HUNGER, MOVEMENT, AND PREDATION OF COCCINELLA CALIFORNICA ON PEA APHIDS IN THE LABORATORY AND IN THE FIELD

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Abstract
Hunger and abundance of adult Coccinella californica (Mannerheirn) preying on pea aphids, Acyrthosiphon pisum (Harris), on alfalfa, Medicago sativa L., were assessed in the field. There was no consistent relationship between abundance or hunger and aphid density. The field beetles encountered in sampling were 4 times hungrier at each observed aphid density than expected from a simulation model of the predation that is driven by hunger. Laboratory studies revealed a circadian rhythm of beetle activity that was modified by hunger. An index of predatory potential (number of beetles times average hunger) was found to be a better indicator of impact of the beetles than absolute numbers of all coccinellids or hunger separately. It is suggested that the beetles encountered in simply walking through a field produce the most useful index of numbers of hungry beetles. This census must be done daily however because of the high vagility of adult coccinellids.