PREVALENCE OF PREDATORS ASSOCIATED WITH ACYRTHOSIPHON-PISUM (HOMOPTERA, APHIDIDAE) AND HYPERA-POSTICA GYLLENHAL (COLEOPTERA, CURCULIONIDAE)DURING GROWTH OF THE 1ST CROP OF ALFALFA

In 1991 and 1992, Coleomegilla maculata Timberlake adults (Coleoptera: Coccinellidae) were the most abundant predators prior to first cuttin g in alfalfa (Medicago sativa L.) from 16 April to 7 June at four loca tions in Iowa. Relative populations of C. maculata adults peaked in 19 92 at more than one per sweep (38 cm diameter sweepnet) in Polk County on 15 May. In 1991 and 1992, densities of C. maculata adults were hig hly correlated (P < 0.1) with varying spatial densities of Hypera post ica Gyllenhal (Coleoptera: Curculionidae) larvae (0.557 < r < 0.919) a nd Acyrthosiphon pisum Harris (Homoptera: Aphididae) (0.379 < r < 0.91 1). Other coccinellid species, including Hippodamia convergens Guerin, H. tredecimpunctata Say, H. parenthesis Say, Coccinella septempunctat a L., Cycloneda munda Say, and Adalia bipunctata L., represented 4.8 a nd 20.5% of the coccinellids collected in 1991 and 1992, respectively. In 1992, when prey density was from 3 to 7 times higher than in 1991, populations of these coccinellid adults were highly correlated with t he density of H. postica larvae (0.324 < r < 0.904) and A. pisum (0.57 3 < r < 0.805) at each location. Hemipteran predators, including unide ntified nabid species and Podisis maculiventrus Say, were relatively r are in alfalfa during this 2-year study. A consistently high correlati on between populations of C. maculata adults and H. postica larvae may reflect the ability of this predator to aggregate to an increasing we evil density, which helps to maintain C. maculata populations in alfal fa fields when A. pisum populations are low. (C) 1994 Academic Press, Inc.