Edge Effects and Spillover Effects of Natural Enemies on Different Habitat Interfaces of Agricultural Landscape

Abstract

A majority of empirical tests have succeeded to support the hypothesis of edge effects and spillover effects. However, the two hypotheses tested in agro-ecosystems were rare. In order to discover edge effects and spillover effects on natural enemy’s populations of wheat aphids, we designed 5 different habitat interfaces including wheat-alfalfa, wheat-tree land, wheat-range, wheat-crop and wheat-bare land in Northwest of China. The biological control of natural enemies for wheat aphids were analyzed which aims to conduct habitat management in agricultural landscapes. We studied edge effects and spillover effects of natural enemy’s population and distribution through barber traps, net sweeping and clapper collection. Results showed that non-crop was important resource pool of natural enemies especially in alfalfa habitat, tree land and range habitat. Populations and communities of natural enemies in non-crop habitat played an important those role in biological control of wheat aphids. Communities of natural enemies (parasitoids and predators) in alfalfa were the same as those in wheat fields. In interface of alfalfa-wheat, spillover effects obviously exist. A majority of natural enemies (spiders and carabid beetle) immigrating from alfalfa habitat spread into wheat field and suppressed wheat aphids to a great extent. In interfaces of wheat-tree land and wheat-range, edge effects obviously exist. The biodiversity of natural enemies was higher in the interfaces than the inside of habitat. Hosts could be found in wheat habitat. Flowers, nectar and refuges could be found in non-crop habitat. Populations of natural enemies were larger in interface of wheat and non-crop than in other regions. However, crop habitat and bare land could play an important role in biological pest control of cereal aphids. The scale of edge effect was about 30 m below which natural enemies’ populations were more abundant than those in other regions. All these results can be applied in agricultural landscape design which aims at biological control and provided important theoretical principles, and also supplied new ways and methods for pest population control.