Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Networks of species interactions structuring ecological communities can provide insight into the functioning and stability of the community. Most existing insect interaction networks are created with species interactions over time pooled into a single, static network. This approach, while valuable, fails to take into account the dynamic nature of species interactions which can exhibit strong temporal variation due to species turnover, interaction rewiring, and changes in interaction strength. Additionally, most insect interaction networks to date have focused on plant-pollinator systems, while very few networks of host plants, herbivores, and parasitoids have been created. Parasitoids of lepidopteran agricultural pests can serve as effective biological control agents to reduce crop damage; therefore, an understanding of how species interact over time is imperative for making informed decisions about crop and integrative pest management strategies. We aimed to determine how species interactions between host plants, caterpillars, and parasitoids in an agroecosystem changed over time. We performed bi-weekly caterpillar surveys of different brassica crop varieties. We sampled a variety of host life stages because host susceptibility to parasitoids has been shown to change across ontogeny, and parasitoids are often specific in the life stages they can attack. Collected caterpillars were brought back to the lab and reared until an adult moth, butterfly or parasitoid emerged. We created interaction networks and examined interaction turnover across the growing season and between years.
Results/Conclusions We found that caterpillar diet breadth was similar for all species. Parasitoids were highly host-specific, and therefore were consistently linked to the same caterpillar species. Additionally, the abundance of caterpillar and parasitoid species varied across the growing season and between years. In 2019, 57% of the caterpillar species and 75% of the parasitoid species were present across the season. In 2020, 50% of the caterpillar species and 67% of the parasitoid species were present across the season. However, in both years the strength of the interactions between hosts and parasitoids changed across the season. 78% of the caterpillar species and 83% of the parasitoid species were present in both years. The strength of the host-parasitoid interactions was consistent between years. Overall, we found that species turnover, as opposed to interaction rewiring, was the primary driver of within-season interaction turnover. While overall interaction turnover was low, the strength of interactions between hosts and parasitoids was highly variable, which has implications for understanding how effective biological control agents may be during different parts of the season.
Results/Conclusions We found that caterpillar diet breadth was similar for all species. Parasitoids were highly host-specific, and therefore were consistently linked to the same caterpillar species. Additionally, the abundance of caterpillar and parasitoid species varied across the growing season and between years. In 2019, 57% of the caterpillar species and 75% of the parasitoid species were present across the season. In 2020, 50% of the caterpillar species and 67% of the parasitoid species were present across the season. However, in both years the strength of the interactions between hosts and parasitoids changed across the season. 78% of the caterpillar species and 83% of the parasitoid species were present in both years. The strength of the host-parasitoid interactions was consistent between years. Overall, we found that species turnover, as opposed to interaction rewiring, was the primary driver of within-season interaction turnover. While overall interaction turnover was low, the strength of interactions between hosts and parasitoids was highly variable, which has implications for understanding how effective biological control agents may be during different parts of the season.