Insecticide susceptibility of variegated cutworm 



JESO Volume 139, 2008 



Insecticide Assays 



Of the 4 insecticides commonly used for cutworm control, lambda-cyhalothrin 

 was most toxic to 3rd-4th instar VCW > permethrin > chlorpyrifos > methomyl. 

 Chlorantraniliprole was the most toxic of all the insecticides tested; spinosad and 

 metaflumizone were the least toxic (Table 1). In tests on the direct contact toxicity of 

 permethrin to different larval stages, at 0.001% solution, it was most toxic to 2nd instar 

 (25% average corrected for mortality) > 3rd-4th (17%) > 5th (0%) larvae. 



TABLE 1. Direct contact toxicity of 7 technical grade insecticides to 3rd-4th instar 

 variegated cutworm larvae from a southwestern Ontario strain established from field 

 populations collected in 2006. 



Insecticide 





Avg. corr. % mortality at % insecticide solution indicated 





0.0001 



0.001 



. 0.01 



0.1 



1.0 



Lambda-cyhalothrin 





97 



100 



100 



100 



Permethrin 







17 



100 



100 



100 



Chlorpyrifos 







2 



23 



100 



100 



Methomyl 











28 



79 



100 



Chlorantraniliprole 



15 



100 









Spinosad 







2 



14 



78 



100 



Metaflumizone 











3 



66 



84 



TABLE 2. Comparison of the direct contact toxicity of technical grade methomyl, 

 chlorpyrifos and permethrin to 3rd-4th instar variegated cutworm under identifical bioassay 

 conditions, 1977 and 2007. 



Insecticide 



Year 



Avg. 



corr. % mortality at % insecticide solution indicated 







0.001 



0.01 



0.1 





1.0 



Methomyl 



1977* 







70 



100 





100 





2007 







28 



79 





100 



Chlorpyrifos 



1977* 







72 



100 





100 





2007 



2 



23 



100 





100 



Permethrin 



1977* 



5 



100 



100 





100 





2007 



7 



100 



100 





100 



*Harris et al. 1977. Proc. Ent. Soc. Ont. 108: 63-68. 



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