Factors affecting the parasitism rate and the number and sex ratio of offspring of Asecodes hispinarum Bouček (Hymenoptera: Eulophidae), a biological control agent of Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae)

Abstract

To optimise the production of Asecodes hispinarum Bouček (Hymenoptera: Eulophidae), a parasitoid of coconut leaf beetle, Brontispa longissima (Gestro) (Coleoptera: Chrysomelidae), some of the factors affecting rates of parasitism, number of offspring produced per host and sex ratio of A. hispinarum were investigated. The numbers and sex ratio of A. hispinarum offspring per host reduced significantly at extreme low humidity (30% relative humidity [RH]), but there was no significant effect on parasitism. Photoperiod had no significant effects on any of the life traits tested. A. hispinarum was able to reproduce via arrhenotoky, and while increasing the proportion of female parents increased the number of parasitoids produced, the proportion of female offspring decreased. Older females showed a lower rate of parasitism than young females, however, maternal age did not affect the number or the sex ratio of offspring. Increasing the number of hosts offered to a pair of parasitoids significantly increased the number of parasitised hosts but decreased the parasitism rate while the sex ratio of progeny was not affected. Present work showed that to maximise the production of female parasitoids, a parasitoid/host ratio of 1:1, using one-day old A. hispinarum at a female/male ratio of 3:1 and RH of at least 55% is recommended.