The pine engraver beetles (~ spp.:Coleoptera:Scolytidae) may be serious pests depending on certain prerequisite conditions. In their secondary or "normal" role they breed in slash and damaged, dying, and dead trees. The broods emerging from these sources normally attack similar material. When such material is scarce due to cessation of cutting operations in mid-season or when conditions are especially favorable for brood development, an excess of beetles is often produced which, due to the lack of more suitable material, attack healthy trees. Repeated attacks cause these trees to succumb and die. When normally healthy trees are weakened by fire, flood, defoliation, drought, stagnation, etc., then they become more acceptable host material for successful engraver attacks. When the production of a very large number of beetles in "normal" breeding material coincides with physiological stress in "healthy" trees, then population explosions can occur. When large numbers of beetles and low host vigor do not coincide, spot kills cornnon1y occur. According to Thatcher (32), spot kills, although not conspicuous, add up to large volumes of timber loss each year. / Ph. D.

The significant results of this research were: 1) A laboratory colony of H. bajulus was established and information on the N. A. biotype was collected. At this time it is too early to make any significant statements of comparison between European and N. A. biotypes. However, preliminary results indicate that the mean number of eggs per female, and the size and longevity of N. A. adults appear different than European beetles; 2) Outdoor survival studies of the larvae indicate that H. bajulus can live under natural conditions in Virginia's varied climatic regions. Over the course of two years 27 adults have been collected in such field conditions as fence posts, outhouses, screen windows, building exteriors, and free flying in open fields. This information, along with survival studies, strongly suggest the presence of natural populations; 3) The environment in which H bajulus larvae are located greatly affects its chances of survival. Larvae in attics can survive the fluctuating environmental condition, but growth and development are prolonged and potential structural damage minimal. Under these conditions H. bajulus larvae are more likely to undergo natural mortality over several years. In optimum (stable) conditions H. bajulus will increase their feeding and development. Under these conditions infestations that are left unchecked may lead to serious structural damage and reinfestations. / Master of Science