Resistance to chlorpyriphos in the predatory mite Kampimodromus aberrans

Abstract

The predatory mite Kampimodromus aberrans (Oudemans) is a key biocontrol agent in vineyards in Italy and Southern Europe. Its susceptibility to common pesticides (e.g., organophosphates) has been considered an important factor in preventing successful biocontrol of phytophagous mites. Nevertheless, populations of K. aberrans apparently resistant to organophosphates (OPs) have been reported to occur in Northern Italian vineyards. The resistance of K. aberrans to fungicides (e.g., mancozeb) has been demonstrated in the laboratory in France, but little is known about the toxicity of insecticides towards K. aberrans. Of these pesticides, the OP chlorpyriphos is extensively used in viticulture to control lepidopterans and homopterans. The present study investigated the dose-response effect of chlorpyriphos in four K. aberrans strains characterized by different levels of exposure to OP insecticides in the past: from never to frequently exposed. Resistance to chlorpyriphos is demonstrated for populations collected from vineyards and apple orchards. Resistance factors exceeded 145,000× for the three strains collected in vineyards and orchard. LC(50) values for resistant strains were 1.85-6.83 times higher than the recommended field dose of chlorpyriphos for vineyards and orchards (525 mg a.i./l).

A single nucleotide polymorphism in the acetylcholinesterase gene of the predatory mite Kampimodromus aberrans (Acari: Phytoseiidae) is associated with chlorpyrifos resistance

“…A G119S substitution (AChE torpedo numbering) in the single copy AChE gene has been associated with moderate decreases in chlorpyrifos susceptibility between resistant and sensitive strains of T. urticae (resistance ratio at LD50, RR 50 = 31), and a greater resistance ratio in cases of F331W replacement (RR 50 > 400). The K. aberrans strain with the highest level of insensitivity to chlorpyrifos (PO strain) described by Tirello et al (2012) has a RR 50 = 539,602, and this ratio is even higher than that found in the T. urticae populations with the F331W AChE genotype.…”

“…This substitution in the mosquito paralogous AChE seems not to be neutral under the selective pressure produced by organophosphate and carbamate treatments (Weill et al, 2004a). Indeed, when additional two chlorpyrifos-susceptible and three chlorpyrifos-resistant unrelated strains of K. aberrans were identified using a discriminant dose of chlorpyrifos (Tirello et al, 2012), KaAChE genotyping revealed the presence of the G191S substitution only in the resistant strains in the homozygous condition. The silent nucleotide polymorphisms found in the KaAChE cDNA of the resistant strains might also suggest that different G119S mutation events occurred independently.…”

“…Indeed, resistant strains of this predatory mite have successfully been released in vineyards and apple orchards where pest control strategies included chlorpyrifos and many other pesticides (Duso et al, 2009Ahmad et al, 2013). The resistance to chlorpyrifos of these strains has been definitively demonstrated (Tirello et al, 2012), but the underlying molecular mechanisms remain poorly understood. An initial clue came from the chlorpyrifos-resistant strain of T. pyri that exhibited a lower level of AChE activity than the susceptible strain, suggesting that the reduced substrate affinity observed in the biochemical assay might be associated with a modified AChE (Fitzgerald and Solomon, 1999).…”

“…Information about OP susceptibility was available for only two strains; specifically, the LE strain is highly susceptible to this insecticide and the PO strain is resistant to chlorpyrifos (resistance ratio at LD50, RR 50 = 539,602) (Tirello et al, 2012).…”

“…Nevertheless a K. aberrans strain, detected in North Italian vineyards under conditions of integrated pest management strategies (IPM) (Posenato, 1994), was also successfully released in other vineyards and apple orchards following organic or IPM strategies (Duso et al, 2007(Duso et al, , 2009Ahmad et al, 2013). Recently, bioassay studies have confirmed significant levels of chlorpyrifos resistance in this strain (Tirello et al, 2012) but molecular markers associated with this insensitivity are still unknown.…”