Sequence and Regulatory Variation in Acetylcholinesterase Genes
Contribute to Insecticide Resistance in Different populations of
Leptinotarsa decemlineata
Abstract
Although insect herbivores are known to evolve resistance to
insecticides through multiple genetic mechanisms, resistance in
individual species has been assumed to follow the same mechanism. While
both mutations in the target site insensitivity and increased
amplification are known to contribute to insecticide resistance, little
is known about the degree to which geographic populations of the same
species differ at the target site in a response to insecticides. We
tested structural (e.g. mutation profiles) and regulatory (e.g. the gene
expression of Ldace1 and Ldace2, AChE activity)
differences between two populations (Vermont, USA and Belchow, Poland)
of the Colorado potato beetle, Leptinotarsa decemlineata in their
resistance to two commonly used groups of insecticides,
organophosphates, and carbamates. We established that Vermont beetles
were more resistant to azinphos-methyl and carbaryl insecticides
compared to Belchow beetles, despite a similar frequency of
resistance-associated alleles (i.e. S291G) in the Ldace2 gene. However,
the Vermont population had two additional amino acid replacements
(G192S, F402Y) in the Ldace1 gene, which were absent in the
Belchow population. Moreover, the Vermont population showed higher
expression of Ldace1 and was less sensitive to AChE inhibition by
azinphos methyl oxon than the Belchow population. Therefore, the two
populations have evolved different genetic mechanisms to adapt to
organophosphate and carbamate insecticides.