Colorado potato beetle is one of the most important pests of potatoes and one of the most difficult insects to control. Over the years, none of the control techniques developed against this pest has provided long-term protection for potato crops. Worldwide, CPB is resistant to all major groups of insecticides, including organophosphates and carbamates. The target site of organophosphate (OP) and carbamate insecticides is the same; they inhibit the activity of AChE. The function of acetylcholinesterase (AChE) is degradation of acetylcholine (ACh - neurotransmitter) in the insect cholinergic synapses. Mutations in the AChE-encoding locus have been shown to confer target site insensitivity to organophosphate and carbamate insecticides, leading to modification of AChE (MACE). A range of other amino acid substitutions in AChE confer insecticide resistance, and these mutations typically reside near to or within the active site of the enzyme. Such AChE mutations, associated with insecticide resistance, mostly known as Ace in Drosophila, have also been observed in other species, including L. decemlineata. Based on bioassays and literature, modified/insensitive AChE confers two major patterns of resistance to OPs/carbamates. Pattern I resistance is characterized by significantly higher resistance ratios (RR) (much greater reduction in the sensitivity of AChE at the biochemical level) to carbamates than to organophosphate insecticides. Pattern II resistance is characterized by resistance ratios (and/or reductions in the sensitivity of AChE) that are approximately equivalent for both carbamates and OPs. There are also a few species for which an insensitive AChE has been reported and for which molecular data have been collected, but for which the resistance profiles for both OPs and carbamates have not been reported. For CPB, both patterns were registered.
Part of the book: Insecticides Resistance
Colorado potato beetle is one of the most important pests because of rapid and strongly developed resistance to insecticides. Resistant insects’ populations may detoxify or degrade the toxin faster than susceptible insects, or quickly rid their bodies of the toxic molecules. Resistant populations may possess higher levels or more efficient forms of these enzymes. Insecticide metabolic destruction inside the target organism is a common defensive mechanism, decreasing the duration and intensity of the exposure of the target site, lowering the probability of a lethal outcome. Three major mechanisms of metabolic transformation of insecticides underlie the vast majority of examples of biotransformation-based resistance: (i) oxidation; (ii) ester hydrolysis; and (iii) glutathione conjugation. Pyrethrins, pyrethroids, organophosphates, carbamates and other insecticides are degraded by hydrolysis. Insecticide detoxification primarily unfolds through molecule hydrolysis on different sites, thereby splitting ester, carboxyl-ester, amide and other chemical bonds. The most important hydrolytic enzymes are phosphoric triesters and carboxylesterases (ALiE esterases). Structural mutations in mutant carboxylesterases have now been widely described showing metabolic resistance to organophosphate and pyrethroid insecticides and relatively few cases of resistance to carbamates role. Carboxylesterases role in Colorado potato beetle resistance was confirmed by many authors.
Part of the book: Insect Physiology and Ecology