AERIAL APPLICATION OF BACILLUS-THURINGIENSIS FOR SUPPRESSION OF GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) IN POPULUS-QUERCUS FORESTS

In 1990, Bacillus thuringiensis Berliner var. kurstaki was applied by aircraft at more than twice the standard rate to peak populations of s econd-instar gypsy moth, Lymantria dispar (L.), to see if woodlots cou ld be protected from defoliation even under intense pressure. Aqueous formulations of two products, Dipel 8AF (16.9 billion international un its [BIU]/liter, abbott Laboratories), and Foray 48B (12.7 BIU/liter, Novo Nordisk) were tested. Di[el was applied through both flat fan and rotary atomizer nozzles at 74 BIU/ha; Foray was applied through rotar y atomizer nozzles at 30 and 74 BIU/ha. Foray and Dipel applied at 74 BIU/ha provided similar levels of foliage protection (21.1 and 26.7% d efoliation, respectively) compared with control plots (80.9% defoliati on). Flat fan nozzles worked as well as rotary atomizer nozzles (27.9 and 27.9% defoliation, respectively). Under the conditions at our test sites where gypsy moth populations were peaking, B. thuringiensis app lied at 74 BIU/ha provided better foliage protection (21.1% defoliatio n) than when applied at 30 BIU/ha (46.3% defoliation). In 1991, standa rd rates (30 and 40 BIU/ha) of B. thuringiensis were tested in Crawfor d County, MI where there was a building infestation of gypsy moth. All B. thuringiensis treatments provided adequate foliage protection (17- 35% defoliation) compared with the control (73%). Populations were rap idly expanding in the 1991 test plot locations with little background mortality. Egg mass densities increased in control plots, whereas they remained nearly stationary in plots treated with B. thuringiensis. In 1991, however, gypsy moth populations had peaked in the test area. Eg g mass densities decreased slightly in control plots and in plots spra yed with B. thuringiensis. In our test blocks (which were typical of t he Michigan suppression program), changes in gypsy moth egg mass densi ties over one generation were more influenced by initial egg mass dens ity than by aerial application of B. thuringiensis.