Mulch type and moisture level affect pupation depth of Rhagoletis mendax Curran (Diptera: Tephritidae) in the laboratory

Mulching can be beneficial for organic highbush blueberry production, but its effects on insect pests have received little attention. For pests that pupate in soil, depth may affect pupation success due to differences in temperature and moisture, mortality factors such as predation, or efficacy of controls such as insecticidal soil drenches. We examined how mulch type and moisture affect pupation depth for Rhagoletis mendax Curran (blueberry maggot), an important pest of blueberries. In laboratory studies, pupation depth was measured in wood waste compost, uncomposted pine needles, soil and sand, each at dry, field moisture levels and wet, 99% water holding capacity conditions. Pupation occurred more deeply but with greater variability in pine needle mulch compared to compost mulch, soil, or sand. Approximately 50% of maggots pupated on the surface of wet soil, however, maggots burrowed more deeply in wet than in dry pine needles. Moisture level did not significantly affect pupation depth in compost or sand. Some larvae unexpectedly escaped the stacks of cups used to assess pupation depth or died before forming a puparium. Less than 70% of stacks with dry pine needles contained pupae, and fewer pupae were recovered from wet than dry compost and soil. These results suggest that mulch material and/or moisture levels can have significant impacts on R. mendax pupation depth with potential implications for its management.