Person:

Canfield, Michael Ross

1. Crypsis is one of the main defences that insects use to avoid predators, and both the juveniles and adults of many geometrid moths are remarkable in their ability to blend into different host backgrounds. The larvae of Synchlora frondaria have two methods to achieve crypsis: phenotypic plasticity in colouration that enable them to hide more effectively on their host plants, and a self-decorating behaviour whereby the larvae camouflage themselves with materials from their host plants. 2. Larvae of Synchlora frondaria reared on three different host plants showed systematic differences in relative growth rate, survivorship and larval colouration. 3. Larval colouration varied across diet treatments in a way that was consistent with diet-induced phenotypic plasticity, and larvae also exhibited characteristic decorating behaviour on all three hosts. 4. Larvae showed highest survivorship on Heterotheca subaxillaris (Asteraceae), and had significantly higher relative growth rates on H. subaxillaris (Asteraceae) and Lantana camara (Verbenaceae) than on Bejaria racemosa (Ericaceae). 5. Synchlora frondaria provides an example of a species where both decorating behaviour and phenotypic plasticity in larval colouration produce a cryptic form that is remarkably responsive to its background.

Several Asian pierid butterflies exhibit a pattern of phenotypic plasticity whereby the wing surfaces are more melanized in the wet season than in the dry season. The wet season in the Indo-Australian regions where these species occur is warmer, so this pattern cannot be explained as an adaptation for thermoregulation. We propose an alternative hypothesis of facultative mimicry to explain this pattern. Species in the aposematic pierid genus Delias are widespread through Indo-Australia, and feed on host plants that are assumed to be toxic. The wet season forms of pierid species such as Appias lyncida, Prioneris thestylis and Cepora nerissa have darkened wing patterns that make them likely mimics of Delias species. Other species such as Ixias pyrene also have a wet season pattern that may benefit from its resemblance to Delias species. This hypothesis could be tested with experiments on the differential success of the seasonal forms under varying conditions. Facultative mimicry may represent a previously undocumented means by which insects can adjust their participation in mimetic relationships by using cues from their environment.