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Literature Cited
Chapter 2
Acyrthosiphon pisum (Harris), Pea Aphid
(Homoptera: Aphididae)
B.D. FRAZER
Coccinella undecimpunctata L. was first encountered in pea aphid, Acyrthosiphon
piswn (Harris), infested alfalfa in May 1972. Since then it is routinely found on low-growing,
aphid infested plants including cereals, strawberries, and vegetables in numbers
about equal to the predominant native species, C. californica and C. trifasciata. C.
undecimpunctata is one of the first coccineJlids to be found in spring. They appear to
be adapted to cooler cJimates than the lower mainland of British Columbia as there are
few aphids available when they are first seen. The effect of their predation in reducing
spring aphid numbers can greatly reduce the rate of increase of aphids (Frazer &
Gilbert 1976) and thereby extend the time before pesticides are required. Later in the
season the effects of C. undecimpunctata alone are smalJ because losses from the large
number of predators in alfalfa, at least, are compensatory (Charnov et al. 1976). If C.
undecimpunctata were added to a field without them, their aphid consumption would
simply result in less for the other competing predators with no net increase in aphid
mortality.
Frazer, B.D.; Gilben. N. (1976) Coccinellids and aphids: a quantitative study of the impact of adult ladybirds (Coleoptera: CoccineUidae) preying
on field populations of pea aphids (Homoptera: Aphididae). Journal of the Entomological Society of
British Columbia 73, 33-56.
Charnov, E.; Frazer, B.D.; Gilbert. N.; Raworth. D. (1976) Fishing for aphid - the exploitation of a natural population. JourfllJl of Applied
Ecology 13. 379-389.
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