Contents - Faperta

Transgenic Resistance to Insects: Interactions with Nontarget Organisms 349
less exposed to the transgene product as it is likely that not all of the prey will be contaminated.
Therefore, it is necessary to differentiate them from the host-specifi c parasitoids,
which are more likely to be affected by the toxins if the insect host acquires the toxins from
the plants.
Synergistic/Neutral Interactions
Bt Toxins
Predator levels in Bt cotton fi elds have been found to be signifi cantly greater than those
in conventional cotton fi elds where insecticides were used for controlling the bollworm,
H. armigera (Wu, Peng, and Jia, 2003). As the predator population increases, the outbreak
of cotton aphid, A. gossypii in mid-season is controlled effectively, while the mirids become
a major pest in Bt cotton because of reduced number of insecticide applications against
H. armigera. Campylomma diversicornis Reuter, a dominant predator on eggs and newly
hatched larvae of H. armigera, plays an important role in controlling insect pests in transgenic
Bt cotton fi elds (W.X. Liu et al., 2000).
No major differences have been observed in the abundance of generalist predators in
fi elds with transgenic and nontransgenic crops (Hoffmann et al., 1992; Flint et al., 1995;
Luttrell et al., 1995; Sims, 1995; Orr and Landis, 1997; Wang and Xia, 1997). Cui and Xia
(1999) did not observe a signifi cant increase in populations of predatory arthropods in the
Bt cotton fi eld, except that of Propylea japonica (Thun.). There was no apparent effect of
transgenic cotton on the relative abundance of predatory spiders, Clubiona sp. and Neoscona
sp., coccinellid, C. sexmaculatus, and the chrysopid, C. carnea. (Sharma, Pampapathy, and
Arora, 2007). In Bt transgenic maize, temporal abundance of nontarget arthropods (bug,
O. insidiosus; the syrphid, S. corollae; the ladybird, C. septempunctata; and the lacewing,
C. carnea) varied greatly over the season, but did not differ between Bt and non-Bt maize
(Bourguet et al., 2002). None of the coccinellids (three taxa), carnivorous carabids (three
taxa), and ants were affected by cry3A-transgenic potatoes resistant to the Colorado potato
beetle, L. decemlineata. Orius insidiosus was more abundant in transgenic fi elds than in nontransgenic
fi elds in one year, while spiders were abundant in another year. The predator
activity is not affected by pure transgenic and mixed seed potato crop (Riddick, Dively,
and Barbosa, 1998). However, signifi cant effects on predator numbers were observed
because of decline in the numbers of the insect hosts.
There are no adverse effects of Bt maize on pre-imaginal development or mortality of
C. carnea when reared on R. padi that had fed on Bt maize (Lozzia et al., 1998). Since there
is no Bt toxin in the phloem as established by Raps et al. (2001), the aphids fed to the predators
may have no Bt toxin, and thus no adverse effects of the transgenic plants could be
measured. Dutton et al. (2002) observed that C. carnea larvae were not affected when fed
spider mites, Tetranychus urticae Koch, that had been reared on Bt maize, even though the
spider mites were found to contain more Cry1Ab toxin as compared to the lepidopteran
larvae. Third instars of C. carnea showed a signifi cant preference for S. littoralis fed nontransgenic
maize. However, no preference was displayed when C. carnea had the choice
between R. padi fed on transgenic or nontransgenic maize. This lack of preference for
R. padi fed on either transgenic or nontransgenic maize has been ascribed to the absence
of the Bt protein in the phloem. In prey combinations with S. littoralis and R. padi, all three
larval stages of C. carnea showed a preference for R. padi regardless of whether they had
fed on transgenic or nontransgenic maize (Meier and Hilbeck, 2001). Romeis, Dutton, and
Bigler (2004) suggested that C. carnea larvae are not sensitive to Cry1Ab, and that earlier