Functional Response of Tamarixia radiata (Hymenoptera: Eulophidae) to Densities of Its Host, Diaphorina citri (Hemiptera: Psylloidea)

Tamarixia radiata (Waterston) (Hymenoptera: Eulophidae) spread rapidly in Florida following first release in 1999 for control of the Asian citrus psyllid Diaphorina citri (Kuwayama) (Hemiptera: Psylloidea). However, rapid spread of huanglongbing (HLB) has created a need for more effective biological control through augmentation and thus the necessity to better understand the potential of this parasitoid. Therefore, the functional response of fecundity to host density was evaluated to provide a possible indicator of success and useful information for mass rearing of T. radiata. The experimental unit consisted of a single 3-d-old female in a centrifuge tube with a young Murraya paniculata (L.) Jack (Rutaceae) shoot infested with a range of 1-60 fourth-instar D. citri nymphs. Shoots were changed daily for 5 d and the nymphs containing one or more parasitoid eggs noted. The number of hosts parasitized daily increased from 0.7 to 11.2 on average as host density increased from 1 to 40, above which it remained relatively constant. Percent parasitism was as high as 73.3% at density 1, but decreased at greater host densities. A random parasite equation was selected as the best-fit model, from which we obtained an attack coefficient of 12.7 cm(2)/h, and handling time of 0.873 hour per host. We proposed the term adjusted searching efficiency to express the attack coefficient as a function of searching area. Similarities and differences with previous studies are discussed, as well as the need to reconcile parameters with actual behavior of T. radiata.