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Agroecosystems are species-poor in comparison to natural ecosystems and this may lead to an increased susceptibility to pest outbreaks. Pesticides prevent pest outbreaks; however, they threaten human, non-human, and environmental health. Increasing plant species diversity has been proposed as an alternative strategy. Increasing plant species richness may reduce herbivore abundance because herbivores are less efficient at finding preferred plant species when surrounded by non-preferred species (Resource Concentration Hypothesis) and/or because predatory insects that consume herbivores are more efficient and/or abundant in species-rich systems (Enemies Hypothesis). We established a forage crop diversity experiment using tall fescue (Festuca arundinacea), orchardgrass (Dactylis glomerata), alfalfa (Medicago sativa), and white clover (Trifolium repens). Three levels of plant species richness were created – each species in monoculture, each possible biculture, and all four species together. In the summer of 2018, we sweep sampled the plots weekly for five weeks and recorded the abundance of all insects collected. Our results suggested that, in our system, some herbivores respond negatively to increased plant diversity and overall, herbivore load (total number of insects / plant biomass per m2) decreased with increasing diversity, supporting the notion that increased plant diversity is a viable alternative pest management strategy. We conducted further statistical analyses on taxonomic groups, specifically at the family level, and herbivore diet breadth but found no relation between these factors and herbivores’ response to plant diversity.
Altmire, Gabriella R., "Effect of Plant Biodiversity on Insect Pests in a Forage Agroecosystem" (2019). Biology Honors Papers. 30.