CONSTRAINTS ON THE EFFECTIVENESS OF PSYLLAEPHAGUS BLITEUS (HYMENOPTERA: ENCYRTIDAE), A BIOLOGICAL CONTROL AGENT FOR THE RED-GUM LERP PSYLLID (HEMIPTERA: PSYLLOIDEA) IN CALIFORNIA K.R. Sime, K.M. Daane, D.L. Dahlsten, J.W. Andrews Jr., D. Rowney; Division of Insect Biology, University of California at Berkeley, CA 94720, U.S.A. ABSTRACT Psyllaephagus bliteus Riek (Hymenoptera: Encyrtidae) was released throughout California in 2000 and 2001 to control the red-gum lerp psyllid, Glycaspis brimblecombei Moore (Hemiptera: Psylloidea). A Eucalyptus feeder native to Australia, G. brimblecombei was first discovered near Los Angeles in 1998 and had spread throughout the state by 2000. The wasp established and quickly became effective in coastal areas but to date has had less impact inland. The experiments discussed herein were designed to address this problem and collect basic biological information that would improve the control program. The specific objectives were to determine adult longevity and fecundity, to determine host-stage preference for oviposition, and to compare parasitism rates in the field at inland and coastal sites. Maximum fecundity occurs at one to three weeks of age. Most eggs are recovered from 3 rd instars, but oviposition is attempted into 3 rd , 4 th , and 5 th instars equally. Observations of host-handling behavior suggest that the large lerps of 4 th and 5 th instars impede oviposition. In 2003, parasitism rates were lower at inland than at coastal sites at the same latitude; cage trials conducted during the summer suggest that the adults do not survive long and lay fewer eggs inland. We hypothesize that high summer temperatures inland limit the effectiveness of this wasp. INTRODUCTION Psyllaephagus Ashmead (Hymenoptera: Encyrtidae) is a cosmopolitan genus of parasitic wasps containing over 200 described species and perhaps as many as 1000 in all (Noyes & Hanson, 1996). Australian Psyllaephagus have recently attracted attention in classical biological control programs aimed at psyllid pests of various Eucalyptus species in California, Mexico, and the British Isles (Chauzat, 2002; Dahlsten et al., 1998; Paine et al., 2000). The Australian red-gum lerp psyllid, Glycaspis brimblecombei Moore (Hemiptera: Psylloidea), was first discovered on red-gum trees (Myrtaceae: Eucalyptus camaldulensis Dehnh.) in Los Angeles County in 1998 and had spread throughout California by 2000 (Brennan et al., 1999; Paine & Millar, 2002) and Mexico by 2002 (J. Guerra, pers. comm.). The nymphs of G. brimblecombei, like those of other Glycaspis species, construct shelters called lerps from excreted carbohydrates and proteins (Moore, 1961). The accumulation of the sticky lerps on leaves and underneath infested trees creates a nuisance; heavy infestations lead to defoliation, branch dieback, and occasionally the death of trees (Paine et al., 2000). Psyllaephagus bliteus Riek was released throughout California in 2000 and 2001 to control G. brimblecombei after quarantine testing indicated that it would specifically attack this host. The wasp established and quickly became effective in coastal areas but to date has had less impact in the Central Valley (Daane et al., in prep.). The goals of this study were to address this problem and to collect basic biological information that would improve the control program. MATERIALS AND METHODS Sources of insects and plants The psyllids used in these studies were taken from a colony maintained in glasshouse facilities on the U.C. Berkeley campus (20-26°C). The colony originated with psyllids collected on infested red gums in Alameda and Sacramento Counties, California. The psyllids were reared on small potted red-gum trees (0.5-1 m tall). The wasps were reared from infested foliage cut from red gums in the Ardenwood Regional Preserve in Alameda County. This population originated with the releases in 2000 and 2001 of reared wasps from stock collected in southern Australia in 1999. Host-stage preference for oviposition For each trial, 3 or 4 psyllid-infested red gums were placed in a cloth-sided cage (96 cm × 32 cm × 45 cm) kept at ambient room temperature (about 25°C) under fluorescent lighting. The trees were selected so that 300-500 psyllids, of all 5 stages, were present in the cage. At the start of a trial, 15-20 female wasps and 4-5 males were released into the cage. After 24 h, the wasps were removed. All of the psyllids were then transferred to 70% ethanol. Five trials were conducted. To determine the ages of the psyllids and whether or not they were parasitized, the psyllids were transferred to a clearing solution of chloralphenol. 141