Three populations of the leafminer, Liriomyza trifolii (Burgess), were collected from commercial ornamental production greenhouses in the United States – two from California and one from Georgia – for susceptibility tests with the insecticides cyromazine (Citation), abamectin (Avid) and spinosad (Conserve). A leaf dip bioassay of leaves containing young (1-2 d old) larvae was used. Based on larval mortality, the three strains varied in both spectrum and level of resistance. CA-1, collected from Gerbera daisy, was moderately resistant to cyromazine (18-fold) and abamectin (22.5-fold) but highly resistant to spinosad (>188-fold). CA-2, collected from chrysanthemums, was not resistant to abamectin, had a low level of resistance to cyromazine (8.2-fold) but was extremely resistant to spinosad (1192-fold). GA-1, collected from chrysanthemums, had very low levels of resistance to cyromazine (5.5-fold) and spinosad (4.5-fold) but was moderately resistant to abamectin (30.3-fold). When reared in the absence of insecticide selection pressure, all three strains reverted to approximately the level of the reference strain. The CA-1 strain reverted in 9 generations to cyromazine and spinosad, however, the lowest level of abamectin resistance reverted to was 3.2-fold at F8. The CA-2 strain reverted in 5 generations to cyromazine and 4 generations to spinosad. GA-1 reverted in 5 generations to abamectin. Based on the results, it appears that resistance to these three insecticides is unstable, at least in the initial instance. Additionally, there was no cross-resistance among these three insecticides.
Species 1: Diptera Agromyzidae Liriomyza trifolii
Keywords: insecticide resistance, leafminers
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