Abstract
Non-crop habitat adjacent to crops may be important for enhancing the activity of natural enemies in crops. However, it is not always clear whether natural enemies that are active in non-crop habitats actually contribute to pest suppression in adjacent crop habitats. We hypothesised that parasitic wasps that utilise the same hosts can be segregated between crop and non-crop habitats in an agro-ecosystem. We tested this hypothesis using the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), in vineyards and adjacent native vegetation. We experimentally measured the parasitism rate of larval E. postvittana at six and eight sites in both vineyards and the adjacent native vegetation in two consecutive years. Wild larval Tortricidae were also collected at each experimental site to assess their diversity and related parasitoids. Parasitised hosts were then identified using a PCR-based protocol to examine the parasitoids’ host ranges. The parasitoid Therophilus unimaculatus (Turner) (Hymenoptera: Braconidae) was most active in non-crop native vegetation, whereas Dolichogenidea tasmanica (Cameron) (Hymenoptera: Braconidae) parasitised the most larvae in vineyards. Parasitism of E. postvittana by D. tasmanica was higher on grape than on plantain, which indicates that host plants influence activities in different habitat. Both species shared the same range of tortricid hosts. Overall, our results indicate the two key parasitoids that attack E. postvittana differ in their pattern of habitat use. The native vegetation adjacent to crops may not enhance the activity of some natural enemies for pest control in an agricultural ecosystem.
Highlights
Modern agriculture production has intensively reduced noncrop habitat areas and simplified agriculture landscapes
Three parasitoid species were recovered from the larvae placed on plants: D. tasmanica, T. unimaculatus and Phytodietus celsissimus (Turner) (Hymenoptera, Ichneumonidae)
The contrast for parasitism by D. tasmanica between vineyard and adjacent vegetation was statistically significant in the split– split-plot analysis (F1, 10 = 6.67, P = 0.027)
Summary
Modern agriculture production has intensively reduced noncrop habitat areas and simplified agriculture landscapes. The abundance, activity or impact of natural enemies at the boundary of crop and non-crop habitats, the so-called ‘edge effects’, is often higher than that in field interiors (Duelli et al 1990; Dyer and Landis 1997; Thies and Tscharntke 1999; Rand et al 2006). This could be due to the proximity of alternative resources in the adjacent habitats (Rand et al 2006). It is necessary to fill this gap and to explore a possible mechanism explaining compartmentalization of trophic networks in semi-natural and crop habitats
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