Comparison of Chemical Effectiveness by the Multinomial Logit Technique

Abstract

The probabilities of four types of effects when three types of chemicals (pyrethroid, benzoylphenylurea [BPU], and juvenile hormone analogue [JHA]) were sprayed on fourth- or sixth-instar western spruce budworms (Choristoneura occidentalis Freeman) were compared with a multinomial logit model. Our results demonstrated that the BPU’s (triflumuron and diflubenzuron), the pyrethroids (fenvalerate and permethrin), and the JHA methoprene differed in effectiveness (death before pupation, successful pupation with no further development, emergence of an adult with major abnormalities or formation of an adult that did not fully eclose, or successful adult emergence) depending on the effect assessed, the concentration applied, and the developmental stage of western spruce budworms upon which the chemical was sprayed. Use of a scaling procedure permitted comparison of effectiveness patterns without the factor of chemical concentration. The patterns of the two BPU’s applied to fourth instars were the same, as were the patterns for the two pyrethroids. The patterns for the two pyrethroids applied to sixth instars were also the same. However, the patterns for the two BPU’s applied to sixth instars differed significantly. Uses of the multinomial logit model for investigations of chemical modes of action are described.