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.
Soleño
Jimena
J
Departamento de Química, Universidad Nacional del Comahue, Buenos Aires 1400, (8300) Neuquén, Argentina.
Anguiano
Liliana
L
de D'Angelo
Ana Pechen
AP
Cichón
Liliana
L
Fernández
Darío
D
Montagna
Cristina
C
D000818:Animals; D001118:Argentina; D001387:Azinphosmethyl / Q000494:pharmacology*; D004950:Esterases / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D007300:Insect Control; D019476:Insect Proteins / Q000378:metabolism; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects / Q000201:enzymology; D007928:Lethal Dose 50; D009036:Moths / Q000187:drug effects* / Q000201:enzymology*
D019476:Insect Proteins; D007306:Insecticides; D001387:Azinphosmethyl; D005982:Glutathione Transferase; D004950:Esterases