Nantucket pine tip moth development and population dynamics: Influence of nitrogen fertilization and vegetation control

It is commonly believed that Nantucket pine tip moth (Rhyacionia frustrana [Comstock]) feeding damage on loblolly pine (Pinus taeda L.) increases in relation to the intensity of silvicultural practices. Some studies have produced contrary or inconclusive data regarding this issue. This study was designed to examine the relationships between tree growth rates and tip moth development by enhancing growth with nitrogen (N) fertilizer and herbicide applications. The four treatments were N fertilizer, herbicide, herbicide+fertilizer, and untreated control. These treatments were monitored for tip moth damage levels, tip moth pupal numbers per pine shoot, insect population dynamics, and tree growth. Pine growth was significantly greater in the herbicide treatments than in the other treatments. There was a significant increase in diameter related to the fertilizer treatments, but no differences in tree height or volume were detected. Pupal weight was significantly lower in the herbicide treatment in the second year. Tip moth population fluctuations were greater in the herbicide treated plots than in the untreated control, and there were significant linear relationships between these fluctuations in the treatments versus percent parasitism, pupal weight, and diameter growth. This study shows that tip moth populations are not necessarily increased or decreased by intensive management practices, but can be less stable due to these practices.