Effects of biological and environmental factors on sex ratio in Ascogaster quadridentata Wesmael (Hymenoptera: Braconidae), a parasitoid of Cydia pomonella L. (Torticidae)

The sex ratio in the natural population of most Hymenopteran parasitoids is 1 : 1. Females of these parasitoids, however, can regulate the sex of their offspring in response to environmental and biological factors. Under certain circumstances, this may lead to an overproduction of males, which can result in a very negative impact on any control program using these parasitoids. For these reasons, understanding the effect of these factors is very important. In this study, five biological and environmental factors known to affect sex ratio in parasitic Hymenoptera were investigated for Ascogaster quadridentata Wesmael, a parasitoid of Cydia pomonella L. Results showed that food, ambient temperature, and parasitoid age had significant effects on the sex ratio of the offspring of Hymenopteran parasitoids. The percentage of females decreased with lack of food, parasitoid age (when it became 10-days-old or older), and at low (15°C) and high (35°C) temperatures. The effect of host age and density, however, was not significant.

A study of codling moth (Cydia pomonella) parasitism by Ascogaster quadridentata in a derelict apple orchard

Ascogaster quadridentata (Hymenoptera Braconidae) is a codling moth parasitoid native to Europe and established in New Zealand following introductions from the UK in the 1930s Ascogaster quadridentata parasitises the eggs of codling moth and develops and overwinters throughout the larval period of the host finally emerging from the host larval cocoon in spring As a result of its slow development the parasitoid does not protect the fruit from larval feeding damage Codling moth larvae in overwintering cocoons concealed under bark on apple trees were collected from a derelict orchard in Upper Moutere Nelson Larvae (n117) were carefully extracted from their cocoons and introduced into rolls of corrugated cardboard to complete their development Eightyeight larvae were successfully reared and 37 of these (42) were parasitized by A quadridentata This result is similar to a limited number of other records for this parasitoid in New Zealand and indicates that A quadridentata assists in reducing high populations of codling moth in derelict orchards or wild apple trees which are the main source for codling moth infestations in nearby commercial orchards