Seasonal abundances of the mamane moth, its nuclear polyhedrosis virus, and its parasites

Abstract

The mamane moth (Uresephita polygonalis, Denis and Schiff.) is a serious pest of the mamane tree (Sophora chrysophylla, Salish.) on the island of Hawaii. The larvae of this moth feed on mamane leaflets sometimes causing serious defoliation. The life cycle and development of U. polygonalis were determined by observation of laboratory reared animals. Results of laboratory tests indicated that Acacia koa was not a host of the larvae. Seasonal abundance of the moth was estimated from monthly counts of eggs and larvae collected from four sampling sites. Apparently there are no positive correlations of population dynamics with rainfall, humidity, temperature and vegetative flushing of mamane. Four parasites were reared from U. polygonalis collected at the sampling site. Only one of these, an ichneumonid (Rorogenes blackburni, Cameron) appeared to be an important parasite, although it did not occur in high enough numbers to seriously affect mamane moth populations. The nuclear polyhedrosis virus, present only at sampling site 4, was a major factor in the regulation of the U. polygonalis population at that site. Laboratory tests indicated that larvae from all sites were highly susceptible to the virus. However, why the virus did not occur at all sites remains to be determined. Possibly the amount of sunlight and ultraviolet radiation reaching the trees and ground beneath them affects the virus which is inactivated by light. Thus, in years when U. polygonalis populations do not reach high levels, the virus is confined to cloud covered areas such as site 4. The virus disease plays a major role in population regulation when it reaches epizootic levels.