Contents - Faperta

Transgenic Resistance to Insects: Interactions with Nontarget Organisms 353
Synergistic/Neutral Interactions
Bt Toxins
Cotton bollworm parasitoid, Campoletis sonorensis (Cameron), and transgenic plants act
synergistically, decreasing the survival of H. virescens larvae beyond the level expected for
an additive interaction. Synergistic increases in mortality and parasitism have also been
detected when development rates on toxic plants and control plants were equal ( Johnson
and Gould, 1992). The parasitoid, Cardiochiles nigriceps (Viereck) does not reduce the survival
of H. virescens larvae signifi cantly, and its activity is not infl uenced by the transgenic
plants (Johnson, 1997; Johnson, Gould, and Kennedy, 1997). Riggin Bucci and Gould (1997)
reported that percentage parasitism, by the parasitoid of diamond back moths, Diadegma
insulare (Cresson) was not signifi cantly different between the mixed and nonmixed plots
of transgenic plants. There are no adverse effects of transgenic maize on parasitization
of the European corn borer, O. nubilalis by Eriborus tenebrans (Graven) and Macrocentrus
grandii (Goid.) (Orr and Landis, 1997). Similarly, Volkmar and Freier (2003) did not observe
any clear effect of Bt transgenic maize on the activity and abundance of parasitoids. The
parasitoids, Oedothorax apicatus (Black.) and Erigone atra (Black.) were dominant species in
all fi elds, while E. dentipalpis (Wider) was dominant at Halle. Meioneta rurestris (Koch.),
Porrhomma microphthalmum (Cambridge), and Pardosa agrestis (Westring) were dominant at
Oderbruch. Parasitism of H. armigera eggs has been found to be greater on transgenic Bt
cotton (probably because of healthy crop and more egg laying) than on the nontransgenic
one (Figure 11.4), but there were no differences in larval parasitism. However, parasitism
by the larval-pupal parasitoids was quite low on the transgenic cotton as very few larvae
survived long enough to ensure complete development of larval-pupal parasitoids.
Lectins
Transgenic sugarcane expressing GNA and ingested via Eoreuma loftini (Dyar) was not
acutely toxic to the parasitoid, Parallorhogas pyralophagus (Marsh) (Tomov and Bernal, 2003).
In the fi rst generation, adult longevity increased by two days; and cocoon to adult and egg
to adult developmental times were prolonged by one day in parasitoids exposed to
Parasitism on Helicoverpa armigera (%)
24
20
16
12
8
4
0
–4
Egg Larval Larval-pupal
Bt-transgenic Nontransgenic
FIGURE 11.4 Parasitization of Helicoverpa armigera eggs and larvae on transgenic and nontransgenic cottons
under fi eld conditions.