Effects of mulches and weeds on predators (Carabidae and Staphylinidae) and their potential prey in highbush blueberries

Insects of potential benefit to agriculture may respond to farming practices by increasing in abundance and diversity. In this study, we investigated effect of compost (from papermill biosolids) or pine needle mulch versus no mulch and weeding versus no weeding in plots in highbush blueberries near Rawdon, Nova Scotia, Canada. Pitfall traps were used to collect Carabidae and Staphylinidae from late July to late September in 2008 and 2009. Weed growth, temperature, and moisture in plots were also monitored. Allyl-isothiocyanate was used in 2009 to determine abundance of potential food items of common carabids. Carabids were captured in significantly greater numbers in compost due to abundant Pterostichus melanarius Illiger. Small earthworms, a prey item of this species, were also significantly more abundant in compost in late July in 2009. Captures of carabids increased from 2008 to 2009 due mainly to omnivores (Dicheirotrichus cognatus (Gyllenhal), Harpalus rufipes (DeGeer), Anisodactylus spp., Amara spp., Harpalus somnulentus Dejean, Pseudamara arenaria (LeConte)) in unweeded compost. These plots became significantly weedier between years. Greater temperature variation and drier conditions in pine needles may explain lower carabid captures even though some potential prey items were abundant. Final analysis of staphylinid captures is pending identification of all specimens. Stenus spp. were frequently captured in all plots, whereas Anotylus rugosus (Fabricius) and Xantholinus linearis (Olivier) were captured primarily in compost. Overall, compost caused increased abundance of soil dwelling organisms, promoted weed growth and was favored over pine needles and soil by many carabids and some staphylinids.