Effects of Temperature and Light on Dispersal of the Pea Aphid, Acyrthosiphon pisum,1 and a Braconid Parasite, Aphidius pisivorus,2 in the Field3

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Abstract
Alate pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), and braconid parasites, Aphidius pisivorus C. F. Smith (Hymenoptera: Braconidae), were collected at 30-min intervals from 28 April to 17 May 1967 with Johnson-Taylor segregating suction traps placed level with the tops of alfalfa. Simultaneous records of air temperature and light intensity were taken at crop level. Data indicate the parasites were in flight 1 hr earlier in the morning and 21 min later in the evening than alate aphids. Temperatures below 0°C did not noticeably reduce populations of the pea aphid or parasite, but flight of both species was inhibited below about 6°C. The median temperature thresholds for parasite and aphid flight were 19.8 and 21.8°C, respectively. Parasites were in flight at lower light intensities in the morning and evening than alate aphids. The median light intensity thresholds for parasite and aphid flight were 2800 and 4300 foot-candles, respectively.

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