Cuticular Hydrocarbon Trails Released by Host Larvae Lose their Kairomonal Activity for Parasitoids by Solidification

Abstract

Successful host search by parasitic wasps is often mediated by host-associated chemical cues. The ectoparasitoid Holepyris sylvanidis is known to follow chemical trails released by host larvae of the confused flour beetle, Tribolium confusum, for short-range host location. Although the hexane-extractable trails consist of stable, long-chain cuticular hydrocarbons (CHCs) with low volatility, the kairomonal activity of a trail is lost two days after release. Here, we studied whether this loss of kairomonal activity is due to changes in the chemical trail composition induced by microbial activity. We chemically analyzed trails consisting of hexane extracts of T. confusum larvae after different time intervals past deposition under sterile and non-sterile conditions. GC-MS analyses revealed that the qualitative and quantitative pattern of the long-chain CHCs of larval trails did not significantly change over time, neither under non-sterile nor sterile conditions. Hence, our results show that the loss of kairomonal activity of host trails is not due to microbially induced changes of the CHC pattern of a trail. Interestingly, the kairomonal activity of trails consisting of host larval CHC extracts was recoverable after two days by applying hexane to them. After hexane evaporation, the parasitoids followed the reactivated host trails as they followed freshly laid ones. Cryo-scanning electron microscopy showed that the trails gradually formed filament-shaped microstructures within two days. This self-assemblage of CHCs was reversible by hexane application. Our study suggests that the long-chain CHCs of a host trail slowly undergo solidification by a self-assembling process, which reduces the accessibility of CHCs to the parasitoid’s receptors as such that the trail is no longer eliciting trail-following behavior.

Preference of black soldier fly larvae for feed substrate previously colonised by conspecific larvae

“…Candidate chemicals are cuticular hydrocarbons (CHCs) since these have a high molecular weight and may only be detectable by the larvae from a short distance or upon contact (Ferveur & Cobb, 2010). These chemicals may be left behind in the substrate, surfaces or feeding substrates via CHC trails (Awater‐Salendo et al, 2021; Ferveur & Cobb, 2010).…”

Keep Your Eggs Away: Ant Presence Reduces Ceratitis capitata Oviposition Behaviour through Trait-Mediated Indirect Interactions

“…Among the substances involved in chemical communication in ants, and candidates for being the kairomones triggering the observed effects, cuticular hydrocarbons (CHCs) might play a special role. CHCs are pheromones commonly used by ants and other insects to recognize nestmates and/or mutualists, but they may also be released in the environment and be involved, for example, in marking the home range [ 57 , 58 ], and they can be also used as kairomones [ 59 ]. Unfortunately, despite the fact that the CHCs of the two studied species have been analysed in previous studies (e.g., [ 22 , 35 ] for C. scutellaris , [ 60 ] for the T. nigerrimum complex), a comparative analysis to identify the effective molecules on available data is difficult because of the different laboratory standards used.…”

Detection of invasive and native beetle species within trees by chemical analysis of frass

“…CHCs of many adult insects are reported to be species specific 30 . In contrast, only a few reports of larval CHCs were found: one on blowfly larvae 31 , one on Tribolium confusum (Coleoptera, Tenebrionidae) 32 , and some on parasitic lepidopteran larvae which penetrate ant nests 33 . These reports describe age-dependent changes in larval CHCs (blowfly), kairomonal activity ( T .…”