THE INFLUENCE OF NATURAL ENEMIES AND MIGRATION ON SPRING POPULATIONS OF THE GREEN SPRUCE APHID, ELATOBIUM-ABIETINUM WALKER (HOM, APHIDIDAE)

The importance of predators in the decline of the spring population of the green spruce aphid Elatobium abietinum was investigated. Natural enemies were slow in responding to changes in the numbers of the green spruce aphid and did not appear to be very effective. Although a vora cious predator both in the adult and the larval stage, the two spot la dy bird beetle Adalia bipunctata, the most common predator, failed to make an appreciable impact due to the slow numerical response. The pri mary factor that led to the crash in the population was the production of alate emigrants. Natural enemies do not seem to play an important role in the eventual reduction of the spring population of E. abietinu m. Host quality deterioration, which may or may not be accompanied by needle loss, was also an important factor in causing the aphid populat ion collapse, but should be considered as a secondary factor occurring in conjunction with the production of alatae due to changes in photop eriod.