Field Release in Florida ofDiaphorencyrtus aligarhensis(Hymenoptera: Encyrtidae), an Endoparasitoid ofDiaphorina citri(Homoptera: Psyllidae), from Mainland China

Abstract

The Asian citrus psyllid, Diaphorina citri Kuy awama (Hemiptera: Psyllidae), is a serious pest of citrus that vectors the phloem-limited non culturable bacterium Candidatus Liberibacter asiaticus Jagoueix, Bove and Gamier (Jagoueix et al. 1994). The resulting disease is commonly referred to as citrus greening or huanglongbing (HLB) (Bove 2006). The psyllid was first reported from Florida in 1998 and citrus greening in 2005 (Halbert 1998, 2005). Two species specific parasitic wasps, Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) and Diaphorencyrtus aligarhensis (Shafee, Alam and Argarwal) (Hymenoptera: Encyrtidae), were imported into Florida from Taiwan and Vietnam and released beginning in 1999 as biological con trol agents for D. citri (Hoy & Nguyen 1998). Tam arixia radiata has established in Florida (Qureshi et al. 2009), while D. aligarhensis has not. An additional population of D. aligarhensis was collected in Guangdong province, China and sent to Gainesville, Florida in 2006. A colony was initiated in the Maximum Security Room of the Florida Biological Control Laboratory, Florida De partment of Agriculture and Consumer Services, Division of Plant Industry. Parasitoids were held in quarantine through 20 generations before re lease permitting was complete and mass rearing began. Sixty-seven releases were made at 10 sites in 6 Florida counties (Alachua, Collier, DeSoto, Hendry, Orange and Polk) between 8/2007 and 10/2009, deploying a total of approximately 11,100 wasps (Table 1). Sites included commer cial and private citrus groves as well as Murraya paniculata hedges. Wasps were either tapped out of holding tubes directly onto emerging plant shoots infested with immature psyllids or were released into cages consisting of fine mesh bags tied around new shoots infested with nymphs. Shoots were carefully inspected and predators removed prior to tying cages closed. Mesh size al lowed parasitoid wasps to move freely in or out of the cage while preventing most predaceous in sects from entering. Released wasps successfully parasitized nymphs in the field and second generation wasps emerged. Evidence of this includes laboratory emergence of adult wasps from field clippings, D. aligarhensis parasitized mummies found on shoots covered with mesh cages, and several adult wasps sighted foraging on D. citri infested M. paniculata plants (Table 1). All citrus groves used for wasp release, including certified organic groves, used pesticide sprays dur ing the release period. The use of insecticides target ing D. citri likely reduced both psyllid and natural enemy populations (Qureshi & Stansly 2007). Mur raya paniculata release sites were not subjected to any form of insect control, although occasional plant trimming by the property owners removed much of the new soft growth that I). citri uses for feeding and oviposition, consequently leaving few imma ture hosts for D. aligarhensis reproduction. Adult psyllids were present at all locations throughout the release period although their incidence appeared to decline over the >2 year release period, likely from increased insecticide use to reduce the spread of citrus greening dis ease. During many trips to various locations for parasitoid release there was little to no host plant flush or immature psyllids present, particularly during late summer and fall. Tamarixia radiata wasps were present at all release sites utilized in this study. Through the combined effect of host feeding and parasitism, a single female T. radiata can kill nearly twice as many psyllids in her lifetime as can a female D. aligarhensis (500 vs. 280, respectively) (Chien 1995). Additionally, T. radiata has a shorter gen eration time and a higher reproductive rate (Skel ley & Hoy 2004). Furthermore, any hosts parasit ized by T. radiata before or within 5 d following parasitism by D. aligarhensis will result in T. radiata offspring (E. R. unpublished data). Thus, competition with T. radiata could present another impediment to establishment of D. aligarhensis. Coccinellid predators were seen at all release sites. Generalist predators can induce high lev els of psyllid mortality (Qureshi & Stansly 2009). Curinus coeruleus Mulsant, Cycloneda sanguinea (L.) and Harmonia axyridis Pallas readily con sumed D. citri nymphs parasitized by D. aligar hensis (E. R. unpublished data) causing wasp mortality.