Contents - Faperta

Transgenic Resistance to Insects: Interactions with Nontarget Organisms 351
potato crop (Riddick, Dively, and Barbosa, 1998). Feeding larvae of the coccinellid, C. sexmaculatus,
on H. armigera larvae reared on Bt-intoxicated diet results in slow growth of the
coccinellid larvae (Figure 11.3). However, the coccinellid grubs and adults feed on several
insects under fi eld conditions, and therefore, may not be exposed to high levels of Bt toxins
or only to prey of poor nutritional quality.
Larvae of C. carnea fed on pollen from transgenic maize did not complete development
on the pollen diet, although pollen was provided to the larvae for a limited period of time
(Pilcher et al., 1997). Larvae of C. carnea fed lepidopteran larvae (such as S. littoralis) reared
on maize expressing cry1Ab are affected adversely (Hilbeck et al., 1998a, 1998b, 1999;
Dutton et al., 2002). Predator larvae were also affected when fed pure activated Bt toxin in
artifi cial diet (Hilbeck et al., 1998b). Prey-mediated effects of transgenic plants have been
studied through intoxicated L. decemlineata eaten by C. maculata, with some reduction in
consumption rate and survival of C. maculata (Riddick and Barbosa, 1998). These studies
not only showed the direct toxicity of Bt toxins to the predators, but also revealed plantherbivore-natural
enemy interactions that contributed to increased mortality mediated by
insect-resistant transgenic plant fed prey that were not lethally affected by the transgenic
plants. However, further studies may be necessary to ascertain whether the adverse effects
were from the intoxicated prey or from the Bt toxin directly. Transgenic Bt sweet corn and
the foliar insecticides indoxacarb and spinosad are all less toxic to the most abundant
predators in sweet corn (C. maculata, Hippodamia axyridis Pallas, and O. insidiosus) than the
FIGURE 11.3 Effect of feeding Helicoverpa armigera larvae reared on Bt-intoxicated diet to the grubs of the
coccinellid predator Cheilomenes sexmaculatus (left) as compared to those fed on untreated artifi cial diet (right).