Methomyl resistance

Resistance genes can be dominant, recessive, incompletely dominant, or incompletely recessive. Resistance to carbamates and organophosphates is usually dominant or incompletely dominant. Resistance to DDT, Bt, and spinosyns is usually recessive. Resistance to dieldrin is usually incompletely dominant. Resistance to pyrethroids is usually incompletely recessive. As shown in Figure 10.1 and 10.2, diamondback moth resistance to per-methrin was inherited as an incompletely recessive, autosomal factor, whereas resistance to methomyl was inherited as an incompletely dominant, autosomal factor. In cases of monofactorial inheritance of resistance to insecticides, the degree of dominance (D) in the progeny can be calculated, as described by Stone (1968), as follows ... 

Figure 10.2 Probit regression lines for methomyl against susceptible (S) and resistant (R) diamond back moths and their F, progeny. (From Yu, S.J., /. Econ. Entomol., 86, 680,1993. With permission.)...

Cross-resistance refers to a situation in which a strain that becomes resistant to one insecticide automatically develops resistance to other insecticides to which it has not been exposed. For example, selection of a strain of Spodoptera littoralis with fenvalerate resulted in a 33-fold increase in tolerance to fenvalerate. The resistant strain also showed resistance to other pyrethroids (11- to 36-fold) and DDT (lower than for the pyrethroids). Exposure of Cidex qninquefasciatus to fenitrothion resulted in the development of resistance to the carbamate insecticide propoxur. Similarly, selection of a housefly strain with permethrin resulted in a 600-fold increase in resistance to permethrin. The resistant strain also showed resistance to methomyl, DDT, dichlorvos, and naled (Hassall, 1990). 

Cotton is one of the crops most heavily reliant upon insecticide use. Although Bt cotton has been introduced in some areas, insecticide sprays remain as important components of cotton pest management programs. In some areas of the cotton belt, the majority of applications are made by aircraft. Issues which have been of regulatory concern in recent years include pest resistance associated with the frequent sprays, beneficial insect effects, worker exposure, and spray drift impacts on surfrice water quality. Products currently in use include organophosphates such as azinphos-methyl, methyl parathion, acephate, and disulfoton, pyrethroids such as lambda-cyhalodirin and carbamates such as methomyl. 

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