Population-scale laboratory studies of the effect of transgenic plants on nontarget insects

Studies of the effects of insect-resistant transgenic plants on beneficial insects have, to date, concentrated mainly on either small-scale 'worst cas e scenario' laboratory experiments or on field trials. We present a laborat ory method using large population cages that represent an intermediate expe rimental scale, allowing the study of ecological and behavioural interactio ns between transgenic plants, pests and their natural enemies under more co ntrolled conditions than is possible in the field. Previous studies have al so concentrated on natural enemies of lepidopteran and coleopteran target p ests. However, natural enemies of other pests, which are not controlled by the transgenic plants, are also potentially exposed to the transgene produc t when feeding on hosts. The reduction in the use of insecticides on transg enic crops could lead to increasing problems with such nontarget pests, nor mally controlled by sprays, especially if there are any negative effects of the transgenic plant on their natural enemies. This study tested two lines of insect-resistant transgenic oilseed rape (Brassica napus) for side-effe cts on the hymenopteran parasitoid Diaeretiella rapae and its aphid host, M yzus persicae. One transgenic line expressed the F-endotoxin Cry1Ac from Ba cillus thuringiensis (Bt) and a second expressed the proteinase inhibitor o ryzacystatin I (OC-I) from rice. These transgenic plant lines were develope d to provide resistance to lepidopteran and coleopteran pests, respectively . No detrimental effects of the transgenic oilseed rape lines on the abilit y of the parasitoid to control aphid populations were observed. Adult paras itoid emergence and sex ratio were also not consistently altered on the tra nsgenic oilseed rape lines compared with the wild-type lines.