In native forests in Australia, Mnesampela privata (Guenée) is uncommon, but in plantations, populations can outbreak. Two field trials (GES1 and GES2) were used to test whether oviposition on individual hosts by M. privata increases under plantation conditions of high host abundance. Oviposition on designated target trees was recorded over two consecutive seasons in arboreta where the relative abundance of preferred Eucalyptus hosts decreased, whereas the relative abundance of less preferred or noneucalypt trees increased. Neither trial supported the hypothesis that more eggs are laid on individual hosts when surrounded by trees of the same species. On the contrary, in the third arboretum type in GES2 (lowest relative abundance of eucalypts), more eggs were laid on target eucalypts whose immediate neighboring trees were noneucalypts. The average size of egg clutches increased between 1.3 and 11.7 times from the first to the second season of surveys, and the weight of females increased over the two consecutive seasons, which may have explained the increase in egg clutch size. It is proposed that outbreaks of M. privata occur in eucalypt plantations because high host abundance (and presumably also quality) drives the development of populations that are larger than can be supported by native forests.