Effects of conventional or organic production systems on tritrophic interactions

Globally there is an increasing interest in less intensive agricultural practices and as a result organic agriculture is becoming more widely adopted and desired. However, to date there has been little vigorous scientific testing of the claimed benefits for this agricultural system, which needs addressing as food security becomes a significant challenge. Here we investigate whether organically grown cabbages (Brassica oleracea var capitata) are better defended against herbivorous insects (“chewing” Plutella xylostella and phloem-feeding Brevocoryne brassicae) than their conventionally grown counterparts. In particular we focus on the direct defences (e.g. glucosinolates) and indirect plant defences mediated through herbivore natural enemies. Tritrophic interactions, involving insect pests and their natural enemies, were investigated using cabbage plants grown using conventional or organic fertiliser treatments. The use of natural enemies such as parasitoids is a powerful biosensor for detecting chemical differences between plants and/or growing regimes.