Cristina Mónica Montagna

Toxicological and biochemical response to azinphos-methyl in Cydia pomonella L. (Lepidoptera: Tortricidae) among orchards from the Argentinian Patagonia

BACKGROUND Azinphos-methyl is the main insecticide used to control codling moth on apple and pears in Northern Patagonia. The aim of this study was to evaluate the toxicological and biochemical response of diapausing larvae of codling moth in orchards subjected to different insecticide selection pressure. RESULTS Dose-mortality assays with azinphos-methyl in diapausing larvae of Cydia pomonella L. showed significant differences between the LD(95) from a population collected in one untreated orchard (2.52 microg moth(-1)) compared with that in a laboratory-susceptible population (0.33 microg moth(-1)). Toxicity to azinphos-methyl in field populations of diapausing larvae collected during 2003-2005 was evaluated by topical application of a discriminating dose (2.5 microg moth(-1)) that was obtained from larvae collected in the untreated orchard (field reference strain). Significantly lower mortality (37.71-84.21%) was observed in three out of eight field populations compared with that in the field reference strain. Most of the field populations showed higher esterase activity than that determined in both the laboratory susceptible and the field reference strains. Moreover, there was a high association between esterase activity and mortality (R(2)=0.64) among the field populations. On the other hand, a poor correlation was observed between glutathione S-transferase activity and mortality (R(2)=0.33) among larvae collected from different orchards. CONCLUSIONS 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.

Enhanced esterase activity and resistance to azinphosmethyl in target and nontarget organisms

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.

Comparative toxicity of parathion in early embryos and larvae of the toad, Bufo arenarum hensel

Received: 31 March 1993/Accepted: 24 October 1993 Parathion (O,O-diethyl O-p-nitrophenyl phosphorothioate) is a widely used agricultural insecticide highly toxic to mammals; however, very little is known about the detoxication capacity in some natural enemies of insects such as amphibians (Harriet al 1979; Llamas et al. 1985; Caballero de Castro et al 1991; Gauna et al. 1991). The biota may be stressed by discharges of pesticides, and it is therefore essential to know its potential effect on non-target organisms before irreversible change occurs. Some monitoring techniques use amphibian larvae as an useful indicator for aquatic contamination (Dumpert and Zeitz 1984; Beiswenger 1988; Williams et al. 1989). An ideal insecticide should be efficacious against pest species, but relatively safe for non-target organisms. To develop selective insecticides it is important to understand the differences and similarities of the defense systems between insects and the beneficial fauna such as predators and parasitoids. Thus, this report deals with a comparative study of parathion susceptibility on early embryonic and larval stages of the Argentinian toad

Risk assessment of Magnacide® H herbicide at Río Colorado irrigation channels (Argentina). tier 3: Studies on native species

We evaluated the potential environmental risk of the herbicide Magnacide (Baker Petrolite, TX, USA) using native species from Argentina, representing the ecosystem at the Irrigation Corporation (CORFO) channels at the Colorado River mouth, Buenos Aires, Argentina. Six species including fish, toads, snails, crustaceans, and insects were selected to perform studies on acute toxicity and repeated exposure effects. Magnacide H susceptibility ranking was Bufo arenarum (lethal concentration 50 [LC50] = 0.023 mg/L), Onchorhynchus mykiss (LC50 = 0.038 mg/L), Heleobia parchappii (LC50 = 0.21 mg/L), Hyalella curvispina (LC50 = 0.24 mg/L), Simulium spp. (LC50 = 0.60 mg/L), and Chironomus spp. (LC50 = 2.83 mg/L). The risk limit of 10th percentile (0.013 mg/L) determined by probit analysis on sensitivity distribution was similar to the one calculated from literature data. Risk assessment based on field application data suggested lethal exposures for more than 70 to 90% of the species up to 20 km downstream from the application point. Repeated exposures to Magnacide H of amphibian larvae at the lowest-observed-effect concentration caused some effects during the first exposure, but without cumulative effects. Amphipods were insensitive to repeated exposures, showing no cumulative effects. Whether short-term exposures may result in long-term sublethal effects on the organisms life history was not addressed by these laboratory tests. In conclusion, tier 3 studies indicate that Magnacide H application schedule is extremely toxic for most native species at CORFO-Rio Colorado channels, representing a high potential risk in the environment. The real environmental impact must be addressed by field studies at tier 4 giving more information on population effects and communities.

Evaluation of Cytochrome P450 Activity in Field Populations of Cydia pomonella (Lepidoptera: Tortricidae) Resistant to Azinphosmethyl, Acetamiprid, and Thiacloprid

ABSTRACT The Rio 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 (r = 0.59) was found between Thia and AzMe mortalities at the DC level, no significant correlations were detected between Acet and Thia (r = 0.35) or Acet and AzMe (r = 0.12). However, Acet and Thia mortalities were significantly correlated to the percentage of individuals exhibiting 7-ethoxycoumarine O-deethylase activity activities higher than the mean upper 95% confidence limit of the susceptible strain (r = -0.52 and r = -0.63, respectively).

Geographic variability in response to azinphos-methyl in field-collected populations of Cydia pomonella (Lepidoptera: Tortricidae) from Argentina

BACKGROUND Resistance to insecticides has been related to application history, genetic factors of the pest and the dynamic within the treated area. The aim of this study was to assess the geographic variation in azinphos-methyl response and the role of esterase and cytochrome P450 monooxygenase enzymes in codling moth populations collected within different areas of the Río Negro and Neuquén Valley, Argentina. RESULTS Diapausing field-collected populations showed resistance ratios at the LC(50) that were 0.7-8.7 times higher than that of the susceptible strain. Mean esterase (EST) and cytochrome P450 monooxygenase activities (expressed as α-N min(-1) mg(-1) prot(-1) and pg 7-OHC insect(-1) min(-1) respectively) were significantly correlated with LD(50) values from the field-collected populations. In addition, azinphos-methyl response was associated with the geographic area where the insect population was collected: populations from isolated and more recent productive areas presented significantly lower resistance ratios in comparison with populations from older and more intensive productive areas. CONCLUSION The populations assayed presented different resistance levels to azinphos-methyl. The response was highly correlated with the orchards geographic location. EST and ECOD activities were involved in azinphos-methyl response in the given region.

Mechanisms of resistance to DDT and pyrethroids in Patagonian populations of Simulium blackflies.

Mixed populations of the pest blackflies Simulium bonaerense Coscarón & Wygodzinsky, S. wolffhuegeli (Enderlein) and S. nigristrigatum Wygodzinsky & Coscarón (Diptera: Simuliidae) are highly resistant to DDT and pyrethroids in the Neuquén Valley, a fruit‐growing area of northern Patagonia, Argentina. As these insecticides have not been used for blackfly control, resistance is attributed to exposure to agricultural insecticides. Pre‐treatment with the synergist piperonyl butoxide (PBO) reduced both DDT and fenvalerate resistance, indicating that resistance was partly due to monooxygenase inhibition. Pre‐treatment with the synergist tribufos to inhibit esterases slightly increased fenvalerate toxicity in the resistant population. Even so, biochemical studies indicated almost three‐fold higher esterase activity in the resistant population, compared to the susceptible. Starch gel electrophoresis confirmed higher frequency and staining intensity of esterase electromorphs in the resistant population. Incomplete synergism against metabolic resistance indicates additional involvement of a non‐metabolic resistance mechanism, such as target site insensitivity, assumed to be kdr‐like in this case. Glutathione S‐transferase activities were low and inconsistent, indicating no role in Simulium resistance. Knowing these spectra of insecticide activity and resistance mechanisms facilitates the choice of more effective products for Simulium control and permits better coordination with agrochemical operations.

Evolution of insecticide resistance in non-target black flies (Diptera: Simuliidae) from Argentina

Black flies, a non-target species of the insecticides used in fruit production, represent a severe medical and veterinary problem. Large increases in the level of resistance to the pyrethroids fenvalerate (more than 355-fold) and deltamethrin (162-fold) and a small increase in resistance to the organophosphate azinphos methyl (2-fold) were observed between 1996-2008 in black fly larvae under insecticide pressure. Eventually, no change or a slight variation in insecticide resistance was followed by a subsequent increase in resistance. The evolution of pesticide resistance in a field population is a complex and stepwise process that is influenced by several factors, the most significant of which is the insecticide selection pressure, such as the dose and frequency of application. The variation in insecticide susceptibility within a black fly population in the productive area may be related to changes in fruit-pest control. The frequency of individuals with esterase activities higher than the maximum value determined in the susceptible population increased consistently over the sampling period. However, the insecticide resistance was not attributed to glutathione S-transferase activity. In conclusion, esterase activity in black flies from the productive area is one mechanism underlying the high levels of resistance to pyrethroids, which have been recently used infrequently. These enzymes may be reselected by currently used pesticides and enhance the resistance to these insecticides.

Environmental effect assessment of Magnacide H herbicide at Río Colorado irrigation channels (Argentina). Tier 4: in situ survey on benthic invertebrates.

The objective of this study was to assess the effects of Magnacide H (Baker Petrolite, TX, USA) usage on the aquatic ecosystem at the Cooperativa de Riego y Fomento (CORFO)-Rio Colorado irrigation channels, analyzing the effects on benthic invertebrates. At recommended treatment concentrations, Magnacide H kills most of the aquatic organisms; however, its presence in the channels is transient. Magnacide H caused a significant reduction in the number of taxa (58%), abundance (57%), and community diversity (67%) in the benthic assemblage with respect to untreated channels during the application period in the first year of the study. The herbicide reduced the abundance of the most abundant taxa: oligochaetes, chironomids, ostracods, and the snails Biomphalaria peregrina and Heleobia parchappii. In contrast, the herbicide only reduced invertebrate diversity during the application period at the second year of study. Two months after the applications had ceased, the benthic community in treated channels recovered their biotic attributes, reaching values similar to controls. Recovery could have occurred from upstream unimpaired reaches supplying migrating invertebrates that recolonized affected areas. Since recovery occurred within a reasonable period of time, we conclude that the impact of Magnacide H at CORFO-Río Colorado channels is acceptable from a regulatory point of view in the present practice protocol. Nevertheless, a strict control on the application conditions must be ensured to minimize the risk on the ecological receptors. We emphasize the recommendation that water release outside the channels is prevented until the product has dissipated.

Chemical characterization and toxicity of water-accommodated fraction of oil on the South American native species Hyalella curvispina

Chemical and toxicological crude oil analysis was performed on water-accommodated fraction of oil (WAF). This study characterized the chemical composition of WAF and its dissipation over a period of 192 h. Acute (96 h) and chronic (14 d) toxicity of WAF were evaluated on Hyalella curvispina from both reference (Los Barreales lake, LB) and hydrocarbon-contaminated (Durán stream, DS) sites. The total hydrocarbon (TPHs) concentration in WAF was 2.18 mg L-1. The dissipation rates of hydrocarbons in WAF showed a first-order kinetics, with half-lives ranging between 65 h-200 h. Amphipods from LB showed acute and chronic LC50 values of 0.33 and 0.018 mg L-1, respectively. Amphipods from DS exposed to pure WAF showed no mortality in either acute or chronic assays. Further biochemical and molecular research is required to determine the mechanisms underlying the resistance to WAF exposure on DS amphipods.