The Role of Substrate Variation in Leaf Selection and Reproduction of Megachile Rotundata (Fabricius) (Hymenoptera PDF Download

Author: Margaret Rei Scampavia
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ISBN: 9780355763522
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Languages : en
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Book Description
Bee visitation benefits reproduction of most flowering plants, including crop species. Bee populations depend on nesting resources for reproduction. Most bee species excavate nests in the soil, although many species utilize above ground cavities. My dissertation examines effects of bee nest substrate variation on nest material selection and potential reproductive consequences. Chapter One evaluates the impact of foliar insecticide residues on Megachile rotundata. M. rotundata, cavity-nesting bees with nests lined with leaf cuttings, are commercially managed in North America for alfalfa pollination. In cages with uncontaminated floral resources, I examined the effect of chlorpyrifos, an organophosphate used in alfalfa pest control, on M. rotundata leaf preference and reproduction. The number of adult offspring per female did not differ between treatments. While females provisioned fewer cells in cages with treated leaves, offspring mortality was greater in cages with untreated leaves. In a choice assay, preference for treated leaves increased with days from chlorpyrifos application. Chapter Two describes the effects of tillage, drip irrigation, and presence of the pyrethroid insecticide esfenvalerate on nest site selection by native soil-nesting bees in California. I compare nest incidence and nesting bee density between treatments in an experimental matrix of farming practices. Irrigation positively influenced nest initiation and bee density. Combined irrigation and tillage had the greatest positive effect. Esfenvalerate application did not affect nesting rates. Lasioglossum (Dialictus) spp. were the most abundant nesting bees, although we also reported results for Halictus ligatus, H.tripartitus, Melissodes tepida, and Svastra obliqua expurgata. Bee species responded differently to variations in edaphic properties. L. (Dialictus) spp. responded positively to soil moisture and negatively to soil hardness. Low nesting rates in tilled, dry soils suggest a lower threshold of compaction necessary for nest structural integrity. Chapter Three reviews the literature on the effects of abiotic factors on nest site preference of soil-nesting bees. Though most studies described conditions at nest sites with no statistical analysis, this review builds an understanding of bee nesting behavior in a range of conditions. The literature suggests bee preferences for irregular surfaces, compact and warmer soils, and soil moisture. Reported nest sites of smaller bees had less bare ground and soils with higher clay content than reported nest sites of larger bees. Study designs influenced reported responses of bees to bare ground and soil hardness. Inferring nest site preference from landscape or descriptive studies requires careful interpretation. Factors influencing nest locatability and tradeoffs between excavation ease versus structural integrity likely determine nest site suitability. My dissertation demonstrates that variation in substrates affects nest site preference and reproduction of bees. Agricultural intensification and human-induced climate change differentially affect nest site availability for different bee taxa. My research can be used to formulate testable predictions of mechanisms underlying bee abundance at the landscape level and responses to disturbance. These findings can inform both predictions of nest site preferences of soil-nesting bee species with undescribed nests as well as agricultural management decisions to promote bee pollination.