File: <evaniid.htm>                                                 [For educational purposes only]        Glossary            <Principal Natural Enemy Groups >             <Citations>             <Home>


HYMENOPTERA, Evaniidae (Evanioidea).-- --  <Images> & <Juveniles>


Description & Statistics


          Evaniidae. -- The ensign wasps are black, and resemble spiders.  They average 10-16 mm long. The abdomen is small and oval and is attached by a petiole to the propodeum much above the base of the hind coxae ; it is carried almost like a flag (hence the common name for this family.) These wasps are parasitoids of the egg capsules of cockroaches and may be found in buildings or other places where cockroaches roam.


There were more than 404 species known in this family as of 2010, all of which are believed to be parasitic in the egg capsules of cockroaches (Clausen 1940/1962).  Early researchers mistakenly believed that some species were parasitic on other stages of cockroaches.  Biological studies on Zeuxevania splendidula Costa (Genieys 1924) developing in the egg capsules of Loboptera decepiens Germ. in Europe, revealed that the parasitoid egg was deposited within one of the eggs in the capsule before the covering was completely hardened.  This is in accord with the habit of many other parasitoids of eggs contained within a capsule or covered with an appreciable quantity of mucilaginous material that hardens rapidly, as for example in the scelionid parasitoids of grasshopper and mantid eggs (Clausen 1940/1962).  They are very numerous in the tropics. 


Mason (1993) reported that the body is short and stout, with a typical appearance.  Antennae are elbowed with 11 (rarely 8) flagellar segments in both sexes.  The legs are relatively long.  The hind wing has the jugal lobe separated from the claval lobe by a deep incision.  The metasoma is relatively small and compressed, attached high on the propodeum by a curved, tubular petiole.  The ovipositor is short and mostly hidden.


Kieffer (1912) revised and Hedicke (1939a) catalogued the world species.  Townes (1949) reviewed the genera and species of North America.  Crosskey (1951) revised the British species.  Oehlke (1984) revised the German species.  Pagliano (1986) revixed the Italian species.


The egg is cylindrical in form, 1.0 mm in length, 0.25 mm in greatest width, slightly curved, and with one end markedly constricted and terminating in a broadly conical structure which bears a minute pedicel.  First instar larvae are somewhat cylindrical in form with 13 distinct segments, simple but strongly extruded mandibles, and a complete internal tracheal system, but no spiracles.  In this stage feeding is confined to the contents of the single egg, but following the first molt the neighboring eggs in the capsule come under attack.  The first stage larva is therefore a true egg parasitoid, but it becomes an egg predator after the molt.  The second instar larva is globular in form but otherwise closely resembles the preceding instar, the distinguishing characters being those of the head.  The 3rd & last instar larvae are very robust, about twice as long as wide, with the head large and the mandibles still simple.  There are no integumentary spines, sensory setae, or sculpturing upon the body.  The tracheal system is now open, with nine pairs of spiracles located on the 1st and 3rd thoracic and the first seven abdominal segments.  Each of the seven abdominal segments possesses an accessory ventral commissure in addition to the usual anterior and posterior commissures.  Only a single individual is able to develop to maturity in each egg capsule.  Winter is passed in the mature larval stage within the capsule, and adult emergence takes place in late spring or early summer (Clausen 1940/1962).



References:   Please refer to  <biology.ref.htm>, [Additional references may be found at:  MELVYL Library]