FACTORS AFFECTING SPRAY DEPOSITION, DISTRIBUTION, COVERAGE, AND PERSISTENCE OF BIORATIONAL CONTROL AGENTS IN FOREST CANOPIES

In the past, population suppression of forest insects has been possible in Canada through the judicious use of quick-acting, broad-spectrum synthetic insecticides. Although beneficial, extensive use of these materials could potentially be hazardous to the environment. Currently, intensive research is being conducted to find alternatives with a relatively narrow spectrum of activity. This paper contains a brief overview of research carried out on four biorational insecticides (diflubenzuron, tebufenozide, azadirachtin and Bacillus thuringiensis), to study the role of formulation and delivery on field performance. At present, biorational control agents are being viewed as ''environmentally safe'' compared to conventional chemical pesticides. The data presented here indicate that diflubenzuron and tebufenozide persist in forestry substrates for many months, suggesting the need for a thorough risk-benefit analysis before establishing their ''environmental acceptability.'' In contrast, azadirachtin and Bacillus thuringiensis are too short-lived to be consistently effective, thus indicating the need to improve formulation and application methods. This paper also summarizes data for some of the several factors affecting field deposition, distribution, coverage and persistence of pesticides, viz., formulation ingredients and physical properties, application volumes, droplet spectra and droplets per unit area of targets, rain droplet sizes and ageing period of deposits, type of foliage, and nature of target surfaces.