Role of CYP450 on the toxicity of azinphosmethyl and acetamiprid in pesticide-exposed and non-exposed field-populations of Simulium spp

CRISTINA MONTAGNA; LAURA B. PARRA MORALES; ENRIQUE ROSENBAUM

Santos, SP

Congreso; SETAC Latin America 12th Biennial Meeting; 2017

The resistance of insects to insecticides has become a dominant problem for contemporary agriculture. Most of resistant species are of agricultural importance, but many of them are insects of human health concern such as mosquitoes and flies. The Valley of Rio Negro and Neuquén produces a large proportion of Argentina?s apples and pears. This area is irrigated by fast-flowing channels providing a favorable habitat for many non-target species including blackflies (Simulium bonaerense, S. wolffhuegeli and S. nigristrigatum). Therefore, these species are highly exposed to pesticides through air drift from spraying, run-off of chemicals into irrigation channels and the discharge of pesticides by the cleanup of containers, sprayer tanks, and other devices. Previously, we have observed resistance to DDT and pyrethroids in blackflies from this area. The objectives of this study were to evaluate the toxicity of azinphosmethyl (AzMe) and acetamiprid (Acet) as well as cytochrome P450 activities in blackfly populations from pesticide-exposed (F. Oro) and non-exposed (P. del A) sites. Groups of 20 last instars were exposed for 24 h (15°C and a photoperiod of 16:8 h L:D) to different concentrations of each pesticide dissolved in acetone and applied as 0.1 mL in a final volume of 200 mL of filtered and dechlrorinated water. Mortality of both treated and control larvae were determined at the end of the exposure period.Resistance ratios were calculated as the LC50 F. Oro/LC50 P del A. CYP450 activity was individually assayed from both populations. Blackflies from F. Oro was as susceptible to AzMe (LC50 = 0.015 mg/L) as the ones from P del A (LC50 = 0,011 mg/L). On the other hand, the LC50 of Acet from F. Oro (0.0066 mg/L) was 2.5-fold higher than the one from P del A (0.0026 mg/L). The average CYP450 activity of the pesticide-exposed population of blackflies was significantly higher (p < 0.001) (65 pg 7-OHC/min/adult) than the non-exposed ones (36 pg 7-OHC/min/adult). The distribution of CYP450 activities from the pesticide-exposed population showed a shift toward higher activities (kurtosis 6.1; skewness 1.6). On the other hand, the frequency distribution of CYP450 activity in blackflies from the control site did not evidence a high departure from normality (kurtosis 0.46; skewness 0.39). Therefore, we conclude that the differences in toxicity to Acet between insecticide exposed and non-exposed populations of blackflies are at least due to enhanced CYP450 activity.