Life history traits of Helicoverpa zea (Lepidoptera:
Noctuidae) on non-Bt and Bt transgenic corn hybrids in eastern North Carolina.
Storer NP, Van Duyn JW, Kennedy GG.
Department of Entomology, College of Agriculture and Life Sciences, North
Carolina State University, Raleigh 27695-7613, USA. nstorer@dowagro.com
Transgenic varieties of field corn that express the CrylAb B. thuringiensis (Bt)
toxin in ear tissue present the potential of reducing ear feeding by the corn
earworm, Helicoverpa zea (Lepidoptera: Noctuidae), and for reducing the size of
populations of the insect infesting other host crops. Life history parameters of
H. zea feeding on ears of conventional and Bt field corn varieties were measured
in field plots in eastern North Carolina in 1997 and 1998. Transformation events
investigated were Mon-810 and Bt-11. Bt corn was found to cause a steady
mortality of larvae during development, but permitted approximately 15-40%
survival to the prepupal stage compared with non-Bt corn. Mortality of prepupae
and pupae from Bt corn was also higher than from non-Bt corn, reducing overall
adult production by 65-95%. The larvae that did survive grew more slowly on Bt
than on non-Bt corn, and produced pupae that weighed 33% less. Pupation and
adult eclosion were delayed by 6-10 d by feeding on Bt corn ears. Corn varieties
expressing Bt in ear tissue have the potential to reduce H. zea ear feeding by
up to 80%, and the potential to reduce populations emerging from ear-stage corn
fields to infest cotton, soybean and other crops by around 75%. To have a
measurable effect on area-wide populations, Bt corn varieties would need to be
planted in large proportions of corn fields. Extensive planting of varieties
such as those tested here, having only moderate effects on H. zea, would raise
concerns about rapid evolution of resistance.