In entomology

Entomology

Entomology is the scientific study of insects, a branch of arthropodology...

, the term petiole is most commonly used to refer to the constricted first (and sometimes second) metasoma

Metasoma

The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circulatory system, and the apical segments are typically...

l segment of members of the Hymenoptera

Hymenoptera

Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...

n suborder Apocrita

Apocrita

Apocrita is a suborder of insects in the order Hymenoptera.Apocrita includes wasps, bees and ants, and consists of many families. It includes the most advanced hymenopterans and is distinguished from Symphyta by the narrow "waist" formed between the first two segments of the actual abdomen; the...

; it may be used to refer to other insects with similar body shapes, where the metasomal base is constricted. It is occasionally called a pedicel, but, in entomology, that term is more correctly reserved for the second segment of the antenna

Antenna (biology)

Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....

.

The portion of the metasoma posterior to the petiole (and postpetiole in Myrmicinae

Myrmicinae

Myrmicinae is a subfamily of ants. There are about 140 genera within the group, with the family being cosmopolitan. The pupae lack cocoons. Some species retain a functional sting. The petioles of Myrmicinae consist of two nodes...

) is known as the gaster

Gaster

The gaster is the bulbous posterior portion of the metasoma found in Apocrita Hymenoptera . This begins with abdominal segment III on most ants, but some make a postpetiole out of segment III, in which case the gaster begins with abdominal segment IV....

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Other uses

• The term may also be used in the context of wing veins
  Insect wing
  Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
  
  , where a wing cell that is ordinarily four-sided is reduced to a triangle with a stalk (the cell thus being petiolate).
• It is also used to refer to the stalk at the base of paper wasp
  Paper wasp
  Paper wasps are -long wasps that gather fibers from dead wood and plant stems, which they mix with saliva, and use to construct water-resistant nests made of gray or brown papery material...
  
  nests.