Tomato moth, Tuta absoluta   (Meyrick) response to insecticides in Arica, Chile

Larval susceptibility of Tuta absoluta (Meyrick) collected on tomato (Lycopersicon esculentun Mill.) crops in Azapa, Arica (18° 31' S lat, 70° 11' W long), Chile, was compared by toxicological tests with several commonly used insecticide doses applied on two development stage larvae groups (stadia 1-2 and 3-4). To determine resistance to insecticides, LD50, LD90, and regression slopes between probit mortality and log dosage were calculated. Resistance to studied insecticides was verified, since LD50 at least doubled those in Ovalle and Quillota, locations where T. absoluta had the greatest resistance in other study. Deltamethrin and mevinphos were the least and most toxic compounds, respectively. Larvae of both development levels were equally susceptible to deltamethrin, while larger larvae were more resistant to mevinphos than smaller ones. Results with esfenvalerate and λ - cyhalothrin on large larvae, and metamidophos on small larvae, were too variable and this caused a defective probit analysis and resistance evaluation to these insecticides in such larval groups. Parasite may have also developed resistance to insecticides; this may explain the resurgence of populations in the Valley. Possible parasite resistance, which are present even with insecticide treatments at extremely high dosages, could have affected accuracy in the regressions obtained, particularly on large larvae