Role of AChE in Colorado Potato Beetle (Leptinotarsa decemlineata Say) Resistance to Carbamates and Organophosphates

Abstract

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 in‐ hibit 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 organo‐ phosphate and carbamate insecticides, leading to modification of AChE (MACE). A range of other amino acid substitutions in AChE confer insecticide resistance, and these muta‐ tions typically reside near to or within the active site of the enzyme. Such AChE muta‐ tions, 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 carba‐ mates than to organophosphate insecticides. Pattern II resistance is characterized by re‐ sistance 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 insen‐ sitive 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.