The effect of alcohol extract and essential oil from Juniperus sabina L. (Cupressaceae) on the survival and nutrition of the larvae Galleria mellonella L. (Pyralidae) has been studied. It is found that the essential oil has insecticidal, antifeedant, deterrent, and repellent properties. The loss of larvae with topical application of 0.2 μL of essential oil to the dorsal part (contact action) reaches 64.0%. Feeding larvae with food treated with essential oil J. sabina (200 μL of essential oil per 1.5 g of feed) is reduced 2.1 times compared to the control. It is shown that larvae G. mellonella avoid feeding on oil-treated feed for 14 days and actively move in the opposite direction from the treated feed when they are placed in Petri dishes. It has been established that vapors of essential oil suppress the development of larvae G. mellonella even when fed with untreated food—there is a lag in body weight and a delay in molting in the next age. The essential oil J. sabina also exhibits moderate toxicity (20.0%) when the larvae eat the treated food, i.e., possess intestinal action. The alcohol extract of J. sabina at a concentration of 2.5% of active substances (on dry residue) has a negligible effect on the loss of larvae in the case of treated feed (10.0% contact action). With topical application to the dorsal part, the extract causes 20.0% insect death. An alcohol extract of J. sabina does not elicit any antifeedant or repellent properties against larvae; however, a low level of deterrental activity, expressed in suppressing the formation and development of pupae of Galleria mellonella, is noted. Essential oil reduces the percentage of pupated larvae and emitted adults 3 times and the mass of larvae 40.7–48.0% when compared with the control.