Abstract
The effect of a number of plant extracts on the susceptibility of experimental insects to enthomopathogenic microorganisms has been studied. It is shown that the weight of the wax moth Galleria mellonella larvae tends to decrease by 30–50% under the treatments of polar and nonpolar extracts from the ledum sprouts and the reindeer lichen, while the crude hemlock extract had the opposite effect, contributing to the larva weight gain by approximately 30%. The treatment with the reindeer lichen extract causes synergistic effects on mortality from both the nuclear polyhedrosis virus and the fungal infection in the gypsy moth Lymantria dispar and the wax moth, respectively. It has been determined that the main components of this extract are perlatolic acid, usnic acid, and a third component whose exact chemical identity is still unknown. The usnic acid is the most prospective additive component to entomopathogenic microorganisms. The treatment with the usnic acid caused the increase in mortality from the entomopathogenic fungi Metarhizium robertsii and Beauveria bassiana in the Colorado potato beetle Leptinotarsa decemlineata and the wax moth. However, the maximum effect occurs only after the treatment with the crude extract, which can be explained by either the combined effects of all the extract components or the change in a range of the properties of the components in the presence of the other crude extract components.