Aspects of the biology and reproductive strategy of two Asian larval parasitoids evaluated for classical biological control of Drosophila suzukii

Abstract

Drosophila suzukii Matsumura (Diptera: Drosophilidae) is native to eastern Asia, but has established in Europe, North America and South America, where it is a pest of numerous berry and other small fruit crops. As a part of a classical biological control program, two larval D. suzukii parasitoids, Ganaspis brasiliensis Ihering and Leptopilina japonica Novković & Kimura (Hymenoptera: Figitidae), were imported from South Korea to a California quarantine for evaluation. Here, we report on aspects of their reproductive strategy, including egg maturation dynamics, host age preference and suitability, and life-time fecundity. Adult females of both species emerged with a high mature egg-load that peaked 1–2 days post emergence. Both parasitoid species preferred to attack young host larvae (1–2 day old), although host age did not affect the parasitoid offspring’s sex ratio or fitness (survival, developmental time and body size of female wasps). Held at 22 ± 2 °C with honey-water and D. suzukii larvae in artificial diet, as well as a constant source of adult males, G. brasiliensis adult females survived 17.7 ± 1.4 days and produced 98.3 ± 11.8 offspring per female, while L. japonica survived 18.7 ± 1.1 days and produced 107.2 ± 9.9 offspring per female. The proportion of female progeny decreased with increasing maternal age for both parasitoid species. Estimated demographic parameters were similar for both G. brasiliensis and L. japonica: net reproduction rate was 39.9 and 47.3, intrinsic rate of increase was 0.130 and 0.138, mean generation time was 28.5 and 28.1 days, and doubling time was 5.4 and 5.0 days, respectively. This information is being used to compare these exotic D. suzukii parasitoids and determine their value as potential biological control agents.