Life History Traits of <I>Helicoverpa zea</I> (Lepidoptera: Noctuidae) on Non-Bt and Bt Transgenic Corn Hybrids in Eastern North Carolina

Abstract

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.

Resistance of Trichoplusia ni Populations Selected by Bacillus thuringiensis Sprays to Cotton Plants Expressing Pyramided Bacillus thuringiensis Toxins Cry1Ac and Cry2Ab

“…The slower larval development of resistant T. ni on BollGard II plants indicates that, in the field, there may be asynchrony of mating between the T. ni populations from non-Bt cotton and BollGard II cotton plants. Slower larval development on Bt plants than on non-Bt plants has been reported for several insect species, based on both laboratory and field observations (44)(45)(46)(47)(48). Asynchrony of mating between insects from non-Bt plants and Bt plants in the field has been reported to be a factor that may affect the refuge strategy for resistance management (44,49).…”

Bacillus thuringiensis -toxin resistance management: Stable isotope assessment of alternate host use by Helicoverpa zea

“…Engineered cotton and corn cultivars produce a high dose of the Cry1A forms of Bt toxin relative to the toxin tolerance of some major insect pests such as Heliothis virescens (F.) and Ostrinia nubilalis, but not for Helicoverpa zea (commonly known as the bollworm, the corn earworm, or the tomato fruitworm), which has a naturally high tolerance for most Bt toxins (7)(8)(9). When plants do not produce a high dose of toxin for a specific pest, a very large refuge must be maintained to reach the 500:1 ratio (2, 10).…”

Comparative Production of <I>Helicoverpa zea</I> (Lepidoptera: Noctuidae) from Transgenic Cotton Expressing Either One or Two <I>Bacillus thuringiensis</I> Proteins with and without Insecticide Oversprays

“…Because larval numbers were similar between UT conventional and Bollgard cotton, either the Bt toxins negatively affected the pupation/eclosion process or the incidence of disease or parasitization may have been elevated within Bollgard cotton due to prolonged larval development. Storer et al (2001) reported that pupal mortality for bollworms that originated on Bt corn plants was elevated compared with those from non-Bt corn plants. Approximately 78% of large bollworm larvae in the UT conventional variety survived to the adult stage, whereas proportionately fewer (57%) made it to adult emergence in the UT Bollgard variety.…”