How to measure patch encounter rate: decision-making mechanisms in the parasitic wasp Asobara tabida

Parasitic wasps are faced with the decision of where and for how long to search for hosts. Their leaving decisions depend on the rate at which new host-containing patches are encountered: parasitoids increase foraging efficiency by leaving earlier when patch encounter rates become higher. The mechanisms by which these often tiny insects can assess patch encounter rates have not been thoroughly investigated so far. The aim of the present study, where females of the braconid wasp Asobara tabida encountered patches after varying time intervals, was to measure the shape of the travel-time response curve and to analyse how information on inter-patch distances is translated into foraging behaviour. I examined several proxies for travel-time duration, like those of physiological nature as egg content, cues of senescence, amount of energy spent, or muscle fatigue, as well as true cognitive mechanisms, like measurement of distance or interval timing. Constraints in the wasp's ability to detect patch borders accurately after travelling, e.g. habituation to the patch odour or receptor blocking, are also discussed. From the data presented, most of the above-mentioned mechanisms and constraints can be rejected to work for A. tabida. The effects of inter-patch travel time are strongest when they are short, and even though it cannot be excluded that time measures are processed using an internal clock, I suggest that a Bayesian-like mechanism of timing, the biological basis of which might involve the build-up of neurosecretory material, is the most likely candidate influencing leaving decisions in A. tabida.