'aphidicidal' is formed from 'aphid' (from New Latin/Greek 'aphis', meaning 'plant louse') + the combining form '-cidal' (from Latin root related to 'caedere', 'to kill').

'aphidicidal' was coined in modern English by attaching the productive combining form '-cidal' (seen in words like 'insecticidal' and 'herbicidal') to 'aphid', producing an adjective meaning 'that which kills aphids'.

Initially and still, it has the literal meaning 'killing aphids'; the sense has remained primarily technical and specific to aphids.