The effects of allelochemical transfer on the dynamics of hosts, parasitoids, and competing hyperparasitoids

Allelochemicals produced by plants may be ingested by herbivorous insects and transferred to higher trophic levels with potentially deleterious effects. We develop a system of differential equations to investigate the effect of the transfer of allelochemicals, such as nicotine, on the population dynamics of a system of hosts, parasitoids, and two competing hyperparasitoids that attack different life stages of the parasitoids. We find both somewhat deleterious effects of nicotine on the larvae-attacking hyperparasitoids and increased attack rates for the pupae-attacking hyperparasitoids can promote coexistence. We also use an evolutionary game-theoretic approach to determine the optimal distribution of hyperparasitoid attacks among nicotine-producing and nicotine-free plants. With strong deleterious effects of nicotine and increased attack rates for the pupae-attacking hyperparasitoid, we find both species attack parasitoids on the nicotine-free plant but only pupae-attacking hyperparasitoids attack parasitoids on the nicotine-producing plant. Recommendations for Resource Managers: In the absence of nicotine and with equal attack rates, the larvae-attacking hyperparasitoids will exclude pupae-attacking hyperparasitoids due to the advantage of attacking an earlier life-stage of the parasitoid. Coexistence of larvae- and pupae-attacking hyperparasitoid species can occur when the pupae-attacking species has the advantage of a higher oviposition rate and/or when the larvae-attacking species suffers increased mortality due to nicotine. If mortality rates of larvae-attacking hyperparasitoids due to nicotine become too large, they are unable to persist. The population dynamics of systems incorporating multiple trophic levels are complex and intertwined. The presence of allelochemicals such as nicotine in the first trophic level may impact the observed diversity of hyperparasitoid species in the fourth trophic level.

Automated summary

The study explores the impacts of allelochemicals from plants on the population dynamics of hosts, parasitoids, and hyperparasitoids. Findings suggest both detrimental effects and increased attack rates can promote coexistence. The allocation of hyperparasitoid attacks between nicotine-producing and nicotine-free plants can impact species diversity at the fourth trophic level.