Factors reducing the population density of the large poplar borer (Saperda carcharias L.).
The biology and ecology of Saperda carcharias (L.) were studied in poplar plantations in Bohemia and Moravia (Czechoslovakia) in 1958-68. Mortality was highest among the eggs and newly hatched larvae, the main cause being the healing over of the oviposition wounds in the trees; this resulted in these early stages becoming trapped. About 56% of the eggs and about 61% of the newly hatched larvae died in this way when the trees were growing vigorously, as compared with 35 and 34%, respectively, when the trees were growing less strongly. About 6.5% of the eggs were destroyed by Euderus caudatus Thoms., and about 5.5% of the larvae were attacked by parasites, mainly Ischnocerus rusticus (Geoffr.). In riverine forest, the great spotted woodpecker (Picoides major (Dendrocopos major)) destroyed about 10% of the larvae by pecking them out of their galleries, especially during hibernation. Some 13% of the larvae were destroyed by Pseudomonas septica, which was found in all areas. It was calculated from these findings that in healthy plantations in suitable agronomic areas where the trees were well cared for, 95% of the borers were unable to complete their development to the adult stage, as compared with an average of 70% when the trees were growing under adverse conditions. No evidence was obtained of varietal resistance to attack.