Corn leaf aphid (Hemiptera: Aphididae) and mycotoxin threats in transgenic maize

Abstract

A study to measure corn leaf aphid, Rhopalosiphum maidis (Fitch) abundance in corn rootworm-, Diabrotica spp., resistant hybrids (Pioneer 37N68) compared to conventional near-isoline maize hybrids (Pioneer 36V51) was conducted in Brookings South Dakota, during 2009 and 2010. This study investigated the potential effects of aphid abundance might have on mycotoxin risk.  Although aphids would not directly transmit the disease, the possibility exists that their presence may attract other insects that increase the risk of mycotoxin possibilities.    To induce potential outbreaks of R. maidis, carbaryl insecticide was applied at 1.12 kg[AI]/ha in half the plots on 10 July to eliminate beneficial arthropods and thus trigger later-season aphid resurgence. Aphid counts from whole-plant sampling were conducted on two week cycles from 10 August through 29 September. Aphid populations responded to the removal of predators and there were significantly more R. maidis found during sampling periods in treated conventional hybrid and Cry3Bb1 treatments. Additionally, we found greater aphid abundance in Cry3Bb1 plots over the near-isoline hybrid, irrespective of carbaryl treatments. The insect resistant hybrid was possibly more attractive to aphid colonization because it was not stressed from insect damage and withstood drought stress better than the near-isoline hybrid. Although concentrations of mycotoxins sometimes exceeded the maximum tolerable daily intake for humans, there was not a consistent correlation between aphid abundance and mycotoxin concentrations.