INFESTATION DYNAMICS OF DIORYCTRIA-SYLVESTRELLA (RATZ) (LEPIDOPTERA, PYRALIDAE) IN PRUNED MARITIME PINE (PINUS-PINASTER AIT)

The infestation dynamics of Dioryctria sylvestrella were studied for 2 consecutive years, in both pruned and unpruned maritime pine. In comparing four levels of pruning severity, the percentage of attacked trees and the location of attacks on the trunks were recorded. The level of attack of pruned trees strongly increased with the intensity of pruning, showing a significant positive correlation with the number of pruning wounds. The removal of dead branches did not result in any increase of infestation. The infestation of pruned trees had no contagious effect towards neighbouring unpruned trees. The location of attacks did not differ between either unpruned or any pruned tree treatments. The majority of the attacks were located in the vicinity of the branch insertion, and in 2-to 3-year-old internodes. In the second year, the percentage of pruned re-attacked trees continued to show a significant positive correlation with the severity of pruning. A model of infestation behaviour was hypothesised which involved two distinct phases. First, a primary attraction, mediated by components of oleoresin exuding from the pruning wounds, might allow the selection of an individual host tree. This attraction would be also quantitative and occur for at least 2 years. Second, female moths would select oviposition sites which would improve brood survival, providing easier access to suitable food resources.