NATURAL MORTALITY OF THE PINE SHOOT MOTH, RHYACIONIA BUOLIANA (SCHIFF.) (LEPIDOPTERA: OLETHREUTIDAE), IN ENGLAND

Abstract

A population of R. buoliana infesting a young Scots pine plantation was followed through three generations. The most important causes of mortality in the population were an egg parasite, probably Trichogramma evanescens; the failure of the third instar larvae to establish themselves in the buds; two external parasites, Scambus sagax attacking the larvae in the autumn and Exeristes ruficollis attacking the larvae in the spring; three internal parasites, Orgilus obscurator, Temelucha interrupter, and Eulimneria rufifemur, attacking the larvae in the autumn but killing it in the spring after the trees were damaged; and a fungus, Paecilomyces farinosus, that usually killed the larvae in the autumn. The total proportion of the population killed by parasites and fungus was usually constant from one year to the next, though the abundance of T. interruptor increased.Most of the annual fluctuation in abundance of the moth was caused by the differential survival of the third instar larvae. After a cool summer the third instar larvae were not developed until September and most of them failed to establish themselves in the buds and perished. On the other hand in a warm summer when the larvae developed earlier and attacked the buds in July, most of them were successful.