none Single and double aerial application treatments at 30 billion international units (BIU)/ha of an aqueous formulation (SAN 415 SC 32LV) of the NRD-12 strain of Bacillus thuringiensis Berliner were evaluated against a moderately dense population of gypsy moth, Lymantria dispar L. Egg mass densities before spray averaged 5,055 egg masses per ha; egg mass density after spray increased to over 19,500 egg masses per ha in the control woodlots but decreased to 2,600 and 4,500 egg masses per ha in the single and double application treatments. No significant defoliation occurred in the woodlots treated with NRD-12, but control woodlots suffered a significant (33%) defoliation. Reproduction; Reproductive productivity; Life cycle and development; Life cycle; Developmental stages; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Host parasite relationships; Diseases and disorders; Diseases; Microbial diseases; Land and freshwater zones; Nearctic region; North America; USA Lymantria dispar (Lymantriidae); Egg number; Bacterial toxin relations; Hatching success; Bacterial toxin & hymenopteran parasite relations; Larva; Development duration, bacterial toxin & parasite prevalence relations; Hymenopteran parasites; Cotesia melanoscelus, bacterial toxin effect on development relations; Prevalence; Cotesia (Hymenoptera) parasite, development duration relations; USA; Bacterial diseases; Bacillus thuringiensis; Reproductive success, development & parasite prevalence interrelations; Maryland; Caroline & Queen Anne Counties; Bacterial toxin effect on reproduction, development & parasite prevalence Cotesia melanoscelus (Braconidae); Lepidopteran hosts; Lymantria dispar; Prevalence; Lymantria dispar (Lepidoptera) host; Maryland; Caroline & Queen Anne Counties; Prevalence in lepidopteran host, influencing factors