Pupation Site Affects the Mating Success of Small but Not Large Female Bagworms, Oiketicus kirbyi (Lepidoptera: Psychidae)

Abstract

In Costa Rican oil palm plantations, apterous female bagworms, Oiketicus kirbyi, emerge three weeks before and greatly outnumber males. Mating success of females is limited by the low abundance of males, as is obvious by the large proportion of females which never get mated during their lifetime. In the competition for access to mates, large rather than small females and females pupating on highest sites have a proportionately greater mating success. In the present study, we tested the hypothesis that pupation on highest sites represents a size-specific adaptation of small, least attractive females to increase their mating success. Small and intermediate-sized females had a higher mating success on the apical than subapical section of upright leaves, whereas their mating success did not differ on the same two sections of horizontal leaves. Equally high mating success of large females on apical and subapical sections of all leaves indicates that large females effectively attract males, independently of their pupation site. Enhanced mating success of small females on apical sections of upright leaves suggests that females compensate for small size by pupating in sites most suitable for attracting males. Lack of preponderance of small females on apical sections of upright leaves, however, invalidates the hypothesis that pupation on higher sites represents a size-specific adaptation of small females to enhance their mating success. It suggests that selection of pupation sites by female larvae is influenced by additional factors other than mating success.