Immature stages of Blepharotes (Diptera: Asilidae), one of the world's largest assassin flies: multi-function mandibles and soil-drilling pupal spines and spurs

Abstract

Assassin or robberflies belong to the family Asilidae, one of the most diversefly families, with over 7400described species worldwide. Adults are predators on mostly smaller insects which they catch on the wing; larvaeare predators on soft bodied arthropods in the soil or rotting wood, usually beetle (Coleoptera) larvae, often curl orwhite grubs (Scarabaeidae). Predation by larval and adult Asilidae puts downward pressure on populations of theirprey above and below ground. Because asilid larvae are cryptic, the immature stages of few species have been de-scribed, thus hampering our ability to identify larvae. We describe and illustrate the late instar larva and pupa ofone of Australia's largest and most impressive asilid species,Blepharotes splendidissimus(Wiedemann) (Asilinae:Apocleini). Taxonomically useful variation in asilid larvae so far described occurs in the head and its appendages.We have examined thefine detail of the larval head capsule and mouthparts using scanning electron microscopy(SEM) for thefirst time in Asilidae. The larva and pupa ofB. splendidissimusare similar to other Asilidae butlarger and more robust. The larva has a broad maxillae and long narrow mandibular hooks with an acute tip armedwith a row of recurved spines. Our SEM studies detail the grooves on the inner surface of the mandible that form afeeding channel when the mandibles are appressed. Thus, the mandibular hooks are the insect equivalent of aSwiss army knife, with at least four functions: to pierce the prey, hold the prey, inject venom and extract nutrientsfrom the prey. Asilid pupae have a well-developed armature on the head, thorax and abdominal tergites, for dril-ling up out of the soil on adult eclosion. The pupa has distinct anterior and posterior antennal spinous processes andanterior and posterior mesothoracic spinous processes, and the tip of the abdomen has large, dorsally curved dorsalposterolateral processes and very small ventral posterolateral spinous processes. All the dorsal armature on thepupal abdominal segments are articulated spurs, rather than a mixture offixed spines and spurs, as found in manyasilid pupae.