Observations on the flight periods of aphids in a Sitka spruce plantation in north-eastern Scotland.
The flight activity of aphids was recorded during 1969-71 in a plantation of Sitka spruce (Picea sitchensis) in north-eastern Scotland by means of sticky traps. Two flight periods occurred, in June-August and September-October. Fewer aphids were caught at 120 and 180 cm than at 60 cm above ground during June-August, while fewer were caught at 60 cm in September-October. After accounting for differences in wind speed at these heights, it was shown that aerial density was consistently higher at 60 cm. The first flight, which comprised mostly Elatobium abietinum (Wlk.), was three weeks early in 1971; this was associated with the rapid increase in aphid population on spruce shoots, due to the preceding mild winter. Reinfestation by this species after spraying could follow under similar circumstances. Sexuparae of Adelges laricis Vall. and A. viridis (Ratz.) were caught in the first flight, and gallicolae of A. cooleyi (Gill.) in the second; all galls on Sitka spruce were by gallicolae of A. cooleyi. Aphis fabae Scop. was the commonest species in the second flight.