California's almond industry, valued at $2.3 billion per year, depends on the pollinator services of honey bees, although pollination by other insects, mainly solitary wild bees, is being investigated as an alternative because of recent declines in the number of honey bee colonies. Our objective is to model the movements of honey bees and determine the conditions under which they will forage in less favorable areas of a tree and its surroundings when other pollinators are present. We hypothesize that foraging in less favorable areas leads to increased movement between trees and increased cross pollination between varieties which is required for successful nut production. We use the Shigesada-Kawasaki-Teramoto model (1979) which describes the density of two species in a two-dimensional environment of variable favorableness with respect to intrinsic diffusions and intra- and interspecific interactions of species. The model is applied to almond pollination by honey bees and other pollinators with environmental favorableness based on the distribution of flowers in trees. Using the spectral-Galerkin method in a rectangular domain, we numerically approximated the two-dimensional nonlinear parabolic partial differential system arising in the model. When cross-diffusion or interspecific effects of other pollinators was high, honey bees foraged in less favorable areas of the tree. High cross-diffusion also resulted in increased activity in honey bees in terms of accelerations, decelerations, and changes in direction, indicating rapid redistribution of densities to an equilibrium state. Empirical analysis of the number of honey bees and other visitors in two-minute intervals to almond trees shows a negative relationship, indicating cross-diffusion effects in nature with the potential to increase movement to a different tree with a more favorable environment, potentially increasing nut production.

<p>There is an existing conflict thrust upon U.S. food production systems; optimize crop yield to provide sustenance to a growing population while minimizing ecological impacts of high-intensity agriculture. This balancing act is experienced by Indiana’s watermelon growers who must maintain marketability of a crop that is reliant on insect pollinators. The dependence on pollinators to produce yield means that growers have to consider the negative impacts pesticide applications may have on both the desired pest and non-target pollinators. Navigating these trade-offs must be considered not just in the watermelon fields, but the surrounding agricultural landscape that has become increasingly reliant on prophylactic insecticides to control pests. This dissertation work results from an intensive set of experiments replicating grower practices in experimental fields throughout Indiana to assess the relationships of pests, pollinators, and crop yield.</p> Beginning with a priming year in 2017, watermelon plots were planted within larger corn fields to replicate the agriculture landscape and provide a “snapshot” of typical environment. These plots were paired at multiple locations and provided a contrast between a conventional management system that replicates grower insecticide programs with an IPM approach that removes insecticide applications outside of those based on scouting recommendations. I found that, while pest abundance and damage was higher in IPM fields, the increased pollinator visits in IPM fields led to higher yields in watermelons while corn yield was unaffected by an absence of insecticide use. Managed pollinator hives were placed in these fields and IPM resulted in the colonies exhibiting greater weight gain, lower mortality, increased reproductive growth, and higher insecticide residue accumulation. Insecticide residues were found more frequently at higher levels in the leaf tissue, crop pollen, field soil, and honey bee-collected pollen taken from CM fields. Despite these findings, there was a variable effect of the surrounding land use on the quality of collected pollen or the insecticides gathered by pollinators. These experiments demonstrate that IPM is a viable set of practices for specialty crop growers in the Midwest; successfully monitoring insect pests and conserving pollination services from both managed and wild pollinators. These findings provide a comprehensive look at the effect of IPM practices not just on the a specialty crop, but to the surrounding agricultural landscape as well. An IPM approach can be implemented by growers to decrease non-target effects from insecticides while maintaining or even improving productivity and profitability.

Intensive agricultural systems have had several ecological effects on the surrounding ecosystem, including contributing to widespread pollinator declines. In order to help supplement bee communities and potentially improve crop production, we set out to study annual forb plantings adjacent to dry bean crops to determine the pollinator response to both plantings and any potential effects on dry bean yield. We found that annual forb plantings provided continual floral resources throughout the sampling period, which can support bees and their pollination services in agroecosystems. We also found cross-pollination had no effect on dry bean yield in Carrington and a negative effect in Hettinger, which could be due to methodological issues. While we did not observe a yield increase in dry bean production, the addition of annual forb plantings in agroecosystems could help support the local bee community, and potentially encourage pollination services in other crops that do benefit from insect pollination.

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