Contents - Faperta

354 Biotechnological Approaches for Pest Management and Ecological Sustainability
transgenic sugarcane expressing GNA. In the second generation, adult longevity was
reduced by three days, adult size by 5%, and egg load by 24%. Neither the fi tness of females
of Aphidius ervi (Haliday) nor the sex ratio of the progeny was affected when reared
on aphids fed on transgenic plants expressing OCIDELTAD86 for nematode resistance
(Cowgill, Danks, and Atkinson, 2004). There are no detrimental effects of the transgenic
oilseed rape (expressing cry1Ac and OC-I) on the ability of the parasitoid, Diaeretiella rapa
(McIntosh) to control aphid, M. persicae populations. Adult parasitoid emergence and sex
ratio were not altered on the transgenic oilseed rape as compared with the nontransgenic
plants (Schuler et al., 2001). Bt oilseed rape caused 100% mortality of a Bt-susceptible strain
but no mortality of the Bt-resistant P. xylostella strain NO-QA (Schuler et al., 2004). Cotesia
plutellae (Kurdjumov) eggs hatched, but premature host mortality did not allow C. plutellae
larvae to complete their development in Bt-susceptible P. xylostella feeding on Bt leaves. In
contrast, C. plutellae developed to maturity in Bt-resistant P. xylostella fed on Bt oilseed rape
leaves, and there was no effect of Bt plants on percentage parasitism, time to emergence
from hosts, time to adult emergence, and adult emergence from cocoons (Schuler et al.,
2004). Parasitoids that had attacked Bt-resistant P. xylostella larvae on transgenic plants suffered
no measurable adverse effects of Bt toxins on the behavior of adults or on larval
survival. Continued ability of C. plutellae to locate and parasitize Bt-resistant P. xylostella on
transgenic crops might help to constrain the spread of genes for Bt resistance (Schuler
et al., 1999). Adult C. plutellae females are more attracted to Bt plants damaged by Bt-resistant
P. xylostella larvae than by susceptible hosts (Schuler et al., 2003). Mixtures of Bt and wildtype
plants demonstrated that the parasitoid is as effective in controlling Bt-resistant
P. xylostella larvae on Bt plants as on wild-type plants (Schuler et al., 2003).
Antagonistic Interactions
Bt Toxins
Egg parasitism of third-generation noctuids in Bt-transgenic cotton is lower than in the
conventional cottons (Wang and Xia, 1997). In transgenic cotton, abundance of the parasitoids,
C. chlorideae and Microplitis sp. decreased by 79.2% and 87.5%, and 88.9% and 90.7%,
respectively, in natural and integrated control plots (Cui and Xia, 1997, 1998). Ren et al. (2004)
observed that transgenic cotton (cry 1Ac and CpTi cotton, Zhongkang 310) suppressed the
growth and development of H. armigera parasitized by Microplitis mediator (Haliday) and
C. chlorideae or nonparasitized larvae. Cocoon formation and cocoon weight decreased
by 26.1% and 1 mg, respectively, while for C. chlorideae, the reductions were 17.9% and
5.1 mg, respectively. Under laboratory conditions, rearing of the parasitoid C. chlorideae on
H. armigera larvae fed on the Cry1Ac-intoxicated diet results in reduced cocoon formation
(Figure 11.5) (Sharma, Dhillon, and Arora, 2008). There is a signifi cant reduction in survival
of C. chlorideae reared on H. armigera larvae fed on Bt-transgenic cotton leaves (Figure
11.6). However, the reduced survival of the parasitoid is not due to the direct toxicity of Bt
to the parasitoid, but early mortality of the host larvae (Sharma, Pampapathy, and Arora,
2007). The larvae exhibited delayed development on transgenic cotton and, in some cases,
abnormal development was also observed. The total hemolymph protein content of the
larvae fed on transgenic cotton was lower than that on the nontransgenic cotton, which
might result in delayed and abnormal development of the parasitoid (Ren et al., 2004).
Decreased parasitism has been attributed to lower density and poor nutritional quality of
the bollworm, H. armigera larvae (Cui and Xia, 1999; Wu, Peng, and Jia, 2003). Parasitism
of H. virescens larvae by C. sonorensis was lower on Bt transgenic tobacco than on the
nontransgenic tobacco, and was lower for Bt-susceptible than the Bt-resistant larvae