All the field populations evaluated exhibited some degree of azinphos-methyl tolerance in relation to the laboratory susceptible strain. Biochemical results demonstrated that esterases are at least one of the principal mechanisms involved in tolerance to this insecticide.

The authors evaluated biomarker responses in caged larvae of the amphibian Rhinella arenarum in water channels during fruit production season and compared them with those elicited by a transient exposure to azinphos methyl (AzM) (0.02-2 mg/L; 4 h), the main pesticide applied in the Alto Valle region, Patagonia, Argentina, taking into account the maximum environmental concentration detected in superficial water (22.5 µg/L). The traditional biomarkers of organophosphate exposure, acetylcholinesterase (AChE) and carboxylesterase, were inhibited in tadpoles after one week of exposure in channels potentially receiving pesticide drift, whereas the antioxidant glutathione (GSH) and the detoxifying activity of GSH S-transferase (GST) were induced. In a two-week monitoring study, AChE activity was induced in larvae exposed at the agricultural site, and carboxylesterase showed an inhibition followed by return to control values, suggesting an exposure-recovery episode. Antioxidant glutathione levels were first depleted and then surpassed control levels, whereas GST activity was continuously induced. These responses were mimicked in the laboratory by 2 mg/L AzM-pulse exposure, which notably exceeds the expected environmental concentrations. The results draw attention to the complexity of responses after pesticide exposure, strongly depending on exposure time-concentration and recovery periods, among other possible factors, and support the necessity of the integrated use of biomarkers to assess exposure episodes in agricultural areas.

No abstract

The organophosphorous compound azinphosmethyl (AzMe) is applied extensively in northern Patagonia (southern Argentina) to manage codling moths (Cydia pomonella). This area is irrigated by fast-flowing channels that provide a favorable habitat for many species, including amphipods (Hyalella curvispina) and a field-mixed population of black flies (Simulium bonaerense, Simulium wolffhuegeli, and Simulium nigristrigatum). In the present study, AzMe susceptibility and carboxylesterase (CarbE) activity from both insecticide-exposed and nonexposed field populations were studied. The median lethal dose determined in codling moths from an insecticide-treated orchard was significantly higher (3.48 microg/insect) than that observed in those from an untreated orchard (0.69 microg/insect). Similarly, the median lethal concentration (LC50) determined in black flies collected from the treated area (0.021 mg/L) was significantly higher than that recorded in those from the untreated site (0.011 mg/L). For amphipods, both a subpopulation susceptible to AzMe (LC50, 1.83 microg/L) and a resistant one (LC50, 390 microg/L) were found in the treated area. Both subpopulations were more resistant to AzMe than the population from the untreated site (LC50, 0.43 microg/L). Significant differences (p < 0.001) in CarbE activities were observed between populations from pesticide-treated and untreated areas. Mean activities +/- standard deviation from treated and untreated sites were 0.21 +/- 0.16 and 0.016 +/- 0.008 micromol/min/mg protein, respectively, for codling moths; 2.17 +/- 1.71 and 0.81 +/- 0.35 micromol/min/mg protein, respectively, for black flies; and 0.27 +/- 0.10 and 0.14 +/- 0.07 micromol/min/mg protein, respectively, for amphipods. The results suggest that enhanced CarbE activity is one of the mechanisms that provide AzMe resistance in H. curvispina, Simulium spp., and C. pomonella populations from the insecticide-treated areas.

The Río Negro and Neuquén Valley is the most important apple and pear growing region in Argentina. Cydia pomonella L. (Lepidoptera: Tortricidae), the main fruit-tree pest is being controlled by azinphosmethyl (AzMe), acetamiprid (Acet), and thiacloprid (Thia) among other insecticides. The objective of this study was to evaluate the response of neonate larvae of codling moth to these three insecticides and on the role of cytochrome P450 monooxygenase in their toxicity. All field populations presented significantly lower mortality to a discriminating concentration (DC) of Acet and AzMe. In addition, 13 of the 14 populations showed significantly lower mortality to DC of Thia. Most of the field populations (71%) showed significantly higher 7-ethoxycoumarine O-deethylase activity compared with the laboratory-susceptible strain. While positive significant correlation (gamma = 0.59) was found between Thia and AzMe mortalities at the DC level, no significant correlations were detected between Acet and Thia (gamma = 0.35) or Acet and AzMe (gamma = 0.12). However, Acet and Thia mortalities were significantly correlated to the percentage of individuals exhibiting 7-ethoxy-coumarine O-deethylase activity activities higher than the mean upper 95% confidence limit of the susceptible strain (gamma = -0.52 and gamma = -0.63, respectively).