Does local habitat management or large-scale landscape composition alter the biocontrol services provided to pumpkin agroecosystems?

Abstract

Cucurbit crops are attacked by a pest complex that threatens production via direct feeding and disease transmission. The goals of this study were to quantify the amount of biocontrol service supplied to pumpkin fields and determine if this was affected by local habitat management or the surrounding landscape. Using sentinel eggs, we measured predation of squash bug, Anasa tristis, and spotted cucumber beetle, Diabrotica undecimpunctata howardi, by generalist predators. We found that predators significantly removed D. undecimpunctata howardi but not A. tristis eggs. The guild of predators found to attack D. undecimpunctata howardi included Araneae, Carabidae, Cricetidae, Entomobryidae, Formicidae, Gryllidae and Opiliones. A smaller, but overlapping guild of predators was found to attack A. tristis, which included Araneae, Cricetidae, Formicidae and Gryllidae. Formicidae was consistently the dominate predator of both pest species. We examined how the addition of either a non-native annual plant insectary of sweet alyssum, Lobularia maritima, or a diverse insectary planted with native perennial forbs and grasses influenced predator abundance, composition, or biocontrol services relative to a grass control. We found no difference in either the predator community feeding on pest eggs or the proportion of eggs that they removed from adjacent pumpkin fields. Larger-scale landscape composition did influence the amount of egg predation occurring in pumpkin agroecosystems, however, these relationships varied among pests and across years of the study. Biological control is commonly predicted to increase with landscape diversity and the amount of non-crop habitat present surrounding focal fields, yet we found that when landscape did influence egg predation it was agricultural landscapes supporting the highest egg removal. This study illustrates that patterns relating landscape and localized habitat management to crop pest predation are not constants, they can vary among years within a crop as well as among agricultural cropping systems.