Males of the tortricid moth Amorbia cuneana (Walsingham, 1879) shed their genital spines inside the female during copulation

Abstract

The genitalia of most insect species are composed of several structures whose functions are poorly understood in many cases. The deciduous genital spines (deciduous cornuti, DC) found on the endophallus of many species of Lepidoptera are a clear example of this problem. We performed two experimental studies with the western avocado leafroller Amorbia cuneana (Tortricidae), aimed at answering some basic questions about the biology of DC. We found that the number of DC shows positive allometry with male forewing length, indicating that larger males have disproportionally more DC than smaller males. Males, with very few exceptions, shed virtually all their DC in their first copulation. The position of DC within the female varies depending on time elapsed after copulation. We observed that mated males without DC are able to remate and transfer an ejaculate. Finally, we found that resource restriction during the last larval instar of males results in a reduction in the number of DC. We suggest that DC reduce the chances of recopulation of mated females, that the production of DC is physiologically costly, and that first copulations are more important for male fitness.