Hunger wasps
| Hunger wasps | ||||||||||
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Evania appendigaster |
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Evaniidae | ||||||||||
| Latreille , 1802 |
The Evaniidae , German often because of the small metasoma that gives the animal a "starved" appearance, evaniidae called, are a family of Hymenoptera. In all species whose biology is known, the larvae live inside the oothecae of cockroach species and feed on their eggs. The 435 known species (as of: 2005) live worldwide, with a distribution focus in the tropics.
features
Hunger wasps are small to medium-sized animals with a stocky build, between two and about eighteen millimeters in length (but most species are quite large for parasitic wasps). The animals are almost unmistakable by their body shape. As with all species of the superfamily Evanioidea, the free abdomen (metasoma or gaster) sits very high on the propodeum, so when viewed from the side, not between the rear hips, but much more dorsally. The species of the family always have a strikingly small abdomen with a characteristic shape. Its first segment (i.e., anatomically the second abdominal segment) is drawn out into a long and thin stalk (petiolus). The remainder of the abdomen is, in contrast, abruptly enlarged from an oval to triangular shape ("ax-shaped"). It is strongly compressed laterally with scleral overlapping sclerites, mostly shiny and remarkably small in relation to body size. In life it is constantly moved up and down, which reminded English editors of a signal flag (hence English "ensign wasps"). The ovipositor of the female is always short, in most species it barely protrudes over the tip of the abdomen. The ovipositor sheath is significantly wider than the ovipositor.
The middle section of the body (mesosoma) of the hunger wasps is always heavily sclerotized with a clearly sculptured surface. The rear of the three pairs of legs is greatly enlarged, it extends far beyond the tip of the abdomen. The wing veins of the forewings are extremely variable between the genera with one to seven closed cells. It is always strongly reduced in the hind wing. In both pairs of wings, the membrane has a small, lobed appendix in the posterior corners, the jugal field (according to other authors: anal field). Such an attachment does not appear in other " Legims ", it is a common feature of the hunger wasps with the Aculeata . Few genera are short-winged (brachypter) or even completely wingless (apter). The very short and broad, round head when viewed from the front sits tightly and slightly offset on the pronotum, which is also strongly shortened. It is surmounted by the trunk, which gives the animals a hunched look. On the head sit thread-like antennae, sometimes somewhat culled towards the tip, in the female, which consist of thirteen segments in both sexes (exceptions for the genera Decevania and Hyptia from South America).
Typically, males and females of hunger wasps are of different sizes and are drawn differently. This sometimes makes it difficult to identify belonging to the same species. It is quite likely that some older descriptions described males and females as different species.
Way of life
In all species whose way of life has become known so far, the female lays her eggs in the oothecae of cockroach species. The larva feeds on the eggs. However, of the more than 400 described hunger wasp species, biology is only available for about fifteen species, these are mainly species from Europe and North America as well as those that live with commercially important cockroach species ( pests ). This special way of life creates problems in the classification: According to the definition, the hunger wasps are not “ parasitoids ” (since the larvae eats more than an egg), but should be considered “predators”. The problem mainly concerns the nomenclature, however, the actual way of life is very similar to that of the other hymenoptera known as parasitoids.
The Evaniid female first seeks out the ootheca. For cockroaches that carry the ootheca with them, they sit on it. This is noticed by the cockroach, which tries to get rid of the parasite with wiping movements of the hind legs, but mostly unsuccessfully. In species that bury their oothecae, the hunger wasp digs them free. It then carefully digs them in again after the eggs have been laid. It takes some time to pierce the often stiff and hard outer shell of the ootheca, about fifteen to thirty minutes with Evania appendigaster . In all known cases, the female wasp lays only one egg per ootheca. The hatching larva now eats the cockroach eggs. Five larval stages have been described, which can be distinguished by the shape of the mandibles. The fully grown larva pupates in the ootheca without a self-spun pupal shell. The hatched imago eats a hole in the outer shell with its mouthparts (so it does not use the opening seam like the cockroaches themselves). The adults are rarely mentioned as flower visitors. It is not known whether all species consume food and what significance their food intake may have. Hunger wasps can pass through numerous generations a year, especially in warmer latitudes; three to four have been proven. In Europe there is usually only one generation per year outdoors.
Economic importance
The parasitization rate of cockroach booths by hunger wasps can be quite significant. In investigations of the species Evania appendigaster on Periplaneta americana , about one third of the oothecae were parasitized. It was therefore considered to use hunger wasps for biological pest control of cockroach species. However, previous approaches tend to focus on other parasitoids such as Comperia merceti (family Encyrtidae ) and Tetrastichus hagenowii (family Eulophidae ).
distribution
The family is distributed worldwide, with most species (like their hosts) living in the tropics. A number of species are considered to have been introduced and naturalized around the world. Like their hosts (synanthropic cockroaches), they probably come from South or East Asia.
So far, three species have been identified in Germany.
- Evania appendigaster , distributed worldwide on synanthropic cockroaches.
- Prosevania fuscipes , distributed worldwide on synanthropic cockroaches.
- Brachygaster minuta , on wood cockroaches ( Ectobius spp.). Ootheca parasitization rate (in England) around 10%.
Systematics
The assignment to the superfamily Evainiodea is beyond question, because it is the type family. The relationships between the Evanioidea have not been conclusively clarified. The most likely sister group is the superfamily Ceraphronoidea .
No subfamilies are recognized within the family. The living species are divided into twenty genera.
Fossil record
There are relatively few fossils of hunger wasps. The earliest fossils that can be safely assigned to the family come from the Lower Cretaceous . There are compression fossils made of limestone as well as inclusions in amber. Even earlier finds from the Jura are now mostly assigned to representatives from the trunk group of the Evanioidea from extinct families. The relationship between the Cretaceous species and the modern families Aulacidae and Gasteruptiidae is also not fully understood. The representatives of that time agree well with the recent hunger wasps in their shape and body structure (viewed from a few plesiomorphic features).
swell
- Andrew Robert Deans: Evaniidae. Ensign Wasps. Tree of life web project.
- Andrew Robert Deans (2004): Exploring the evolution and taxonomy of Evaniidae (Hymenoptera), a charismatic and enigmatic family of insects. Diss., University of Illinois.
- AR Deans & M. Huben (2003): Annotated key to the ensign wasp (Hymenoptera: Evaniidae) genera of the world, with descriptions of three new genera. Proceedings of the Entomological Society of Washington 105: 859-875.
- ^ Lionel A. Stange A Cockroach Egg Parasitoid, Evania appendigaster (Linnaeus) (Hymenoptera: Evaniidae). University of Florida Institute of Food and Agricultural Sciences (IFAS) document EENY-162. on-line
- ↑ Celia Mateus & António Mexia (2004): The use of IPM for cockroach (Dictyoptera: Blattaria) control. Integrated Protection of Stored Products. IOBC Bulletin Vol. 27 (9): 27-39.
- ↑ Joachim Oehlke (1984): Contributions to the insect fauna of the GDR: Hymenoptera - Evanioidea, Stephanoidea, Trigonanlyoidea. Faunistic treatises (Staatliches Museum für Tierkunde Dresden) 11 (13): 161-190.
- ↑ Ingmar Wall (1994): Rare Hymenoptera from Central, Western and Southern Europe (Hymenoptera Apocrita: Stephanoidea, Evanioidea, Trigonalyoidea). Entomofauna Volume 15, Issue 14: 137-184.
- ↑ Alexandr P. Rasnitsyn & Denis J. Brothers (2007): Two new hymenopteran fossils from the mid-Cretaceous of southern Africa (Hymenoptera: Jurapriidae, Evaniidae). African Invertebrates Vol. 48 (1): 193-202.
- ↑ Michael S. Engel (2006): Two ensign wasps in Cretaceous amber from New Jersey and Myanmar (Hymenoptera: Evaniidae). Polskie pismo entomologicze 75: 443-454.