Functional and behavioral response of Tamarixia radiata (Hymenoptera: Eulophidae) to different densities of its host, Diaphorina citri (Hemiptera: Psyllidae)

It has been claimed that success of parasitoids as biological control agents can be predicted by response to increasing host densities, termed “functional response” as mediated by so-called “searching time” and “attack rate” first characterized by the Holling Disk Equation and later refined by Rogers (1972). How do these parameters relate to actual behavior exhibited by the female wasp in the presence hosts?  A functional response was evaluated by holding pairs of three-day-old T. radiata in 50 ML centrifuge tubes with access to an M. paniculata shoot infested with 10, 20, 30, 40, 50, or 60, 4^th instar psyllid nymphs changed every 24 h. Parasitism was highest with 10 hosts at 43% and least at 18.5% with 60 hosts.  Superparasistim showed the opposite trend, being highest (39.4%) at the lowest host density. Results conformed to a Type II functional response with attack rate (a’) estimated by the Rogers equation at 9.0 ± 1.3 cm² / hr and handling time (T_h) of 50.4± 3.6 min/ host.  Behaviors of individual 3-day-old females in petri dishes with the same 6 host densities were recorded using Observer software for 30 minutes with much different results: handling time (3.1 ± 0.74 min/ host), defined as probing + oviposition, and attack rate (333 ± 72.6 cm² /hr) calculated from the Rogers equation which equates encounters to the product of searching time, host density and attack rate. The search continues for relationships between functional response, parasitoid behavior and biological control success.