Insect cuticular hydrocarbon composition influences their interaction with spider capture threads

Abstract

Insects represent the main prey of spiders, and spiders and insects co-diversified in evolutionary history. One of the main features characterizing spiders is their web as trap to capture prey. Phylogenetically, the cribellate thread is one of the earliest thread types that was specialized to capture prey. In contrast to capture threads, it lacks adhesive glue and consists of nanofibers, which do not only adhere to insects via van der Waals forces, but also interact with the insects’ cuticular hydrocarbon (CHC) layer, thus enhancing adhesion. The CHC layer consist of multiple hydrocarbon types and is highly diverse between species. In this study, we show that CHC adhesion to cribellate capture threads is affected by CHC composition of the insect. We studied the interaction in detail for four different insect species with different CHC profiles and observed a differential migration of CHCs into the thread. The migration depends on the molecular structure of the hydrocarbon types as well as their viscosity, influenced by altering the ambient temperature during interaction. As a consequence, adhesion forces to CHC layers differ depending on their chemical composition. Our results match predictions based on biophysical properties of hydrocarbons, and show that cribellate spiders can exert selection pressure on the CHC composition of their insect prey.

Predation potential of the earwig Euborellia annulipes on fruit fly larvae and trophic interactions with the parasitoid Diachasmimorpha longicaudata

“…The cuticle of C. capitata larvae contains n‐alkanes and 2‐monomethyl alkanes as major compounds (Sutton & Steck, 1994); however, their extraction requires a longer time in hexane than that used in our study (Belenioti et al, 2022). We standardized the time interval for hexane washing (30 s) based on preliminary assays, in which hexane washing did not cause larval mortality or affect prey acceptance by the earwigs, as significant removal of CHCs can affect prey recognition (Joel et al, 2022; Xue et al, 2018). Therefore, our method likely removed chemical cues from the epicuticle of parasitized prey, such as those associated with mechanical damage by parasitoids or cues left during host handling by the parasitoid.…”

Physico-chemical properties of functionally adhesive spider silk nanofibres

“…by being electrostatically attracted to flying prey) 31 (2) establish adhesion by van der Waals and hygroscopic forces 29,44 and (3) embed the nanofibres into the cuticular hydrocarbons of the prey for enhancing adhesion. 27,53 Our GC-MS analysis found elevated levels of charged amino acids that could be crucial for the attraction to prey as well as the establishment of van der Waals forces. Glutamine, on the other hand, has been described to interact with water and facilitate the supercontraction of major ampullate silk.…”

“…This amino acid might facilitate the hydrophobic interactions between cribellate silk and the hydrocarbons of the insect cuticle. 27,53…”

“…If capillary forces, perhaps in an interplay with van der Waals forces, are increasing the preys' adhesion, we would expect the second explanation to be the most likely. 27,29,53 In any case, these extremely fine nanofibres have to balance the requirements of maximal adhesion with sufficient structural integrity as fibres, both to maintain their fibrillary form and to restrain prey. We found the silks to contain serine, hydroxyproline as well as charged lysine and polar amino acids, and these amino acids may be facilitating the structural integrity of the nanofibres.…”