Contents - Faperta

Deployment of Insect-Resistant Transgenic Crops for Pest Management 325
(NuCotn 33) acts additively in combination with polyhedrosis virus AcNPV-AaIT in reducing
bollworm damage (All and Treacy, 1997). Insects such as H. virescens, H. zea, T. ni, and
S. exigua are many times more sensitive to lamda cyhalothrin (Karate) sprays when they
have a prior exposure to Bt (Harris et al., 1998). Insecticides are highly effective for bollworm
control on transgenic cotton even at lower rates of application (Brickle et al., 1999).
Susceptibility of S. exigua to alpha-cypermethrin, methomyl, profenofos, and chlorfl uazuron
was 1- to 1.6-fold lower in larvae fed with Bt cotton than in larvae fed with common
cotton (Xue, Dong, and Zhang, 2002). However, the activities of acetylcholinesterase and
carboxylesterase were greater in the larvae fed with Bt cotton than those fed with common
cotton. The enhanced insecticidal activity enables a more practical resistance management
strategy for transgenic crops.
The Bt sweet corn hybrids appear to be ideal candidates for use in IPM programs for
both the fresh and processing sweet corn markets, and their use should drastically reduce
the quantity of insecticides currently used to control these pests in sweet corn. Firstgeneration
European corn borer, O. nubilalis damage was reduced or eliminated with the
use of the Bt hybrids (Archer et al., 2000). However, yield of Bt hybrids was 8% less than
standard hybrids when an insecticide was applied. The value of protection offered by Bt
maize is generally lower than the seed premiums (Hyde et al., 1999, 2001). Kernel damage
was reduced to 1.7 cm 2 with fi ve applications of methomyl compared to 172 and 50 cm 2 on
Silver Queen and Bonus cultivars, respectively (Lynch et al., 1999). Corn earworm and
European corn borer control in transgenic sweet corn has been found to be superior to
that achieved in nontransgenic varieties sprayed with insecticides (Doohan et al., 2002).
Damaged ears of transgenic varieties ranged from 0 to 6% and most damage was restricted
to the tip of the silk end. In contrast, 40% of nontransgenic varieties had damaged
ears, despite regular spraying of insecticides. Ears of nontransgenic varieties were damaged
more severely and many late-instar larvae were recovered. The percentage decrease
in insecticide use doubled from 13.2% in 1996 to 26.0% in 1998 (Pilcher et al., 2002), and
scouting for European corn borers decreased from 91 to 75%. After having planted
Bt maize and obtained excellent control of European corn borer, most farmers believed
that this insect had been causing more yield loss than previously suspected. In Germany,
grain yield of Bt-maize was approximately 14 to 15% higher than for untreated maize, and
insecticide and Bt treatments showed profi ts of 18 to 55, and 84 to 93 Euros ha 1 , respectively
(Degenhardt, Horstmann, and Mulleder, 2003).
Newleaf potato plants have been found to be highly effective in suppressing populations
of Colorado potato beetle, Leptinotarsa decemlineata (Say), and provided better control than
weekly sprays of a microbial Bt-based formulation containing Cry3Aa, biweekly applications
of permethrin, or early- and mid-season applications of systemic insecticides (phorate
and disulfoton) (Reed et al., 2001). Biweekly applications of permethrin signifi cantly reduced
the abundance of several major generalist predators, and resulted in signifi cant increases in
the abundance of green peach potato aphid, M. persicae, a vector of viral diseases. Transgenic
Bt potato, Bt-based microbial formulations, and systemic insecticides appeared to be compatible
for IPM in potato. In contrast, the broad-spectrum pyrethroid insecticide permethrin
was less compatible with the IPM programs. Thus, transgenic crops can be used in conjunction
with chemical control without any detrimental or antagonistic effects.
Transgenic Crops and Biological Control
Recombinant DNA technology has allowed development of plants that are well suited for
use along with biological control. Unfortunately, plant breeders have continued to attempt