Susceptability of leafminers to insecticides 



JESO Volume 139, 2008 



SUSCEPTIBILITY OF TWO STRAINS OF AMERICAN 

 SERPENTINE LEAFMINER (LIRIOMYZA TRIFOLII (BURGESS)) 

 TO REGISTERED AND REDUCED RISK INSECTICIDES 



IN ONTARIO 



L. CONROY, C. D. SCOTT-DUPREE 1 , C. R. HARRIS, 

 G. MURPHY 2 , A. B. BROADBENT 3 

 Department of Environmental Biology, University of Guelph, 

 Guelph, Ontario, Canada, NIG 2W1 

 email: cscottdu@uoguelph.ca 



Abstract J. ent. Soc. Ont. 139: 41^7 



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 LC 5() , the Ontario strain was resistant to 

 abamectin ( 1 7.5x) and cyromazine ( 1 0.2x) and showed low levels of resistance 

 to spinosad (2.8x) and chlorantraniliprole (3. Ox) - such low resistance levels 

 also could be due to natural variation in the strains. A comparison of LC 95 

 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 LC 95 s 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. 



Published November 2008 



1 Author to whom all correspondence should be addressed. 



2 Ontario Ministry of Agriculture, Food and Rural Affairs, Vineland, ON, LOR 2E0 



3 SCPFRC, Agriculture and AgriFood Canada, London, ON, N5 V 4T3 



41 



