Susceptibility of two strains of American serpentine leafminer (Liriomyza trifolii (Burgess)) to registered and reduced risk insecticides in Ontario.

Citation

Conroy, L., Scott-Dupree, C.D., Harris, C.R., Murphy, G., and Broadbent, A.B. (2008). "Susceptibility of two strains of American serpentine leafminer (Liriomyza trifolii (Burgess)) to registered and reduced risk insecticides in Ontario.", Journal of the Entomological Society of Ontario, 139, pp. 41-47.

Abstract

American serpentine leafminer, Liriomyza trifolii (Burgess), is a pest of floriculture greenhouses in Ontario. Growers rely on chemicals to provide acceptable pest control and, consequently, this leafminer has developed resistance to many insecticides. Our objectives were to determine if the American serpentine leafminer in Ontario has developed resistance to registered insecticides and to evaluate effectiveness of reduced risk insecticides with potential for inclusion in management programs. Two leafminer cultures were established - one collected from greenhouses in the Niagara region, the other being an insecticide susceptible strain never exposed to any of the test insecticides. Dosage-mortality curves were constructed using a leaf dip bioassay in which newly infested bean leaves were dipped in formulated insecticide solutions and larvae were allowed to develop until adults emerged. At the LC₅₀, the Ontario strain was resistant to abamectin (17.5x) and cyromazine (10.2x) and showed low levels of resistance to spinosad (2.8x) and chlorantraniliprole (3.0x) - such low resistance levels also could be due to natural variation in the strains. A comparison of LC₉₅ to application rates showed that the amount of insecticide required to kill 95% of the Ontario strain would be much higher than the recommended rate for cyromazine, just within the rate for abamectin, and lower that suggested rates for spinosad and chlorantraniliprole. While the LC₉₅s for spinosad and chlorantraniliprole were lower than suggested application rates. Nevertheless, the low level resistance shown by the Ontario strain suggests that these 2 insecticides may have the potential to develop higher levels of resistance over time.

Publication date

2008-12-31