Potential role of evasive flights and nest closures in an African sand wasp, Bembix sp near capensis Lepeletier 1845 (Hymenoptera Crabronidae), against a parasitic satellite fly

The brood of ground-nesting Hymenoptera is often the victim of parasitic flies. We observed the behavioural relationships between the sand wasp Bembix sp. near capensis Lepeletier 1845 (Hymenoptera Crabronidae) and its brood parasite Craticulina fimbriata Bezzi 1911 (Diptera Sarcophagidae) in Ouagadougou (Burkina Faso). Craticulina fimbriata females performed satellite flights in order to reach the nests of B. sp. near capensis, their frequency being higher when host provisioning activity was higher. The wasp made evasive manoeuvres when followed by the fly while coming back to the nest both with and without prey. Evasive flights effectively reduced the number of visits of the satellite fly into the nest. Wasps which closed their nest before every departure rather than leaving the nest entrance open seemed to suffer a lower frequency of satellite fly visits into the nest. Thus, both evasive manoeuvres and nest closure play a role in reducing the contact between C. fimbriata and the wasp provisions. We also recorded a rare phenomenon in digger wasps. About 30% of provisioning trips were followed by the immediate exit of the prey from the nest, showing that many of them were not paralysed. Prey escaped throughout the daily provisioning period, but less from nests that were usually closed by the wasps. Moreover, a relationship emerged between the frequency of escaping prey and satellite fly activity. Possible explanations of this phenomenon are discussed.