
e of Colorado potato beetle
s, and its larvae are obligate parasitoid
s of Colorado potato beetle pupa
e.
. These are wide but rather shorter than the abdomen which protrudes posteriorly.
them. Each female can lay up to 1300 eggs over the course of a few months.
The eggs hatch after about two weeks and the first instar
larvae search out Colorado potato beetle larvae that are about to pupate. They may follow an odour trail left behind by the burrowing larvae and they need to reach the pupation chamber before it is sealed. They sink their mandible
s into the integument
of their hosts and start feeding, killing the host in the process. After moulting they cease feeding and soon metamorphose
into the pupal stage. Adult ground beetles emerge about three weeks after the eggs were hatched.
Because it specifically targets Colorado potato beetles and is native to North America, Lebia grandis shows promise as a biological control species in the United States. However it does not usually occur in sufficient numbers to effect complete control. Populations may need to be augmented by releasing adult beetles but rearing these in bulk presents certain difficulties that have not yet been overcome. Other predators such as the spotted lady beetle
(Coleomegilla maculata) also prey on Colorado potato beetles but Lebia grandis is constrained by its chrysomelid larval host to habituate potato fields while other predators may disperse to other sources of food.
The original host plant of the Colorado potato beetle, L. decemlineata was the buffalo bur, Solanum rostratum
, in Mexico. No association has been found between Lebia grandis and L. decemlineata on this host plant. In the 1850s, L. decemlineata began to feed on the potato plant and spread rapidly eastwards on potato crops. Lebia grandis may have had a relationship prior to this with the false potato beetle, Leptinotarsa juncta which feeds on horsenettle, Solanum carolinense. Another closely related chrysomid beetle, Leptinotarsa haldemani
is recorded from Texas, Oklahoma, Arizona and Mexico, where it lives on wild species of Physalis
and Solanum douglasii
, but its range does not overlap with Lebia grandis except possibly in Texas.
In an attempt to find the original species associated with Lebia grandis, research was undertaken examining its prey preferences and the suitability of the three chrysomelid
species, L. decemlineata, L. juncta and L. haldemani as hosts for its larvae.
Adult Lebia grandis beetles were offered suitable sized larvae of these three chrysomelid species and the number of larvae of each species that were eaten was noted. A similar experiment was performed using the eggs of the three chrysomelid species. The Lebia grandis adults showed no significant difference in the number of larvae of each prey species they chose to eat, but they did differentiate between their eggs. L. juncta egg consumption averaged nearly twice as high as L. decemlineata egg consumption, with L. haldemani being in an intermediate position.
In another experiment, a first instar larva of Lebia grandis was placed in close proximity to a 4th instar chrysomelid larva that was about to pupate. The success rate of parasitism in each of the three prey species was noted. Successful development of Lebia grandis from first instar larva to adult occurred with each of the three species of Leptinotarsa. However the success rate recorded for L. juncta was about 43% as compared to 12% for the other two species.
These studies would seem to support the view that Lebia grandis was originally exclusively a parasitoid of L. juncta, but that the opportunity afforded by its encounter with L. decemlineata less than 150 years ago enabled it to exploit this new and abundant food source.
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:...
found in North America. It is a specialist predator
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
on the eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e of Colorado potato beetle
Colorado potato beetle
The Colorado potato beetle , also known as the Colorado beetle, the ten-striped spearman, the ten-lined potato beetle or the potato bug, is an important pest of potato crops. It is approximately 10 mm long, with a bright yellow/orange body and five bold brown stripes along the length of each...
s, and its larvae are obligate parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
s of Colorado potato beetle pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
e.
Description
Lebia grandis is the largest species in its genus found in North America. It is about one centimetre long with a rusty orange head, thorax and legs, a black abdomen and an iridescent blue or purple lustre to the dark coloured elytraElytron
An elytron is a modified, hardened forewing of certain insect orders, notably beetles and a few of the true bugs ; in most true bugs, the forewings are instead called hemelytra, as only the basal half is thickened while the apex is membranous...
. These are wide but rather shorter than the abdomen which protrudes posteriorly.
Life cycle
Adult Lebia grandis ground beetles overwinter in soil in or near potato fields. In the spring Colorado potato beetles emerge from hibernation. By the time Lebia grandis beetles emerge a few weeks later, there are eggs and young larvae of their prey for them to eat and suitable pupae will soon be available for their larvae to attack. An adult beetle can eat about twenty three eggs or three third instar larvae of the Colorado potato beetle each day. After mating, the females lay eggs singly in the soil near potato plants. A glandular secretion causes soil granules to stick to the eggs which serves to camouflageCamouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
them. Each female can lay up to 1300 eggs over the course of a few months.
The eggs hatch after about two weeks and the first 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...
larvae search out Colorado potato beetle larvae that are about to pupate. They may follow an odour trail left behind by the burrowing larvae and they need to reach the pupation chamber before it is sealed. They sink their mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s into the integument
Integumentary system
The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages...
of their hosts and start feeding, killing the host in the process. After moulting they cease feeding and soon metamorphose
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
into the pupal stage. Adult ground beetles emerge about three weeks after the eggs were hatched.
Use in biological control
The significance of Lebia grandis in keeping Colorado Potato Beetle under control was not originally fully appreciated because of the largely nocturnal habits of the adult beetles and the subterranean existence of the larvae. In fact it was about a hundred years after its first description as a species that the larvae were discovered to have a parasitoid habit.Because it specifically targets Colorado potato beetles and is native to North America, Lebia grandis shows promise as a biological control species in the United States. However it does not usually occur in sufficient numbers to effect complete control. Populations may need to be augmented by releasing adult beetles but rearing these in bulk presents certain difficulties that have not yet been overcome. Other predators such as 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) also prey on Colorado potato beetles but Lebia grandis is constrained by its chrysomelid larval host to habituate potato fields while other predators may disperse to other sources of food.
Research
The historical records for Lebia grandis show that it was present in areas where L. decemlineata was not found. This would seem to imply that at one time it parasitized a different species.The original host plant of the Colorado potato beetle, L. decemlineata was the buffalo bur, Solanum rostratum
Solanum rostratum
Solanum rostratum is a species of nightshade that is native to the United States and northern and central Mexico. Common names include buffalo bur, spiny nightshade, and Texas thistle....
, in Mexico. No association has been found between Lebia grandis and L. decemlineata on this host plant. In the 1850s, L. decemlineata began to feed on the potato plant and spread rapidly eastwards on potato crops. Lebia grandis may have had a relationship prior to this with the false potato beetle, Leptinotarsa juncta which feeds on horsenettle, Solanum carolinense. Another closely related chrysomid beetle, Leptinotarsa haldemani
Leptinotarsa haldemani
Leptinotarsa haldemani is a glossy green beetle in the family Chrysomelidae. It is commonly known as Haldeman's green potato beetle. It was named in honour of Samuel Stehman Haldeman, a nineteenth century American entomologist who collected insect specimens in Texas.-Description:This little beetle...
is recorded from Texas, Oklahoma, Arizona and Mexico, where it lives on wild species of Physalis
Physalis
Physalis is a genus of plants in the nightshade family , native to warm temperate and subtropical regions throughout the world. The genus is characterised by the small orange fruit similar in size, shape and structure to a small tomato, but partly or fully enclosed in a large papery husk derived...
and Solanum douglasii
Solanum douglasii
Solanum douglasii is a species of nightshade known by the common name greenspot nightshade. It is native to the northern half of Mexico and the southwestern south-central United States. Its habitat includes scrub and woodland. It is a perennial herb or subshrub approaching two meters in maximum...
, but its range does not overlap with Lebia grandis except possibly in Texas.
In an attempt to find the original species associated with Lebia grandis, research was undertaken examining its prey preferences and the suitability of the three chrysomelid
Leaf beetle
Beetles in the family Chrysomelidae are commonly known as leaf beetles. This is a family of over 35,000 species in more than 2,500 genera, one of the largest and most commonly encountered of all beetle families....
species, L. decemlineata, L. juncta and L. haldemani as hosts for its larvae.
Adult Lebia grandis beetles were offered suitable sized larvae of these three chrysomelid species and the number of larvae of each species that were eaten was noted. A similar experiment was performed using the eggs of the three chrysomelid species. The Lebia grandis adults showed no significant difference in the number of larvae of each prey species they chose to eat, but they did differentiate between their eggs. L. juncta egg consumption averaged nearly twice as high as L. decemlineata egg consumption, with L. haldemani being in an intermediate position.
In another experiment, a first instar larva of Lebia grandis was placed in close proximity to a 4th instar chrysomelid larva that was about to pupate. The success rate of parasitism in each of the three prey species was noted. Successful development of Lebia grandis from first instar larva to adult occurred with each of the three species of Leptinotarsa. However the success rate recorded for L. juncta was about 43% as compared to 12% for the other two species.
These studies would seem to support the view that Lebia grandis was originally exclusively a parasitoid of L. juncta, but that the opportunity afforded by its encounter with L. decemlineata less than 150 years ago enabled it to exploit this new and abundant food source.