The potency of two formulations of the nuclear polyhedrosis virus of the gypsy moth (LdMNPV) was evaluated in the laboratory. Both formulations were prepared with the same batch of LdMNPV produced in live insects by the USDA Forest Service. A Forest Service-recommended tank-mix preparation (LdMNPV, molasses, ultraviolet light screen, and sticker in water) was found to be about 20 times more potent than an experimental wettable powder preparation. The wettable powder also deterred feeding; the 20-fold difference in potency, though, is based on actual doses consumed. The addition of a stilbenedisulfonic acid derivative, Blankophor BBH, to the tank-mix and wettable powder preparations at a concentration of 1% (wt./vol.) reduced the LD50s by 42- and 214-fold, respectively. Blankophor BBH was also a moderate feeding deterrent to gypsy moth, Lymantria dispar (L.), larvae which could limit its efficacy as an enhancer of the virus. However, the addition of molasses to Blankophor BBH at least partially overcame the feeding deterrence. Other adjuvants were also tested for effects on larval feeding behavior, including Bond (sticker), Lignosite AN (ultraviolet light screen), and Carrier 244 (spray carrier). Of the materials tested, molasses was the strongest feeding stimulant, followed by Carrier 244. Bond and Lignosite AN had no detectable effect on feeding behavior in these tests. These data demonstrate the importance of monitoring potency during any formulation process, the possibility of enhancing the virus with adjuvants, and of understanding the effects of adjuvants on feeding behavior.