Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/28/2000
Publication Date: 2/10/2001
Citation: Knight, A.L., Dunley, J., Jansson, R.K. 2001. Baseline monitoring of codling moth (Lepidoptera: Tortricidae) larval response to benzoylhydrazine insecticides. Journal of Economic Entomology. 94:264-270. Interpretive Summary: A larval bioassay technique was developed to conduct field surveys of the response of codling moth populations to two new benzoylhydrazine insect growth regulator insecticides, tebufenozide and methoxyfenozide. The initial tests showed that the bioassay was improved by extending its length to 14 days and excluding insects in the last larval stage. In addition, we showed that our laboratory colony responded to both insecticides similarly to a field-collected population pooled from five certified-organic apple orchards and reared in the laboratory for one generation. Methoxyfenozide was approximately 10-fold more active than tebufenozide for codling moth larvae. The responses of 18 field-collected populations tested during 1998 and 1999 exhibited a five- and nine-fold range in responses to tebufenozide and methoxyfenozide, respectively. The responses of all but six field-collected populations differed from the laboratory strain. Five of these six populations were collected from orchards with no history of organophosphate insecticides. The response to methoxyfenozide of one field-collected population reared in the laboratory declined four-fold after three generations, but its' response was still significantly different from the laboratory population.
Technical Abstract: A larval bioassay was developed to measure the response of codling moth, Cydia pomonella (L.), to the benzoylhydrazine insect growth regulators, tebufenozide and methoxyfenozide. The bioassay was developed by testing larvae from a laboratory colony and a pooled field-collected population from five certified- organic orchards. No differences in larval responses were found between the two populations in either 6- or 14-d bioassays. LC50's were significantly lower in the 14-d than the 6-d bioassays for both populations. Age was a significant factor affecting larval mortality to both insecticides. Fifth instars were significantly less susceptible than other larval stages. The responses of 3rd and 4th instars were similar. LC50's to methoxyfenozide were approximately 10 times lower than with tebufenozide. LC50's among the 18 field-collected populations tested exhibited a five to nine-fold range in responses. The responses of all but six field-collected populations were significantly different from the laboratory strain. Five of these populations were collected from orchards with no history of organophosphate insecticides. The LC50 to methoxyfenozide of one field-collected population reared in the laboratory declined four-fold after three generations.