Acyrthosiphon pisum

Pea Aphid Acyrthosiphon pisum

This lone alate was swept from some Lucerne beside a footpath. My usual first line of attack with identifying aphids taken from a known plant is to look at the Influential Points website and identify what species of British aphid occur on that foodplant, and check the pages on that website for each one, eliminating any that are obviously different. That approach narrowed it down to two candidates: Pea Aphid Acyrthosiphon pisum and Blue Alfafa Aphid Acyrthosiphon kondoi. The colour of the antennae seemed better for pisum but the text suggested this may be unreliable, and the photos of pisum were more uniformly green insects lacking the paler yellower foreparts that mine showed. On kondoi there is a change in colour as the foreparts are darker brown, but that didn't really fit my one's paler yellow foreparts. I was also concerned that as I'd just swept a single insect, it was plausible that it had landed on the Lucerne by accident and was not really associated with Lucerne as a foodplant at all.

So to increase my confidence I turned to Blackman and attempted to key it. There were a few points where I wasn't entirely convinced I could see the details required in the key, for example I'm never confident counting the number of secondary rhinaria or whether I'm seeing all the hairs on the cauda/rostrum etc., however taking both leads when I wasn't sure I eventually ended up with pisum being the only satisfactory conclusion.

Pea Aphid Acyrthosiphon pisum showing rostrum RIV+V (with measurement and from both sides), cauda (without and with measurement), siphunculus (with measurement), antennae segment IV (with measurement of base) and body (with measurement), Wendling Beck Environment Project (Norfolk, UK), 9th June 2025

I had previously identified this species once, swept from Broom. I don't recall if I keyed this one out or if I was satisfied about the ID from its plant association and general appearance.