Laboratory Bioassays for Selecting Candidate Insecticides and Application Rates for Field Tests on the Western Spruce Budworm12

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Abstract
Derivation of a series of multiplication factors for suggesting field application rates of insecticides to control Choristoneura occidentalis Freeman based on laboratory data is described. The seven chemicals (acephate, carbaryl, fenitrothion, methomyl, permethrin, sulprofos, and thiodicarb) on which these factors are based had been field tested previously against C. occidentalis so that an estimated minimum effective dose to cause 90% mortality in the field (MED90) was available for each. The first laboratory bioassay estimated the effective dose resulting in 90% mortality (ED90) for each chemical by conventional procedures in which the doses tested resulted in 5 to 99% mortality when sprays were applied to larvae on foliage. In the second bioassay, each ED90 was reestimated by testing doses predicted from the first bioassay to result in 75 to 98% mortality. Finally, the rainfastness of each chemical applied at the ED90 dose was determined to assess the degree to which rainfall affects efficacy. The ratio of the MED90 to the precisely estimated ED90 for each insecticide was then determined. With future field tests of rainfast chemicals, conversion factors of 4, 8, and 12 seem appropriate. Increasing the factors to 5, 10, and 15 should suffice to assure comparable effects for chemicals adversely affected by rain.