THE EFFECTS OF GROUND-FLOOR MANAGEMENT ON BLUEBERRY MAGGOT (RHAGOLETIS MENDAX CURRAN) AND PREDATORY BEETLES IN HIGHBUSH BLUEBERRIES

Abstract

There is very low tolerance for blueberry maggot (Rhagoletis mendax Curran) in blueberries making it a serious pest in eastern North America. Control is focused on eliminating flies with insecticides before oviposition in fruit. Organic mulches may improve highbush blueberry production, but their effects on this pest are largely unknown. The research in this thesis evaluated compost and pine needle mulches on blueberry maggot (mature maggots, pupae, emerging flies) and predatory beetles that may consume these stages.

Mulches affected fly emergence and maggot pupation. Fly emergence was reduced by 80-100% and delayed ~8 days from pupae covered with 20 cm of pine needles compared to 1 cm of soil. Emergence from 20 cm of compost was lower in wet conditions, and 5 cm of mulch did not limit emergence in the field. Pupation at increased depth reduced emergence because flies did not eclose or, if eclosed, were unable to crawl to the surface. The delay was likely due to lower temperatures at depth. No flies emerged from 1 cm in pine needles in the field probably due to high temperatures. In the laboratory, maggots pupated more deeply in pine needles than other substrates, but ~30% did not pupate in dry pine needles. Saturated soil caused ~50% of maggots to pupate on the surface.

Mulching altered beetle diversity and activity/density and affected beetle predation on maggots and pupae. Compost plots in a highbush blueberry field attracted predatory carabids and staphylinids, although some staphylinids were frequent in pine needles and phytophagous carabids preferred unweeded compost plots. Attraction to compost, particularly for Pterostichus melanarius (Illiger), was due primarily to higher prey densities - earthworms and millipedes - than other treatments. This beetle consumed some maggots or pupae in soil or compost, but predation rates decreased when alternative prey was abundant.

Blueberry bushes in weedy compost plots attracted many flies, but infestation rates were higher in composted bushes only in the year mulch was applied. Overall, thick mulching with pine needles contributes most significantly to blueberry maggot management. Future research should explore integration of mulch with other tactics for R. mendax control.