Effects of Bacillus thuringiensis Transgenic Corn on Corn Earworm and Fall Armyworm (Lepidoptera: Noctuidae) Densities

Abstract

We examined 17 pairs of near-isogenic hybrids of Bacillus thuringiensis (Bt) (176, Mon810, and Bt11) and non-Bt corn, Zea mays L., to examine the effects of Bt on larval densities of Helicoverpa zea (Boddie) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) during 2 yr. During ear formation, instar densities of H. zea and S. frugiperda were recorded for each hybrid. We found that H. zea first, second, and fifth instar densities were each affected by Mon810 and Bt11 Bt corn but not by 176 corn. Surprisingly, first and second instars were found in higher numbers on ears of Mon810 and Bt11 corn than on non-Bt corn. Densities of third and fourth instars were equal on Bt and non-Bt hybrids, whereas densities of fifth instars were lower on Bt plants. S. frugiperda larval densities were only affected during 1 yr when second, and fourth to sixth instars were lower on ears of Mon810 and Bt11 hybrids compared with their non-Bt counterparts. Two likely explanations for early instar H. zea densities being higher on Bt corn than non-Bt corn are that (1) Bt toxins delay development, creating a greater abundance of early instars that eventually die, and (2) reduced survival of H. zea to later instars on Bt corn decreased the normal asymmetric cannibalism or H. zea-S. frugiperda intraguild predation of late instars on early instars. Either explanation could explain why differences between Bt and non-Bt plants were greater for H. zea than S. frugiperda, because H. zea is more strongly affected by Bt toxins and more cannibalistic.

Attack and defense movements involved in the interaction of Spodoptera frugiperda and Helicoverpa zea (Lepidoptera: Noctuidae)

“…Other studies involving cannibalism and intraguild predation of this species in the presence of Bt protein (Cry1Ab) in maize indicated reduced survival of H. zea in late instars on Bt maize, which decreases the regular rates of cannibalism and the H. zea -S. frugiperda intraguild predation of late instars on early instars. A reduction in cannibalistic behavior of H. zea might increase the survival of larvae in multiple infestations of Bt maize ears (Chilcutt et al 2007). Negative effects of Cry1Ab protein in H. zea behavior were also observed in an intraguild interaction study involving this species, Striacosta albicosta (Smith) (Lepidoptera: Noctuidae), and Ostrinia nubilalis (Hübner) (Lepidoptera: Noctuidae) (Dorhout and Rice 2010).…”

Cross-Pollination of Nontransgenic Corn Ears With Transgenic Bt Corn: Efficacy Against Lepidopteran Pests and Implications for Resistance Management

“…This was demonstrated by Chilcutt and Tabashnik (2004), where kernels of non-Bt plants in an adjacent refuge area near Bt11 and Mon810-expressing plants, had Cry1Ab toxin concentrations that were 45 and 43% less than the adjacent Bt11 and Mon810 plants, respectively. For H. zea, corn plants with Bt11 and Mon810 events expressing Cry1Ab toxin do not provide a high dose, deÞned as a 25ϫ higher dose than is necessary to provide 99% mortality of the most susceptible life stage in a laboratory bioassay; this is true even with maximum Cry1Ab expression in the ear, allowing larval survival on ear tips (Horner et al 2003, OÕRourke and Hutchison 2004, Chilcutt et al 2007). Subsequently, even higher levels of survival are observed under the cross-pollination scenario (Tables 1 and 2).…”

Susceptibility of <I>Helicoverpa armigera</I> (Lepidoptera: Noctuidae) to Cry1Ac and Cry2Ab2 Insecticidal Proteins in Four Countries of the West African Cotton Belt

“…it should not be surprising that some levels of cross-resistance could exist between Cry1F and Cry1A.105 because of the association in the gene structures of the 2 proteins. Studies have shown that S. frugiperda was somewhat tolerant to the single gene Cry1Ab corn hybrids (US EPA 2001b;Chilcutt et al 2007;Hardke et al 2011;Huang et al 2011). In addition, Cry1Ac usually shares similar binding sites with Cry1Ab in the insect midgut membranes (Ballester et al 1999;Ferré & Van Rie 2002;Hua et al 2001;Tan 2010) and thus Cry1Ab resistance is often found to be cross-resistant to Cry1Ac in many insect species (Tabashnik et al 1994;Ferré &Van Rie, 2002;Rang et al 2004;Siqueira et al 2004;Wu et al 2009;Pereira et al 2010;Tan 2010;Crespo et al 2011;Zhang et al 2013).…”

“…Fall armyworm, Spodoptera frugiperda (J. E. Smith), is an important pest of corn in both North and South America (Pashley et al 1985;Pashley 1986;Buntin et al 2004;Chilcutt et al 2007). Several studies have evaluated the field efficacy of first generation single gene Bt corn products (e.g.…”