Competition between parasitoids of the cabbage seedpod weevil: effects on sex ratios and consequences for biological control

In any biological control program, it is important to have an in-depth knowledge of the ecosystem. Competition between natural enemies can have unpredictable effects, potentially disrupting biological control of the pest in question. Trichomalus perfectus and Mesopolobus morys are two parasitoids of the cabbage seedpod weevil. Both are candidates for introduction as classical biological control agents in Canada. I examined the effects of intra- and interspecific parasitoid competition in field and laboratory experiments. I found that a multiple-species introduction would not be more effective at controlling pest populations than a single-species introduction. I also found T. perfectus produced a female-biased offspring sex ratio in response to intraspecific competition. Using a theoretical approach, I explored how this shift might affect parasitoid-host population dynamics and biological control, incorporating the influence of increased virginity in the parasitoid population.