This is a rare family of Diptera, several species of which are known to parasitize larvae of Coleoptera and a few are internally parasitic on locusts.
Biology & Behavior
Handlirsch (1882, 1883) and Brauer (1883, 1884) gave early accounts of the host preferences of the family on Hirmoneura obscura Meig., parasitic on Amphimallus solstitialis L. (= Rhizotrogus sp.) pupae. Riley (1883a, 1884) elaborated on their observations. Hirmoneura obscura adults are present in the field during July and early August, when females are frequently observed laying eggs in abandoned burrows of Anthaxia quadripunctata L., and probably of other coleopterous borers, in broken branches, spruce poles, etc., from which bark had been removed. The parasitoid seems closely associated with spruce, and adults could be found abundant only at the borders of spruce forests where fallen trees or branches were common, or in fields bordered by fences made of spruce. No oviposition was observed in hosts in living trees. During oviposition the female parasitoid inserts her abdomen tip deeply into the exit hole of the beetle and lays a mass of eggs.
After hatching, young larvae make their way to the surface of the branch or pole, assume an erect position and are thought to then be blown away by wind. Riley (1883a, 1884) hinted that they might be carried into the soil by adult host beetles, but Clausen (1940) thought this improbable, for the normal movements of the beetles would not bring them into contact with the young larvae and in any case just carrying them into the soil would not be advantageous to establishing contact with a pupa or grub that was in a vulnerable stage for attack. Brauer (1883, 1884) found parasitization of Amphimallus pupae to be highest within 3 m. of the spruce fence and that it decreased rapidly with an increase in distance away.
Second instar larvae are found in living host pupae during June and 3rd instar soon thereafter. The host beetle is fully formed and its integument heavily chitinized before it dies. The parasitoid is oriented in the same way as the host. After the fluid contents are completely consumed, it makes a large hole in the venter of the thoracic region and eventually pupates alongside the host remains or partly extruded from the opening (Clausen 1940/1962). It is thought that the mature larva persists until the following season, because some individuals that had emerged from host pupae during June did not pupate by August. In the field, the pupae work their way to the soil surface just before they emerge as adult flies. The pupal shells were observed in large numbers in the field, each standing upright with its posterior end held in the burrow by the caudal fork and spines.
Brauer (1883, 1884) concluded that the life cycle of Hirmoneura must cover two years just as its host. Beetles lay their eggs in late summer, with larval and pupal stages being completed by autumn of the following year. Newly formed adults hibernate in their pupal cells and then appear in the field in June of the 2nd year. Hirmoneura eggs hatch in July and early August. At this time no beetle pupae are available, and thus they wait until the following May or June to develop. If the protracted larval diapause is normal, the 2-year cycle is obligatory; for larval development is not completed until the season following oviposition, and the second winter is then passed in the mature larval or pupal stage (Clausen 1940/1962).
Brauer tried to determine how and when 1st instar larvae reach their hosts. He noted that the in the case of Anthrax sp. the 1st instar larva enters the Agrotis larva and then awaits its pupation before completing its own development. Also, Mantispa hibernates in the first stage and then searches for the spider egg masses the following spring. First instar larvae of Hirmoneura were found to be very long-lived, and Handlirsch (1882, 1883) found one that remained alive without food from August 17th to October 29th. This suggests the possibility of living overwinter in the free condition, yet Clausen (1940) thought it more probable that they enter the more mature beetle larvae during autumn, remaining inactive until after host pupation in late springtime.
In South America, Hirmoneura exotica Wied. lays its eggs in the tunnels of wood boring bees (Brauer 1883, 1884). Spencer (1931, 1932) observed the manner of oviposition of Parasymmictus clausus O.S. (= Rhynchocephalus sackeni Will.). Females inserted their ovipositors in holes and cracks of telegraph poles in which no borers of any kind were present. They remained in that position for an hour or more. Circumstantial evidence suggests that larvae of cerambycid borers of genera Asemum and Xylotrechus are probable hosts. Stuardo (1935) found females of H. articulata Ph. to oviposit principally during late morning and early afternoon. They were attracted only to poles or posts lacking bark, and the ovipositor was inserted deeply into the crevices. While for one or more hours in that position, a female may lay a mass of eggs exceeding 100.
The behavior of lateral larval stages of two species that are solitary internal parasitoids of locusts in South Africa (Potgieter 1929), suggest that mature larvae of Symmictus costatus Loew are on the ground surface in association with Locusta vardalina Wlk. nighttime resting areas. An examination of living parasitized locusts showed that the partly grown parasitoid larva fed only on body fluids, with little injury to the host. This was judged by the normal oviposition and development of the female locust eggs. The Symmictus larva leaves the dead host when mature, and burrows into the soil to 2.5-50.0 cm. Pupation takes place soon thereafter if conditions are favorable, and the fly emerges ca. 14 days later. However, mature larvae are able to adapt themselves to adverse conditions by entering diapause (Potgieter 1929). Diapause may persist for 3.5 years, but normally the cycle is requires ca. one year (Potgieter 1929).
Trichopsidea ostracea Westw. in Australia is parasitic in adults of the plague grasshopper, Chortoicetes terminifera Wlk. Noble (1936) and Fuller (1938) published notes on the immature stages. Larvae are solitary, being found in the abdomen. This parasitoid leaves the host while it is still alive, which differs from Symmictus. The prepupal stage in soil extends over several months, and the pupal stage lasts 3 weeks. Field parasitization was ca. 5%.
For detailed descriptions of immature stages of Nemestrinidae please see (Clausen 1940/1962).