Resistance Mechanisms of Helicoverpa armigera

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.