In this study, we evaluated in field trials the effects on non-target species, of transgenic corn producing the Cry1Ab toxin of Bacillus thuringiensis (Bt). In 1998, we collected Ostrinia nubilalis (Hübner) larvae from transgenic Bt corn (Novartis Hybrid 176) and non-Bt corn at four geographical sites. We found a significant variation in parasitism by the tachinids Lydella thompsoni (Herting) and Pseudoperichaeta nigrolineata (Walker) among sites, and more parasitism in non-Bt than in Bt fields. The Bt effect did not vary significantly among fields. In 1999, we performed a field experiment at two sites, comparing the temporal abundance of non-target arthropods in Bt corn (Monsanto Hybrid MON810) and non-Bt corn. The non-target insects studied included the aphids Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.) and Sitobion avenae (F.), the bug Orius insidiosus (Say), the syrphid Syrphus corollae (Meigen), the ladybird Coccinella septempunctata (L.), the lacewing Chrysoperla carnea (Stephens), thrips and hymenopteran parasitoids. For all species but one, the number of individuals varied greatly over the season but did not differ between the types of corn. The only exception was thrips which, at one site, was significantly more abundant in Bt corn than in non-Bt corn. However this difference did not remain significant when we took the multiple tests into account. Implications for pest resistance management, population dynamics and risk assessment are discussed.

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PAV, one of the luteoviruses inducing the barley yellow dwarf disease, greatly reduces yield of cereal crops and has been reported to cause reddening in several varieties of maize (Zea mays L.). However, there have been no reports that the virus causes significant reductions in size or yield of irrigated maize. Trials to assess the effect of PAV on maize yields were conducted for 3 yr with two hybrids (‘Déa’ and ‘Nobilis’) and two isolates of PAV (2t and L14). These two isolates differed in geographic origin and virulence on barley (Hordeum vulgare L.), but they multiplied similarly to wild isolates in leaves of maize hybrids. The virus was detected in maize leaves during the same period after inoculation in two out of three years. The reason for low levels of virus in leaves in the 1996 season may have been high temperatures (>30°C) following inoculation. Under these conditions, the virus was restricted to the roots for long periods. This blocking of virus migration and/or foliar multiplication was accompanied by less reddening, and there was almost no decrease in grain yield. High early leaf infection of the virus had little effect on the vegetative development of the hybrids (<10% reduction in plant height), but grain yield was between 15 and 20% lower for a production of 10 to 12 t ha−1 This drop in yield was due to fewer kernels of maize per ear, while the 1000 kernel mass was unaffected. The loss in yield was not affected by either the virus isolate or the maize hybrid, although the intensity of symptoms differed between hybrids. The data show that there are potential losses incurred by PAV on maize yield. Therefore, these findings justify the establishment of a breeding program.