Host plant exodus and larval wandering behaviour in a butterfly: diapause generation larvae wander for longer periods than do non‐diapause generation larvae

Abstract

1. Prior to pupation, lepidopteran larvae enter a wandering phase lasting up to 30 h before choosing a pupation site. Because stillness is important for concealment, this behaviour calls for an adaptive explanation.2. The explanation most likely relates to the need to find a suitable pupation substrate, especially in terms of shelter from predation, and given that many predators and parasitoids use host plants as prey-location cues, mortality probably decreases with distance from the host plant. Hence, remaining on the host includes a long-term risk, while moving away from the host introduces an increased risk during locomotion.3. Bivoltine species that overwinter in the pupal stage produce two kinds of pupae; non-diapausing pupae from which adults emerge after 1-2 weeks, or diapausing pupae that overwinter with adults emerging after 8-10 months.4. Given the hypothesis of distance-from-host-plant-related predation, this should select for phenotypic plasticity with larvae in the diapausing generation having a longer wandering phase than larvae under direct development, if there is a trade-off between mortality during the wandering phase and accumulated mortality during winter.5. Here this prediction is tested by studying the duration of the wandering period in larvae of the partially bivoltine swallowtail butterfly, Papilio machaon, under both developmental pathways.6. The results are in agreement with the predictions and show that the larval wandering phase is approximately twice as long under diapause development. The authors suggest that the longer duration of the wandering phase in the diapause generation is a general phenomenon in Lepidoptera.

Ontogeny of sexual size dimorphism revisited: Females grow for a longer time and also faster

“…In the course of the 5th (last) instar, the larvae were weighed daily until cessation of feeding (the beginning of the wandering stage; e.g. [47]). This allowed us to record the maximal larval mass, and the day on which it was achieved.…”

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

“…For example, many species burrow into the ground to pupate, which offers a refuge from the predators preying above the ground such as birds [17]. Before individuals enter the pre-pupal stage and start to spin their cocoon, they often disperse from their larval host plant or food source [9,24,38,39]. Staying close to the host plant can increase the risk of being detected by natural enemies that often use the host plant as a cue to locate their potential prey [13,40].…”

“…Lepidopteran larvae have a wandering phase prior to pupation when larvae move away from their host plant while seeking a suitable substrate for pupation [38]. In the European swallowtail butterfly, Papilio machaon, this wandering phase is longer in the overwintering generation, which has a longer pupal stage, in comparison to larvae that are under direct development (non-overwintering larvae), which have a pupal stage of only one to two weeks.…”

Extra molting, cannibalism and pupal diapause under unfavorable growth conditions in Atrophaneura alcinous (Lepidoptera: Papilionidae)

“…Moreover, if an individual who pupates under diapause at a location away from other conspecifics, cannibalistic attack is unlikely. Wiklund et al (2017) suggested that individuals of Papilio machaon who hibernate disperse further than those who do not diapause to escape from host-related predation. In nature, not only the balance between density and food conditions, but also the ability to disperse before pupation could be important for the survival of diapausing pupae in A. alcinous.…”