Modeling the effects climate change, plant resistance, herbivore virulence, and parasitism on the population dynamics of aphids and parasitoids in wheat and soybean

Authors: Hopper, Keith

Submitted to: Ecological Modelling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2023
Publication Date: 4/13/2023
Citation: Hopper, K.R. 2023. Modeling the effects climate change, plant resistance, herbivore virulence, and parasitism on the population dynamics of aphids and parasitoids in wheat and soybean. Ecological Modelling. 481. https://doi.org/10.1016/j.ecolmodel.2023.110376.
DOI: https://doi.org/10.1016/j.ecolmodel.2023.110376

Interpretive Summary: Invasions of pest insects are an increasing problem for agriculture. Introductions of natural enemies (parasitoids) from the regions of pest origin and breeding plants for resistance to invasive pests have been effective at reducing pest abundance and impact, while providing safe, sustainable alternatives to insecticides. However, parasitoids and resistance are likely to interact in their impact on pests, and climate change is likely to affect these interactions. I developed mathematical models, based on published experimental results, to test two hypotheses: (1) parasitoids can reduce abundances and frequencies of virulent aphids that can overcome plant resistance, (2) temperature affects the impact of parasitoids on virulent aphids, and (3) these interactions differ from crop to crop. I modeled two aphid-crop systems: soybean aphid on soybean, and Russian wheat aphid on wheat. In thes simulations, parasitoids reduced aphid numbers, and on wheat, also reduced the frequencies of virulent aphids capable of overcoming plant resistance. However, the reductions were greater on wheat than on soybean. Parasitoids actually increased the frequencies, while reducing the abundance, of virulent aphids on soybean when only susceptible soybean was present. Comparisons of population dynamics in southern versus northern U.S. locations suggest that climate change would lead to a decrease in the abundance and frequency of virulent aphids in northern locations.

Technical Abstract: Invasions of insects that become pests are an increasing problem for agriculture. Introductions of parasitoids from the regions of pest origin and breeding plants resistant to invasive pests have been effective at reducing pest abundance and impact, while providing safe, sustainable alternatives to insecticides. However, parasitoids and resistance are likely to interact in their impact on pests, and the abiotic environment, and in particular, climate change is likely to affect these interactions. Here I report mathematical models, parameterized with published experimental results, that we used to test the following hypotheses: (1) parasitoids can reduce abundances and frequencies of virulent aphids, (2) temperature regime affects the impacts of parasitoids on virulent aphids, and (3) the outcomes of these interactions vary with crop. I modeled the effects of parasitism on the interactions between plant resistance and aphid virulence for two systems: the soybean aphid, Aphis glycines, on soybean, and the Russian wheat aphid, Diuraphis noxia, on wheat. I studied parasitoids in the genus Aphelinus, species of which have a long association with biological control of invasive pests. In the simulations, parasitoids did reduce the abundances, and on wheat, the frequencies of virulent aphids capable of overcoming plant resistance. However, the reductions were greater on wheat than on soybean. Indeed, parasitoids actually increased the frequencies, while reducing the abundances, of virulent aphids on soybean when only susceptible soybean was present. If one is willing to accept that comparisons of population dynamics in southern versus northern locations indicate the likely effects of climate change in the northern locations, these simulations suggest that climate change would lead to a decrease in the abundance and frequency of virulent aphids in northern locations.