Relationship between Physical Properties of Aerosol Formulation and Its Insecticidal Efficacy

A pesticide formulation should be designed rationally to maximize its pesticidal efficacy by thoroughly investigating the relationship among the formulation factors, the physical properties of the formulation and its pesticidal efficacy. By the rational design of the formulation, pesticides can be used efficiently to the purpose, and maximum efficacy can be obtained by using the smallest amount of pesticide. Standing on this concept, authors studied the influence of the physical properties of aerosol formulations on their insecticidal efficacy. The insecticidal efficacy of an aerosol formulation is thought to be influenced by the behavior of the spray-droplets in the air and by the permeability of the insecticide through the cuticle of the insect to reach the nervous system. Then, the spray-droplet size and the solvent used for the aerosol formulation are thought to be the two most important factors. The spray-droplet size was decisive to maintain the concentration of airborne spray-droplets; the smaller the spray-droplets, the longer the concentration maintained. However, there existed an optimum spray-droplet size to maximize the insecticidal efficacy, which was around 30μm. This result was explained by the effect of the balance of the catch efficiency of airborne spray-droplets by flying insects which was affected by the inertia of spray-droplets, and the maintenance of the concentration of airborne spray-droplets which was affected by their settling speed. Among the solvents used for the aerosol formulation, the most effective one for knockdown efficacy was tetradecane. This solvent was thought to facilitate the insecticide to penetrate into insect through the cuticle.