The average rate of diet uptake by the 1st–3rd instar nymphs of the pea aphid, Acyrthosiphon pisum (Harris), on chemically defined diets containing 0.0–5.0% amino acids varied from 0.08 to 0.23 μl/aphid/24 h and that by 4th instar nymphs to adults varied from 0.15 to 0.74 μl/aphid/24 h. The presence of amino acids increased the acceptability of diets to a great extent, as uptake on such diets was 2–5 times more than that on amino acid free diets. Uptake was lowest on diets lacking amino acids, and highest on those containing 3.5 and 2.5% amino acids by 1st–3rd instar nymphs and 4th instar nymphs to adults respectively. It is suggested that certain amino acids, either alone or in combination, act synergistically with sucrose as phagostimulants. Methionine was slightly phagostimulatory to the pea aphid and enhanced the acceptability of a free amino acid diet and of a sucrose solution.
As expected the rate of feeding increased as the aphids grew. Nymphs reached the adult stage, and reproduced on each diet, except on the one lacking amino acids. The longevity on different diets varied from 7 to 37 days. A concentration of 2–4% amino acids, with an optimum at 3.5%, appears to be essential for the growth, survival, and larviposition of the pea aphid.
Due to the punctures made in the stretched parafilm by aphids during feeding the rate of evaporation from fed sachets was significantly higher than that from unfed sachets. It is therefore suggested that in experiments where rates of feeding are measured by differential weighings of the sachets, these be renewed at 24-h intervals.