(5779) BEESLEY, C, 1974. Simulated field predation of single-prey (Culex peus) and alternative-prey (Culex peus: Chrionomus sp. 51) by Anax junius Drury (Odonata: Aeschnidae). Proc. Mosq. Coni. Assoc. 42: 73-76. — (Contra Costa Mosquito Abatement Distr., 1330 Concord Ave., Concord, CA 94520, USA). Simulated-field predation tests with A. junius were conducted in enclosed-unit fiberglass tubs, with both single and alternative prey available (Culex peus: C. peus and Chironomus species 51 respectively). C. peus egg rafts and C. sp. 51 egg masses were periodically introduced to sustain prey population and daily prey emergence was recorded. Predators were initially introduced at 3 densities and monitored at 2-week intervals for growth and population size. Results showed that dragonfly larvae controlled mosquito populations at all 3 densities in the single, and the 2 higher densities in the alternative prey tests. In both tests, the higher predator densities were seen to reduce prey populations in a shorter period of time. However, with subsequent mosquito reduction predator populations also declined to a few remaining large larvae. These reduced larval populations continued to maintain control of the mosquitos. With the presence of an alternative prey, predator populations still declined after mosquito reduction, but remained significantly higher than in the single-prey tests. Larvae exercised no significant control over the midge populations.