High susceptibility of Bt maize to aphids enhances the performance of parasitoids of lepidopteran pests

Abstract

Concerns about possible undesired environmental effects of transgenic crops have prompted numerous evaluations of such crops. So-called Bt crops receive particular attention because they carry bacteria-derived genes coding for insecticidal proteins that might negatively affect non-target arthropods. Here we show a remarkable positive effect of Bt maize on the performance of the corn leaf aphid Rhopalosiphum maidis, which, in-turn enhanced the performance of parasitic wasps that feed on aphid honeydew. Within five out of six pairs that Were evaluated transgenic maize lines were significantly more susceptible to aphids than their near-isogrenic equivalents, with the remaining pair being equally, susceptible. The aphids feed from the phloem sieve element content and analyses of this sap in selected maize lines revealed marginally, but significantly higher amino acid levels in Bt maize, which might partially explain the observed increased aphid performance. Larger colony densities of aphids on Bt plants resulted in an increased production of honeydew that can be used as food by beneficial insects. Indeed, Cotesia marginiventris, a parasitoid of lepidopteran pests, lived longer and parasitized more pest caterpillars in the presence of aphid-infested Bt maize than in the presence of aphid-infested isogenic maize. Hence, depending on aphid pest thresholds, the observed increased susceptibility of at maize to aphids may be either a welcome or an undesirable side effect. © 2007 Faria et al.