THE WINTER MOTH, OPEROPHTERA-BRUMATA L (LEP, GEOMETRIDAE), ON APPLE AND CHERRY - SPATIAL AND TEMPORAL ASPECTS OF RECOLONIZATION IN AUTUMN

The behaviour of adult winter moths Operophtera brumata (L.) (Lep., Geometridae) was investigated during the period of recolonization of fruit orchards in late autumn. Experiments were run simultaneously on both apple and cherry trees in order to detect differences and similarities on these two host plants. The study aimed at a better understanding of spatial and temporal aspects of recolonization of host plants and hence an improvement of monitoring methods. 1. Male flight and female migration coincide well enough to guarantee reproductive success. Recolonization of apple and cherry trees occurs simultaneously, but is delayed with decreasing altitude. 2. Male flight activity starts at sunset and reaches its maximum 2 h later. During the night activity decreases gradually to a minimum at sunrise. 3. Females approach tree trunks covering more than 3 degrees of the horizon. The dark part of the horizon appears to be the preferred crawling direction. The travelling time ranges from 1-10 days. 4. Within the tree crown the crawling paths of females are different on cherry and on apple. However, females preferably seek the top segment for oviposition an both cherry and apple trees. 5. On both cherry and apple significantly higher egg densities are found in the top part of the tree crown than in the lower parts. Older wood appears to be more attractive for oviposition probably due to better hiding places. Females seem to optimize between protection and access to food resources for their progeny. The implications of the results for winter moth monitoring in Swiss fruit orchards are discussed.