ISSN: 0041-3216

ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 70 Number 2
Research Papers
Tomato pinworm (Lepidoptera: Gelechiidae) resistance to fenvaleratefrom localities in Sinaloa, Mexicoand California, USA
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The cultivated tomato Lycopersicon esculentum Mill. is an important host of the tomato pinwonn Keiferia lycopersicella (Walsingham) (Lepidoptera: Gelechiidae) in Mexico and the southern United States of America. Because of reports of high fruit infestation in the Guasave and Del Fuerte valleys in Sinaloa, Mexico, despite frequent use of pyrethroid insecticides, resistance was suspected. A portable bioassay that assayed adult male susceptibility was used to determine the existence of resistance in this region. These data were compared with data collected in southern California where control was adequate. Comparison of adult male susceptibility with adult female and larval susceptibility indicated that male susceptibility was a good indicator of female and larval susceptibility. Using likelihood ratio tests to compare each field strain with a laboratory susceptible strain, all field strains were less susceptible to fenvalerate than the laboratory strain. Resistance ratios at the LC50 were greater than 3 in all cases and were as high as 2,141 at the LC90. Tomato pinworm collected in Sinaloa consistently showed lower susceptibility to fenvalerate than those collected in California which corresponded to the use of higher annual rates of pyrethroids in Sinaloa than in California. Tomato pinwonn resistance to fenvalerate in Sinaloa localities appeared to be extreme and should be a serious concern to management of this insect.
Keywords: Keiferia lycopersicella; Insecticide resistance; Fenvalerate; Tomato