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

AbstractAssassin or robber flies belong to the family Asilidae, one of the most diverse fly families, with over 7400 described species worldwide. Adults are predators on mostly smaller insects which they catch on the wing; larvae are predators on soft bodied arthropods in the soil or rotting wood, usually beetle (Coleoptera) larvae, often curl or white grubs (Scarabaeidae). Predation by larval and adult Asilidae puts downward pressure on populations of their prey above and below ground. Because asilid larvae are cryptic, the immature stages of few species have been described, thus hampering our ability to identify larvae. We describe and illustrate the late instar larva and pupa of one 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 the fine detail of the larval head capsule and mouthparts using scanning electron microscopy (SEM) for the first time in Asilidae. The larva and pupa of B. splendidissimus are similar to other Asilidae but larger and more robust. The larva has a broad maxillae and long narrow mandibular hooks with an acute tip armed with a row of recurved spines. Our SEM studies detail the grooves on the inner surface of the mandible that form a feeding channel when the mandibles are appressed. Thus, the mandibular hooks are the insect equivalent of a Swiss army knife, with at least four functions: to pierce the prey, hold the prey, inject venom and extract nutrients from the prey. Asilid pupae have a well‐developed armature on the head, thorax and abdominal tergites, for drilling up out of the soil on adult eclosion. The pupa has distinct anterior and posterior antennal spinous processes and anterior and posterior mesothoracic spinous processes, and the tip of the abdomen has large, dorsally curved dorsal posterolateral processes and very small ventral posterolateral spinous processes. All the dorsal armature on the pupal abdominal segments are articulated spurs, rather than a mixture of fixed spines and spurs, as found in many asilid pupae.