Low Host Specialization in the Cuckoo Wasp, Parnopes grandior, Weakens Chemical Mimicry but Does Not Lead to Local Adaption

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.

A sting affair: A global quantitative exploration of bee, wasp and ant hosts of velvet ants

“…The apparent lack of velvet ant species that are specialized to only one may have limited the evolution of precise mimicry [ 84 , 85 ], though a weaker but still significant chemical mimicry cannot be discarded if all the hosts come from e.g. the same genus [ 86 ].…”

Inter- and Intrasexual Variation in Cuticular Hydrocarbons in Trichrysis cyanea (Linnaeus, 1758) (Hymenoptera: Chrysididae)

“…Furthermore, the amount of hydrocarbons on the cuticle of cleptoparasitic H. rutilans is five times less compared to the host, a phenomenon termed chemical insignificance [20]. Female Chrysis mediata Linsenmeier, 1951 and Pseudochrysis neglecta (Shuckard, 1837) are able to mimic different chemotypes of their host species Odynerus spinipes (Linnaeus, 1758) [23,40], whereas the chrysidid Parnopes grandior (Pallas, 1771) evolved a weak mimicry to multiple host species of the genus Bembix, mimicking only one single intermediate CHC-profile that includes major characteristics of all its hosts [21]. Comparably, the different chemotypes found in T. cyanea females may indicate an adaptation to different hosts.…”

“…Females of some species sneak into the nesting holes of their hosts to lay their eggs without being detected by their hosts. To be able to do so, many cuckoo wasps appear to mimic the CHC profiles of their hosts, but the exact strategies might differ among species, ranging from chemical insignificance, i.e., a much-reduced amount of CHCs as compared to the host [20], to weak mimicry, i.e., CHC profiles intermediate to those of different host species, in species parasitizing a few closely related host species [21], and strong mimicry of single host species [22]. Other species do not need any form of mimicry as the females open already closed nesting holes of their hosts [23] or lay their eggs into their hosts' prey (e.g., [24]).…”

Effects of genotype and host environment on the cuticular hydrocarbon profiles of Lysiphlebus parasitoids and aggression by aphid-tending ants

“…While a few previous studies have explored chemical mimicry in parasitoids [64][65][66][67], questions relating to host specialization have primarily been addressed in social parasites that use CHCs to exploit their hosts. These include systems based on environmentally acquired compounds that do not lead to host specialization [6,68], as well as other cases in which chemical mimicry has been shown to drive specialization [12,13,69,70]. There is also evidence that specialization can be driven by selection for other forms of crypsis, as observed in stick insects which experience strong selection to match the colour patterns of different host plants [71].…”