Seasonal flight activity, phenology and physiological status of the major establishment pests ofEucalyptus nitensplantations,Heteronyx dimidiataandH. crinitus(Coleoptera: Scarabaeidae: Melolonthinae)

Abstract

Heteronyx dimidiata and H. crinitus are significant pests of young Eucalyptus spp. plantations in Tasmania, but little is known about their biology. Adult beetles feeding on the leaves and developing leaf buds of young seedlings can severely affect their growth and form or even kill them. Yellow-vaned funnel traps were used to monitor the flight activity of Heteronyx in a commercial plantation over 3 years. Visual searches were also conducted to determine the incidence of inactive beetles in the soil underneath trees and the presence of active beetles on leaves. Over 12 000 H. dimidiata and 1300 H. crinitus were collected during the study. The pattern of trap captures was similar in both species with over 90% of beetles being caught in spring and low numbers being caught throughout summer and autumn. High numbers of H. dimidiata were found in the soil surrounding the roots of Eucalyptus nitens seedlings, but very few larvae were present, indicating that oviposition occurs outside these plantations. Trap data suggest that spring flight activity is principally due to the emergence of overwintering adult beetles and that newly eclosed beetles typically invade plantations during late summer/autumn. Spring trap captures were strongly male biased, suggesting a scramble mating system where males were more active as they competitively searched for females. Over 65% of the variation in H. dimidiata activity in spring was accounted for by levels of solar radiation and wind. Females mated up to three times and ovarian development usually commenced in spring. The incidence of food in the crop was highest during autumn/winter, but the presence of fat in the abdomen was similar throughout the year. The use of yellow-vaned funnel traps to monitor the flight activity of diurnally active Heteronyx species in commercial Eucalyptus spp. plantations is recommended.