Spatial and temporal patterns of crop rotations and their impact on squash bee (Peponapis pruinosa) abundance in the Sacramento Valley of California

Agricultural landscapes dominated by annual crop rotations are highly dynamic. If a species is mobile and able to track its resources, then the scale and history of crop rotations may contribute to the abundance of that species at a given place and time. The squash bee (Pepopnapis pruinosa) is a specialist, annual, solitary ground nesting bee. It collects pollen only from Cucurbita sp. (e.g. squash and pumpkins) and nests in or near Cucurbita sp. fields. To explore the role of spatiotemporal connectivity (i.e. how connected a focal Cucurbita sp. field is to surrounding Cucurbita sp. fields through time) in a highly dynamic landscape I sampled squash bee abundance at 25 Cucurbita sp. fields that spanned a spatiotemporal connectivity gradient in the Sacramento Valley of California. I used GIS data provided by the Department of Pesticide Regulation and conducted grower interviews to determine where Cucurbita sp. fields were located the previous year. General linear models that included distance to nearest 2009 Cucurbita field best explained 2010 squash bee abundance. Field management practices (e.g. organic or conventional) and percent natural habitat within 2km of the field (i.e. the estimated foraging range of P. pruinosa) were not important explanatory variables. This study suggests that spatiotemporal connectivity may be important in determining squash bee abundance in agricultural landscapes dominated by annual crop rotations.