Prospección de la resistencia insecticida al dimetoato en la mosca del olivo "Bactrocera oleae" Gmelin (Diptera: Tephritidae) en Extremadura

TORRES-VILA L. M., J. PEREZ DE SANDE, 2002. Prospeccion de la resistencia insecticida al dimetoato en la mosca del olivo Bactrocera oleae Gmelin (Diptera: Tephritidae) en Extremadura. Bol. San. Veg. Plagas, 28: 281-286. The olive fruit fly, Bactrocera oleae Gmelin (Diptera: Tephritidae), is the most damaging pest in olive groves in Extremadura (Spain). Insecticide control, included or not in IPM programmes, is currently the only effective method to keep the populations at a level compatible with yield profitability. Since dimethoate is the insecticide traditionally used for chemical control, both in terrestrial and air sprayings, the current state of insecticide resistance in the olive fruit fly to that organophosphorous chemical was investigated during a four-year period (1998-2001) in Extremadura (Spain). Toxicological bioassays were completed in the laboratory by topical application on field-derived adults (<2-day-old) from 24 populations collected in larval stage. Dosemortality regressions, LD50's and their fiducial limits were estimated by probit analysis. Resistance factors (RF) were estimated at the LD50 level as RF = LD50 field population / LD50 susceptible population. RF's evidenced tolerance or very low resistance (RF = 2-4) in 87.5% of the populations, while in the remainder ones only low resistance (RF = 5-7) was recorded. Adult age (2 to 20-day-old) had not significant effect on mortality caused by dimethoate. The results suggest that the level of resistance of the olive fruit fly to dimethoate, although it could be incipient, does not seem to be currently alarming in Extremadura.