Asilinae

Dennis, Steve, Barnes, Jeffrey K. & Knutson, Lloyd, 2013, Review and analysis of information on the biology and morphology of immature stages of robber flies (Diptera: Asilidae), Zootaxa 3673 (1), pp. 1-64 : 5-6

Subfamily Asilinae

Female robber flies in the subfamily Asilinae drop eggs onto the substrate or onto vegetation, or by inserting their ovipositor into the soil, dry cow or horse dung, or rabbit pellets ( Asilus crabroniformis Linnaeus ); or in vegetation (in particular between the sheath and stem or dry seed heads of grasses); or onto wire fences (i.e., Mallophora ruficauda (Wiedemann) ; Castelo & Corley 2004a, Castelo et al. 2006). The number of eggs laid varies from 1 to 729 with most from 1 to 20. The largest numbers of eggs are produced by Mallophora spp., Megaphorus guildianus (Williston) , and Porasilus barbiellini Curran , which deposit them in clusters and cover them with a soft chalky-white albumin.

It seems that the more eggs produced per oviposition event, the smaller the size of the eggs. Eggs in ovipositions with 1 to 20 eggs, ranged in length from 0.80 to 2.80 mm and in width from 0.30 to 0.82 mm. For more extensive ovipositions, with 32 to 390 eggs, the eggs ranged in length from 0.80 to 1.01 mm and in width from 0.22 to 0.38 mm.

Eggs are most often white to creamy white, but can be yellowish white, pearly (shiny) whitish to pinkish, yellowish brown, light brown, or light gray. Eggs are most frequently elongate or oblong, but some genera have more or less oval eggs.

Asilinae eggs that have been examined with a scanning electron microscope (SEM) have surface features including striations, elevated bodies (nipples, tubercles), crevices, spherical bodies and globules, and reticulate sculpturing with different shapes of polygons. Antipalus varipes (Meigen) is unique in the subfamily Asilinae with eggs that have fine sand grains on them (except on one longitudinal side of the egg) from the sand in which they are oviposited.

Aeropyles are present or absent on Asilinae eggs. They may be evenly spread over the surface, except in the area of the micropyle, or more concentrated. They may be located on cone-shaped structures or on flat areas of the chorion. A micropyle has been observed for some, but not all eggs. The immediate area around the micropyle is typically smooth.

The egg stage lasts from 2 to 8 days with an average of approximately 6 days. When the larva emerges from the egg, it continues to live in the soil, decaying vegetable matter, or possibly dry horse and cow dung, where it feeds upon larvae in the insect families Chrysomelidae , Curculionidae , Scarabaeidae , and possibly Asilidae . Scarabaeidae larvae have been the most frequently reported prey.

The larval stage of Asilinae can be quite long, lasting from 1 to 3 years. The pupal stage is much shorter, lasting from 14 to 70 days.

Information on larval morphology has generally been published on the first two instars and mature larvae. For a number of species there are descriptions of pupal cases, although there are not many detailed descriptions. The literature contains figures of both the larvae and pupal cases.