Flight activity of the damson–hop aphid, Phorodon humuli.

Flight activity of Phorodon humuli was monitored using suction traps, laboratory studies and mark and recapture experiments. Emigrants were trapped as they flew from a Myrobalan (Prunus cerasifera) hedge and among dwarf hops (Humulus lupulus). Daily flight curves were bimodal with 69% and 38% of emigrants caught in the morning peak near Myrobalan and among hops, respectively. The median period of flight activity was from 2 h after sunrise until 30 min before sunset. The lower temperature for flight was 13.5°C in the field and 14.9°C for take off in the laboratory. Variations in wind speed had little effect on flight activity explaining <2.5% of the total variance among insect counts. The percentage of emigrants on hop declined exponentially with time. The relationship, y= 10.9(±2.0) + 64.3(±2.3) × 0.92(±0.01)^t where t = daylight hours (standard error in parentheses), explained 98.3% of the variance. Hence, 62% of new arrivals flew within 1 day of arrival and 79% within 2 days. Similar numbers arrived as departed at 08:30, 10:30 and 12:30 h, but at 14:30 h twice as many arrived than departed and at 16:30 h, the accumulation was threefold. Daily flight curves of return migrants and males leaving hop were bimodal with 70% and 80%, respectively, trapped in the earlier peak. In the field, the median lower temperature for flight was 13.2°C for return migrants and a nonsignificantly different 12.8°C for males. The mean temperature for take off by return migrants was 15.7°C in the laboratory.