Abstract
Insect brood parasites have evolved a variety of strategies to avoid being detected by their hosts. Few previous studies on cuckoo wasps (Hymenoptera: Chrysididae), which are natural enemies of solitary wasps and bees, have shown that chemical mimicry, i.e., the biosynthesis of cuticular hydrocarbons (CHC) that match the host profile, evolved in several species. However, mimicry was not detected in all investigated host-parasite pairs. The effect of host range as a second factor that may play a role in evolution of mimicry has been neglected, since all previous studies were carried out on host specialists and at nesting sites where only one host species occurred. Here we studied the cuckoo wasp Parnopes grandior, which attacks many digger wasp species of the genus Bembix (Hymenoptera: Crabronidae). Given its weak host specialization, P. grandior may either locally adapt by increasing mimicry precision to only one of the sympatric hosts or it may evolve chemical insignificance by reducing the CHC profile complexity and/or CHCs amounts. At a study site harbouring three host species, we found evidence for a weak but appreciable chemical deception strategy in P. grandior. Indeed, the CHC profile of P. grandior was more similar to all sympatric Bembix species than to a non-host wasp species belonging to the same tribe as Bembix. Furthermore, P. grandior CHC profile was equally distant to all the hosts’ CHC profiles, thus not pointing towards local adaptation of the CHC profile to one of the hosts’ profile. We conducted behavioural assays suggesting that such weak mimicry is sufficient to reduce host aggression, even in absence of an insignificance strategy, which was not detected. Hence, we finally concluded that host range may indeed play a role in shaping the level of chemical mimicry in cuckoo wasps.
Highlights
Females of many insect brood parasites sneak into the host nests in order to deposit their eggs or larvae, a behaviour allowing parasites to leave chemical traces in the nests
They can be grouped into three main categories: (a) chemical mimicry, which occurs when a parasite synthetises de novo an odour bouquet matching that of the host’s bouquet [11], (b) chemical camouflage, which occurs when the host odour bouquet is acquired from the host [9] and (c) chemical insignificance, which occurs when the brood parasites have reduced recognition cues, which limit their chance of being perceived by the hosts [12]
It is likely that the dependence of insect brood parasites on their hosts imposes selection on the latter to avoid being recognised by the hosts, and such selection often involves the modification of host recognition cues, such as cuticular hydrocarbon (CHC) [6,11,49,50]
Summary
Females of many insect brood parasites sneak into the host nests in order to deposit their eggs or larvae, a behaviour allowing parasites to leave chemical traces in the nests. Chemical strategies to successfully avoid host aggression during nest invasion are common in parasitic aculeate Hymenoptera They can be grouped into three main categories: (a) chemical mimicry, which occurs when a parasite synthetises de novo an odour bouquet matching that of the host’s bouquet [11], (b) chemical camouflage, which occurs when the host odour bouquet is acquired from the host [9] and (c) chemical insignificance, which occurs when the brood parasites have reduced recognition cues, which limit their chance of being perceived by the hosts [12]. While the primary function of CHCs is to reduce desiccation, abrasion or infection, they commonly act as semiochemicals in different contexts of communication, including intra-specific and inter-specific recognition [7,13]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
