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 control the acacia psyllid, Acizzia uncatoides (Ferris and Klyver) (Homoptera: Psyllidae), a pest of Acacia and Albizia spp. planted in landscapes. Just one of these introduced predators, Diomus pumilio Weise (Coleoptera: Coccinellidae), has established. Although D. pumilio was believed to be responsible for providing biological control of the psyllid in the 1970s, no studies were conducted to document this. We found that psyllid densities on Acacia longifolia Willdenow during 1989-1991 were 2 to 20 times lower than before natural enemies were introduced. However, the most abundant psyllid predator was Anthocoris nemoralis (F.) (Hemiptera: Anthocoridae), which was not known to be established in California prior to our study. Psyllid densities increased with increased plant growth during the spring, but correlations between acacia growth 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, Adalia bipunctata (L.) (Coleoptera: Coccinellidae) and Hemerobius pacificus Banks (Neuroptera: Hemerobiidae) increase numerically with increasing psyllid populations. Psyllid densities increased when we excluded predators 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 California landscapes.