What controls the puppets? 20-hydroxyecdysone may not drive manipulation in Leucauge spiders

Abstract Parasites frequently manipulate host behavior to increase their own fitness, but the proximal mechanisms underlying these manipulations remain poorly understood. In interactions between polysphinctine parasitoid wasps and spiders, hosts are induced to build modified and more resistant webs (cocoon webs). This construction is currently attributed to the activation of the host's innate ecdysis mechanism, based on the cocoon web's similarity to spider molting webs and the association with elevated levels of the hormone 20-hydroxyecdysone (20E) in Araneidae species. However, the only empirical evidence of 20E enhancement is taxonomically restricted, limiting generalization. In this study, we investigated this ecdysis-based manipulation mechanism in a Tetragnathidae spider host. Examining the interaction between the spider Leucauge volupis (Keyserling, 1893) and the polysphinctine wasp Hymenoepimecis cameroni (Townes, 1966), we compared the architecture of normal, molting, and cocoon webs of the spider, and quantified 20E levels across the spider's group. Cocoon webs shared traits with molting webs, such as the absence of sticky spirals and increased reinforced radii. However, contrary to expectations, 20E levels were not elevated in behaviorally altered spiders compared with the other groups. Therefore, although cocoon webs resemble molting webs, ecdysone does not appear to be the proximate trigger of host manipulation in this system, suggesting that their structural similarity arises from alternative physiological or behavioral pathways yet to be identified.