''Evania appendigaster'', also known as the blue-eyed ensign wasp, is a species of

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...

in the family

Evaniidae Evaniidae is a family of parasitoid wasps also known as ensign wasps, nightshade wasps, hatchet wasps, or cockroach egg parasitoid wasps. They number around 20 extant genera containing over 400 described species, and are found all over the world ...

. Its native range is not known, but it likely originated in

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

. Today it occurs throughout the

tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referr ...

and subtropics and in many

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

regions. As with the rest of its family, the blue-eyed ensign wasp is a parasitoid known for specializing on

cockroach Cockroaches (or roaches) are a Paraphyly, paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are we ...

eggs.Strange, L. A
A Cockroach Egg Parasitoid, ''Evania appendigaster'' (Linnaeus) (Hymenoptera: Evaniidae).
EENY-162 (IN319). Entomology and Nematology. Florida Cooperative Extension Service. University of Florida IFAS. 2000.

Description

This is one of the larger ensign wasps, with forewings up to about 7 millimeters long. It is distinguished from other species by the wide separation of the first and second sections of the coxa, the segment of the

leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element ca ...

that attaches to the body. Its body is black in color with contrasting blue eyes. The abdominal petiole, the constricted stalk that holds the posterior section of the abdomen, or gaster, is attached high on the body. The gaster is laterally compressed and oval to nearly triangular in shape, held in a flaglike fashion and resembling an

ensign An ensign is the national flag flown on a vessel to indicate nationality. The ensign is the largest flag, generally flown at the stern (rear) of the ship while in port. The naval ensign (also known as war ensign), used on warships, may be diffe ...

, a characteristic of the family that inspired the common name ensign wasp.

Biology

This wasp reproduces by laying eggs into egg cases, or

ootheca An ootheca (pl. ''oothecae'' ) is a type of egg mass made by any member of a variety of species including mollusks (such as ''Turbinella laevigata''), mantises, and cockroaches. The word is a Latinized combination of ''oo-'', meaning "egg", f ...

e, of cockroaches. The wasp

larva A larva (; plural larvae ) 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 use the cockroach eggs as a food source. Host cockroaches include the American cockroach (''Periplaneta americana''),

Australian cockroach The Australian cockroach (''Periplaneta australasiae'') is a common species of tropical cockroach, with a length of . It is brown overall, with the tegmina having a conspicuous lateral pale stripe or margin, and the pronotum (head shield) with a ...

(''P. australasiae''),

brown cockroach The brown cockroach (''Periplaneta brunnea'') is a species of cockroach in the family Blattidae. It is probably originally native to Africa, but today it has a circumtropical distribution, having been widely introduced.

(''P. brunnea''), Oriental cockroach (''Blatta orientalis''), whitemargined cockroach (''Melanozosteria soror''), and harlequin cockroach (''Neostylopyga rhombifolia''). The complete life cycle of the species is summarized on a video available online. Detailed descriptions of the oviposition process in this species have been published. As one 1920 account describes it, "the Evaniid left the inside wall of the confining tumbler, ran over the Blattid ootheca, crawled over the surface momentarily as she actively vibrated her antenna and finally settled upon it with the long axis of her body parallel with the long axis of the egg mass as it lay upon its right side. Having satisfactorily settled herself, lying upon her right side she extended her ovipositor and crawling slightly forward she punctured the ootheca in the fifth egg cell of the left side, remaining in position for about fifteen minutes. She then left the egg mass and resting upon the inside wall of the tumbler actively cleaned the ovipositor, wings and antennae." As a 1957 account describes the "peculiar" egg-laying behavior, "the female lies on her side and, with legs braced against the oötheca, penetrates the tough integument of the egg-capsule after about half-an-hour's hard labour." The process apparently requires "a good deal of hard work and much wriggling of the abdomen." Other authors describe it as a seven-step process. The wasp lands on the ootheca and drums on it with her antennae. During step two, she extends her ovipositor and taps on the ootheca in several places for up to ten minutes, apparently searching for an appropriate site. After a rest period she begins "drilling", repeatedly inserting her ovipositor. Step five is the actual oviposition stage, in which wasps "just sit on ootheca and lay eggs". Steps six and seven are the withdrawal of the ovipositor and departure, respectively. One egg is deposited in each cockroach egg capsule, and the wasp larva consumes all the eggs within it. The larva proceeds through five

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ...

s during development, stages which are distinguished by the changes in the unique

mandibles In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. The first instar has mandibles with small, sharp teeth which it must use to open the tough cockroach eggs. During the next two instars, the larva has longer mandibles which are "shaped like a gauntlet glove" with three teeth. The final two instars have thicker mandibles with a long, blunt upper tooth and a narrow, curving lower tooth. When the larva reaches about 8 millimeters in length it

pupa A pupa ( la, pupa, "doll"; plural: ''pupae'') is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in thei ...

tes. Upon maturity it cuts a hole in the egg capsule and exits. The adult wasp lives for two or three weeks. It may spend some time on plants such as parsley and

fennel Fennel (''Foeniculum vulgare'') is a flowering plant species in the carrot family. It is a hardy, perennial herb with yellow flowers and feathery leaves. It is indigenous to the shores of the Mediterranean but has become widely naturalized ...

. Competitors include '' Aprostocetus hagenowii'', another parasitoid wasp that attacks cockroach oothecae.

Research

The larvae of the species have been described in minute details. The complete mitochondrial

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

of this species has been

sequenced In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which suc ...

. The wasp may be a candidate for use as an agent of biological pest control of cockroaches. Control might be even better if the wasp were released along with ''A. hagenowii'', which tends to have a higher rate of parasitism. The wasp can be bred in laboratory conditions for later release. The parasitizing capacity depends on the density of host oothecae. The development and parasitisation rates are temperature-dependent.

References

{{Taxonbar, from=Q2171907 Evanioidea Hymenoptera of Africa Hymenoptera of Asia Hymenoptera of Australia Hymenoptera of Europe Hymenoptera of North America Hymenoptera of South America Wasps described in 1758 Taxa named by Carl Linnaeus