Introduction

Abstract

Sperm competition has been conceptualised, in the narrow sense, as a process of sexual selection defined as the competition, between the sperm of more than two males who have mated with the female, for fertilisation of the eggs in the female internal reproductive organs (Parker 1970). In insects, once a female has copulated, the sperm transferred from the male is stored and maintained unchanged in female sperm storage organs that have specialised morphology, mainly tissue, to provide both nutrition and a constant ionic environment for sperm survival throughout her lifespan (e.g., Villavaso 1975). Therefore, insect sperm must retain its fertilisation capacity throughout the lifespan of the female, and the females are able to fertilise eggs using the stored sperm for oviposition at any time. Typically, when a female oviposits, each egg passes down the oviduct via a special pouch near the exit of the sperm storage organs. Females can control the position of the eggs in their internal genitalia and have the ability to release exactly the adequate number of spermatozoa needed to fertilise the eggs (Walker 1980). The efficiency of sperm utilisation at fertilisation has been reported as being high because no sperm wastage occurs and a single spermatozoon is generally used to fertilise a single egg (Thornhill and Alcock 1983).