Chemical camouflage: a key process in shaping an ant-treehopper and fig-fig wasp mutualistic network

Chemical Camouflage Induced by Diet in a Pest Treehopper on Host Plants

Ants patrol foliage and exert a strong selective pressure on herbivorous insects, being their primary predators. As ants are chemically oriented, some organisms that interact with them (myrmecophiles) use chemical strategies mediated by their cuticular hydrocarbons (CHCs) to deal with ants. Thus, a better understanding of the ecology and evolution of the mutualistic interactions between myrmecophiles and ants depends on the accurate recognition of these chemical strategies. Few studies have examined whether treehoppers may use an additional strategy called chemical camouflage to reduce ant aggression, and none considered highly polyphagous pest insects. We analyzed whether the chemical similarity of the CHC profiles of three host plants from three plant families (Fabaceae, Malvaceae, and Moraceae) and the facultative myrmecophilous honeydew-producing treehopper Aetalion reticulatum (Hemiptera: Aetalionidae), a pest of citrus plants, may play a role as a proximate mechanism serving as a protection against ant attacks on plants. We found a high similarity (>80%) between the CHCs of the treehoppers and two of their host plants. The treehoppers acquire CHCs through their diet, and the chemical similarity varies according to host plant. Chemical camouflage on host plants plays a role in the interaction of treehoppers with their ant mutualistic partners.

Two lines of defense in the pupas of ichneumonid wasp parasitoids associated with spider hosts

Insects in the pupal stage are vulnerable to various predators because the pupa is immobile. The pupas of parasitoid ichneumonid wasps (Ichneumonidae) associated with spider hosts have evolved two lines of defense against predators, namely a cocoon spun by the parasitoid larva and a web provided by the spider host. The web is derived from a normal or modified spider web built by the spider under manipulation by the penultimate instar of the parasitoid wasp. In laboratory experiments, we tested the efficacy of these two defensive lines using six potential predators with two different types of mouthparts coming from three foraging guilds. The presence of the cocoon significantly reduced predation. Scavengers with chewing mouthparts, e.g., cockroaches and crickets, attacked and consumed pupas within both sparse and strong cocoon walls. Scavengers with piercing mouthparts were able to attack pupas in cocoons with a sparse wall, but not with a strong wall. Collectors and true predators showed no interest in cocoons. The presence of a web increased pupa protection by up to 80% when the web was on the ground and by up to 95% when the web was in the air. Only scavengers with chewing mouthparts were able to reach and consume pupas sheltered by the web. We provide the first evidence of how the two lines of defense contribute to parasitoid defense during the pupal stage.

Antipredator strategies of pupae: how to avoid predation in an immobile life stage?

Antipredator strategies of the pupal stage in insects have received little attention in comparison to larval or adult stages. This is despite the fact that predation risk can be high during the pupal stage, making it a critical stage for subsequent fitness. The immobile pupae are not, however, defenceless; a wide range of antipredator strategies have evolved against invertebrate and vertebrate predators. The most common strategy seems to be 'avoiding encounters with predators' by actively hiding in vegetation and soil or via cryptic coloration and masquerade. Pupae have also evolved behavioural and secondary defences such as defensive toxins, physical defences or deimatic movements and sounds. Interestingly, warning coloration used to advertise unprofitability has evolved very rarely, even though the pupal stage often contains defensive toxins in chemically defended species. In some species, pupae gain protection from conspecifics or mimic chemical and auditory signals and thereby manipulate other species to protect them. Our literature survey highlights the importance of studying selection pressures across an individual's life stages to predict how ontogenetic variation in selective environments shapes individual fitness and population dynamics in insects. Finally, we also suggest interesting avenues for future research to pursue. This article is part of the theme issue 'The evolution of complete metamorphosis'.