Showing papers by "Canadian Forest Service published in 1984"

Effect of exposure time to bacillus thuringiensis on mortality and recovery of the spruce budworm (lepidoptera: tortricidae)

Abstract: Spruce budworm larvae were subjected to bioassay with Bacillus thuringiensis ( Bt ) to study the effects of exposure time and assay period on mortality, as well as on the possibility of recovery after a feeding-inhibitory dose. At all concentrations cumulative mortality increased until about day 10 of the assay. Extension of the exposure period from 1 day to continuous (equivalent to a 6 day exposure), resulted in a 500-fold reduction in LC50 (increase in potency) and an equivalent reduction in LT50. Some larvae recover if allowed to feed on diet without Bt even after exposure for 4 days to a very high concentration of Bt . The growth rate of recovered larvae is normal, but the time required for normal growth to resume varies with dose and exposure duration. Equations expressing the effect of exposure duration and dose on mortality and recovery period are presented. The implications of these findings for control of spruce budworm are discussed.

Joint action of a juvenile hormone analogue with benzoylphenylureas ingested by western spruce budworm, choristoneura occidentalis (lepidoptera: tortricidae)

Abstract: Mixtures of the juvenile hormone analogue (JHA) methoprene and each of three benzoylphenylureas (BPUs) were fed to sixth-instar western spruce budworm, Choristoneura occidentalis Freeman. The BPUs tested were diflubenzuron, BAY SIR 8514 ( N -[(trifluoromethoxy)phenyl]carbamoyl-2-chlorobenzamide), and EL-127063 ( N -[[[5-(4-bromphenyl)-6-metnyl-2-pyrazinyl]amino]carbonyl]-2-chlorobenzamide). Mixtures consisted of JHA:BPU combined in 1:9 proportions. Ingestion of methoprene combined with BAY SIR 8514 or diflubenzuron resulted in significantly lower mortality than expected under a simple model of uncorrelated, independent action. Ingestion of the mixture of methoprene and EL-127063, however, resulted in significantly enhanced toxicity over the upper response range (> 50% mortality).