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Abstract:
The cotton bollworm, Helicoverpa armigera, is one of the major agricultural
pest species in the Old World and recently also of the New World. This
noctuid moth species is highly polyphagous and possesses a huge geographical
distribution and the ability to quickly evolve resistance to insecticides from different
chemical classes. There are different mechanisms known with which insects combat
insecticides. They are ranging from behavioral over morphological to physiological
adaptations. These resistance mechanisms can occur alone or in combination and
may change in the field according to changing selection pressures. A reduced
penetration through the cuticle of H. armigera larvae is known which reduces
the concentration at the target site. Also mutations of the target of pyrethroid
insecticides, organochlorines, and oxadiazines, voltage-dependent sodium channels,
were described that lead to high or lower resistance levels. Furthermore, both
carboxylesterases and cytochrome P450 monooxygenases were investigated to
determine their role in insecticide resistance. So far, only few enzymes were identified
in H. armigera which were proven to metabolize and thus detoxify insecticides.
Most studies deal with the resistance against pyrethroids. One important resistance
gene is the chimeric P450 CYP337B3 that is present in resistant and absent in
susceptible individuals. The corresponding enzyme is capable of metabolizing
fenvalerate and cypermethrin and thus confers resistance to H. armigera larvae. This
new resistance mechanism by recombination seems to play an important role in H. armigera populations throughout the world.
