Effects of mating and oviposition delay on parasitism rate and sex allocation behaviour of Diaeretiella rapae (Hymenoptera: Aphidiidae)

Mating and oviposition complement each other in parasitoid reproduction; delay in either of these activities has disparate consequences for the fitness of the parasitoid. We investigated the effects of mating and oviposition delay on parasitism rate and progeny sex ratio in a parasitic wasp Diaeretiella rapae. Egg dynamics in the ovaries of females of different ages, and females which completed different numbers of oviposition bouts were also examined. Delay in mating and oviposition adversely affected reproductive performance of both male and female D. rapae. Delayed oviposition resulted in reduced parasitism rates in both mated and unmated females. The progeny sex ratio was female-biased, but the proportion of female offspring decreased towards the end of D. rapae life. Although females emerged with developed eggs, the egg load in the ovaries of unmated and naïve females initially increased then continuously decreased with age, suggesting partial resorption of eggs towards the end of a females life. Oviposition rate of unmated females was low before mating. The extent of mating delay experienced by females affected the sex ratio of their progeny, causing overproduction of males. Delayed mating did not affect the courting capacity of males, but reduced the number of their offspring and proportion of female offspring. The duration of copulation was longer in older males. The results of this study clearly indicate the importance of parasitoid age in biological control programmes, and suggests the use of 1–2 days old D. rapae for best results.

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► Female Diaeretiella rapae emerge with developed eggs.
► Oviposition delay resulted in decreased parasitism by D. rapae.
► Delay in mating did not affect courting but affected the reproductive capacity of male and female D. rapae.
► Mating delay caused overproduction of male D. rapae.
► One-two day old D. rapae adults could perform more efficiently than younger or older adults as biocontrol agents.