CLASSICAL BIOLOGICAL-CONTROL OF THE ACACIA PSYLLID, ACIZZIA UNCATOIDES (HOMOPTERA, PSYLLIDAE), AND PREDATOR-PREY-PLANT INTERACTIONS IN THE SAN-FRANCISCO BAY AREA

Six predaceous insect species were introduced into California to contr ol the acacia psyllid, Acizzia uncatoides (Ferris and Klyver) (Homopte ra: Psyllidae), a pest of Acacia and Albizia spp. planted in landscape s. Just one of these introduced predators, Diomus pumilio Weise (Coleo ptera: Coccinellidae), has established. Although D. pumilio was believ ed to be responsible for providing biological control of the psyllid i n the 1970s, no studies were conducted to document this. We found that psyllid densities on Acacia longifolia Willdenow during 1989-1991 wer e 2 to 20 times lower than before natural enemies were introduced. How ever, the most abundant psyllid predator was Anthocoris nemoralis (F.) (Hemiptera: Anthocoridae), which was not known to be established in C alifornia prior to our study. Psyllid densities increased with increas ed plant growth during the spring, but correlations between acacia gro wth and psyllid density were lower or nonexistent during summer, when psyllid and predator densities were positively correlated. Regression analyses showed that in addition to D. pumilio and A. nemoralis, Adali a bipunctata (L.) (Coleoptera: Coccinellidae) and Hemerobius pacificus Banks (Neuroptera: Hemerobiidae) increase numerically with increasing psyllid populations. Psyllid densities increased when we excluded pre dators from psyllid-infested terminals. Our research demonstrates the importance of documenting classical biological control efforts and may influence projects against other exotic psyllids introduced into Cali fornia landscapes. (C) 1994 Academic Press, Inc.