Habitat manipulation of the apple orchard floor to increase ground-dwelling predators and predation of Cydia pomonella (L.) (Lepidoptera: Tortricidae)

Augmenting generalist predator populations in new apple (Malus domestica Bork) plantings could potentially aid in the establishment of balanced orchard ecosystems that are less susceptible to pest outbreaks. Habitat can be an important factor in retaining predators in a system and can affect predator efficiency. We investigated the potential of increasing a complex of generalist ground-dwelling predators and enhancing biological control in a young 'Golden Delicious' apple orchard through ground habitat manipulation. We modified the orchard floor with four comparative habitat treatments: (1) detritus-rich compost mulch layer, (2) detritus-free synthetic mulch layer, (3) herbicide-treated vegetation thatch, and (4) bare soil with vegetation hand-removed. Relative abundances of predators and alternative prey in the habitats were measured with pitfall trapping throughout the growing season. Predation was measured using sentinel Cydia pomonella larvae and directly observed in night experiments. Throughout the season, the compost mulch treatment consistently supported significantly greater densities of alternative prey resources for predators, and generalist predators were more abundant in the compost mulch than the other habitats. Predator complex abundance was positively correlated with increasing alternative prey availability in the compost mulch habitat. However, predation of C. pomonella was significantly lower in the compost mulch than in the herbicide-treated thatch habitat. Our study revealed that a prey-rich organic mulch can enhance ground-foraging generalist predators on the orchard floor, but habitat structure may be more important than alternative prey for predation of C. pomonella.