Numerical Response of Coccinellids to Aphids in Corn in Southern Ontario

Populations of two abundant coccinellid species, Coleomegilla maculata lengi Timberlake and Hippodamia tredecimpunctata tibialis Say, responded rapidly to corn leaf aphid populations [Rhopalosiphum maidis (Fitch)] once the aphids became exposed to predation when the plants tasselled. Coleomegilla m. lengi oviposited at lower densities of aphids than did H. t. tibialis but H. t. tibialis was shown to have a greater numerical response than C. m. lengi at high densities of aphids due to its greater fecundity. The numerical response of the coccinellids by oviposition was linear with a lag of 1/2 week behind the aphid population.