Abstract
BackgroundOrganophosphate and carbamate insecticides irreversibly inhibit acetylcholinesterase causing death of insects. Resistance-modified acetylcholinesterases(AChEs) have been described in many insect species and sequencing of their genes allowed several point mutations to be described. However, their relative frequency and their cartography had not yet been addressed.ResultsTo analyze the most frequent mutations providing insecticide resistance in Drosophila melanogaster acetylcholinesterase, the Ace gene was cloned and sequenced in several strains harvested from different parts of the world. Sequence comparison revealed four widespread mutations, I161V, G265A, F330Y and G368A. We confirm here that mutations are found either isolated or in combination in the same protein and we show that most natural populations are heterogeneous, composed of a mixture of different alleles. In vitro expression of mutated proteins showed that combining mutations in the same protein has two consequences: it increases resistance level and provides a wide spectrum of resistance.ConclusionThe presence of several alleles in natural populations, offering various resistance to carbamate and organophosphate compounds will complicate the establishment of resistance management programs.
Highlights
Organophosphate and carbamate insecticides irreversibly inhibit acetylcholinesterase causing death of insects
Most mutations were identical in several species, suggesting that a low number of mutations can provide resistance. These findings presented a striking contrast to experiments of in vitro expression of mutagenesized AChE, which revealed that insecticide resistance should have genetic diversity [10]
Point mutations detected in D. melanogaster populations To identify mutations involved in insecticide resistance, the Ace gene encoding AChE in 30 strains of D. melanogaster harvested throughout the world was sequenced
Summary
Organophosphate and carbamate insecticides irreversibly inhibit acetylcholinesterase causing death of insects. Resistance-modified acetylcholinesterases(AChEs) have been described in many insect species and sequencing of their genes allowed several point mutations to be described. Their relative frequency and their cartography had not yet been addressed. Irreversible inhibitors have been developed as insecticides: organophosphates and carbamates. They have similar properties to acetylcholine but are hemisubstrates because they phosphorylate or carbamoylate the active-site serine leading to irreversible inhibition of the enzyme. This inhibition leads to an accumulation of acetylcholine in the synapses which in turn leaves the acetylcholine receptors permanently open, resulting in the death of the insect [1].
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