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Summary The browntail moth (Euproctis chrysorrhoea L.) fairly frequently completely defoliates oak trees in the part of the country South of the river Waal and in the “Achterhoek”, and buck thorn in the dunes region along the coast. In the “Veluwe” defoliation has been observed as an exception only. In the Northern provinces the species in question never caused important damage. In appears, therefore, that the North limit of the area in which outbreaks of the browntail moth occur, runs from West to East through the Netherlands. From time to time the limit moves to the North, and back again after a few years. An hypothesis was advanced according to which the increase of the damage and the movement of the limit of the outbreak region to the north would be caused by changes in the quality of the food, resulting from changes in weather conditions. In order to find out whether there is any likelihood of the nature of the food affecting the population dynamics of the brown tail moth in our country, two series of experiments were carried out. a. Field experiments with colonies placed in oak, hawthorn, apple and birch by the experimentor. It appeared that there were considerable differences in the development of the caterpillars on the different plant species and in the different localities. b. Laboratory experiments in which oak, hawthorn and apple leaves were fed to the caterpillars showed that they thrived best on hawthorn, less well on apple and least on oak. It is, therefore, concluded that an influence of the nature of the food on the population dynamics of the brown tail moth may be decisive. Further experiments are in progress.

The transmission of a nuclear polyhedrosis virus was investigated within a single generation of the Brown-tail moth, Euproctis chrysorrhoea (L.). Larvae infected with a lethal dose of virus were introduced onto bramble bushes naturally infested with the host, in separate studies in the spring and autumn. The course of infection was followed and clearly showed the development of a secondary infection peak in the spring. The presence of a secondary peak in the autumn was also suggested. These peaks are considered to have resulted from the passage of the virus from the primary infected larvae into further larvae. Virus dispersal was more widespread in the spring than in the autumn reflecting differences in larval dispersal. Zusammenfassung Uher das Auftreten sekundarer Infektionszahlen nach Anwendung eines Kernpolyeder-Virus gegen eine Population des Goldafters, Euproctis chrysorrhoea (L.) (Lep., Lymantriidae) Es wurde die Ubertragung eines nuklearen Polyeder-Virus in einer Generation des Goldafters, Euproctis chrysorrhoea (L.) untersucht. Die Raupen wurden mit einer letalen Dosis des Virus infiziert und dann in Brombeerstrauchern freigelassen, die naturlicherweise mit Goldafter-Raupen besetzt waren. Die Untersuchung wurde zweimal, im Fruhling und Herbst, durchgefuhrt. Der Verlauf der Infektion wurde verfolgt, und die Infektionskurve zeigte klar die Entwicklung einer sekundaren Spitze im Fruhjahr. Moglicherweise existierte auch noch eine sekundare Spitze im Herbst. Diese Spitzen stammen vermutlich aus einer Ubertragung des Virus von den primar infizierten Raupen auf weitere Raupen. Der Virus verbreitete sich im Fruhjahr weiter als im Herbst, vermutlich wegen unterschiedlicher Wanderlust der Raupen.