The distribution and life-history of Milionia isodoxa Prout (Lepidoptera, Geometridae), a Pest of planted hoop pine in papua New Guinea

Abstract

Milionia isodoxa Prout is a serious defoliator of planted hoop pine, Araucaria cunninghamii, in the Highlands of Papua New Guinea. The insect has been found in seven mainland districts, and larvae have been collected from naturally occurring hoop pine in the Madang and Southern Highlands Districts. M. isodoxa is multivoltine, the life-cycle taking approximately eight weeks. The durations of the five larval instars are 4, 4, 4, 5 and 10 days, respectively, and of the pupal period approximately two weeks. The males feed primarily on organic solutes, the females on nectar, so that the sex ratio of adult M. isodoxa in the hoop pine plantations at Bulolo varies with the time of day and locality. Pupae may be attacked by two species of Ichneumonidae and one of Braconidae, and the ants Anoplolepis longipes (Jerd.) and Oecophylla smaragdina (F.) are particularly effective larval predators in the Bulolo plantations; some adults are killed by spiders. The fungus Beauveria bassiana is responsible for high pupal mortality in the Highlands. Frass-drop frequency studies of M. isodoxa larvae in the laboratory showed that feeding activity is greatest in the early instars, and is greater at night for all instars. Larvae reared at 21°C required 14 days more for development than did those reared under the normal daily fluctuation, 19–31°C.