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ARS Home » Research » Publications at this Location » Publication #166561
Title: SUSCEPTIBILITY OF LABORATORY AND FIELD STRAINS OF FOUR STORED PRODUCT INSECT SPECIES TO SPINOSAD

Author
item HUANG, FANGNENG - LOUISIANA STATE UNIV
item SUBRAMANYAM, B - KANSAS STATE UNIV
item Toews, Michael

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2004
Publication Date: 12/31/2004
Citation: Huang, F., Subramanyam, B., Toews, M.D. 2004. Susceptibility of laboratory and field strains of four stored product insect species to spinosad. Journal of Economic Entomology 97: 2154-2159.

Interpretive Summary: Insecticide resistance to currently used grain protectants has developed in stored-grain insect pests. Spinosad, a new reduced-risk insecticide derived from a bacterial fermentation product, will be labeled for application to stored grain in late 2004. There is a need to determine baseline susceptibility to spinosad as the first step in developing a resistance management plan. We tested this new insecticide against field and laboratory strains of common stored-grain insect pests. The field strains were generally 1.7 to 7.5 times less susceptible to spinosad poisoning than the corresponding laboratory strains. Both field and laboratory strains of the lesser grain borer were highly susceptible to spinosad. These results will be useful to help develop a resistance management program to prevent the development of insecticide resistance to spinosad in stored-grain insect pests.

Technical Abstract: Two field strains of the Indianmeal moth, Plodia interpunctella (Hübner); red flour beetle, Tribolium castaneum (Herbst); and lesser grain borer, Rhyzopertha dominica (F.), and one field strain of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), were collected from hard red winter wheat stored on farms in northeast Kansas. Fifty eggs of P. interpunctella and 25 beetle adults of each species were exposed to 100 g of untreated wheat or wheat treated with various rates of spinosad, to determine susceptibility of the field and corresponding insecticide-susceptible laboratory strains. Mortality of beetle adults and P. interpunctella larvae was assessed after 7 and 21 d post-infestation, respectively. Field strains of P. interpunctella, C. ferrugineus, and T. castaneum were less susceptible to spinosad than the corresponding laboratory strains. The LD50 and LD95 values for P. interpunctella and C. ferrugineus field strains were 1.7 to 2.5 times greater than values for corresponding laboratory strains. Adults of both laboratory and field strains of T. castaneum were tolerant to spinosad, resulting in <88% mortality at 8 mg/kg. The LD50 and LD95 values for the field strains of T. castaneum were 2.0 to 7.5 times greater when compared with similar values for the laboratory strain. The field and laboratory strains of R. dominica were highly susceptible to spinosad, and one of the field strains was relatively less susceptible to spinosad than the laboratory strain. Our results confirm a range of biological variability in field populations, which is consistent with findings for other compounds, and underscores the need to adopt resistance management programs with stored grain insect pests. The baseline data generated on the susceptibility of the four insect species to spinosad will be useful for monitoring resistance development and for setting field rates.