Causes and consequences of sex ratio variation in the parasitoid wasp Pelecinus polyturator

Abstract

Pelecinus polyturator (Drury) (Hymenoptera: Pelecinidae) is a parasitoid wasp of the larval stages of June beetles of the genus Phyllophaga (Coleoptera: Scarabaeidae). It is morphologically variable across its range throughout continental North and South America. This species is divided into two distinct populations: a northern population (southeastern Canada, and the United States east of the Rocky Mountains) and a southern population (northern Mexico to Argentina, excluding Chile). The area of Mexico between 23° N and 28° N is apparently uninhabited by the species and distinctly separates the two populations. The northern population is almost entirely made up of females, whereas the southern population is bisexual. In this study, we extract, replicate, and sequence DNA from P. polyturator specimens collected in localities of both the northern and southern populations. We then examine the resulting DNA barcodes for factors related to variation in sex ratio, including relatedness of the cox1 gene and the presence of symbiotic bacteria (Wolbachia). Analysis of cox1 relatedness suggests that there is a gradient of genetic variation throughout the southern population. Specimens from the northern population were found to be nearly identical. Wolbachia was present in both the northern and southern populations and was nearly identical in all positive specimens. This suggests that Wolbachia is not the cause of sex ratio variation in P. polyturator.