Larvae emerge in spring and can spread on their own or with the assistance of wind, birds, or mammals. In the nymph stage, the adelgid is immobile and settles on a single tree. Control methods Forest level The current leading biological control method of hemlock woolly adelgid is Sasajiscymnus tsugae, [originally called Pseudoscymnus tsugae]. S. tsugae is a black lady beetle that is relatively host-specific, feeding only on three known aldegid species, including HWA. This beetle was discovered in 1992 while feeding on hemlock woolly adelgid in its natural range of Japan. Since 1995, the Pennsylvania Department of Conservation and Natural Resources's Bureau of Forestry has released hundreds of thousands of adult S. tsugae beetles into affected hemlock forests of the eastern United States to determine its effectiveness at controlling the spread of the adelgid. From 1995 to 1997, experiments in Connecticut and Virginia found that releasing adult Sasajiscymnus tsugae beetles into infested hemlock stands resulted in a 47 to 88% reduction in adelgid densities within 5 months of introduction. The beetle's lifecycle is in parallel to the lifecycle of the hemlock woolly adelgid. Both lay eggs in the spring and hatching occurs nearly simultaneously. When hatched, S. tsugae larvae are highly mobile and feed on hemlock woolly adelgid eggs and larvae. Each S. tsugae larva can effectively consume about 500 adelgid eggs or nearly 100 developing adelgid nymphs. Laricobius nigrinus is another predatory beetle used as a biological control in response to hemlock woolly adelgid. Native to the western United States and Canada, L. nigrinus is known to prey exclusively on various woolly adelgids. L. nigrinus adults lay their eggs on top of wintering adelgid larvae in early spring, and upon hatching, the larval beetles feed on hemlock woolly adelgid. Also under study is Laricobius osakensis from Japan, a relative of L. nigrinus. They have shown promise in field trials. Individual trees The environmentally safest chemical control methods for treating individual trees are nontoxic insecticidal soap and horticultural oil. These are sprayed on the foliage and smother the insects as they dry. Most trees need to be treated on a yearly basis. Toxic systemic insecticides may be applied to the foliage and bark of a tree and can persist in killing the adelgid for up to four years after application. Caution must be used, and restraint exercised around bodies of water. Soil drenches/soil injections/bark sprays are used in larger