Autumn Populations of Green Peach Aphid on Peach Trees and the Role of Syrphid Flies in Their Control

To determine the trends in populations of the green peach aphid, Myzus persicae</it> (Sulzer), and the aphid forms present on peach trees in September and October before leaf fall, the arrival of 2 winged forms of the aphid and the buildup of the wingless female populations were investigated in the Yakima Valley, Washington, in 1965. In addition, the role that predaceous insects play in suppressing the aphid populations was observed. Results indicated that after the winged gynoparae arrived on the peach trees, the oviparous population rapidly increased and that male arrival was synchronized with maturing of oviparae. Syrphids were the only predators that effectively suppressed the aphids. Evidence of feeding activity by syrphid larvae was found on more than half the aphid-infested leaves. Maximum stimulus for egg deposition by syrphids was about 30–40 aphids per leaf.