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Biological control of Bactericera cockerelli using a combination of parasitoids and pathogens has potential. However, their combined use could result in complex multitrophic interactions, the outcomes of which are uncertain. In this study we evaluated the effects of applications of two Beauveria bassiana isolates (pathogen) on the parasitoid Tamarixia triozae during its development on the host, B. cockerelli . Three concentrations (LC 20 , LC 50 and LC 90 values against B. cockerelli ) of the fungal isolates BB40 and GHA were applied to 4th instar B. cockerelli nymphs that had been successfully parasitized by T. triozae 3, 5, 8 or 12 days earlier at 25 °C. The greatest infection of T. triozae was observed when the calculated LC 90 was inoculated, regardless of isolate, and when the parasitoids were 3–5 days old. The lowest infection of T. triozae was observed when they were 8 and 12 days old regardless of isolate or conidial concentration. The highest parasitoid emergence was achieved in the untreated control compared with all other treatments and combinations tested. Within treatments, the highest parasitoid emergence was obtained at the lowest B. bassiana concentration tested and when the pathogen was applied to B. cockerelli supporting 12 day-old parasitoids. Longevity of adult parasitoids that had emerged from B. cockerelli nymphs was greatest in the control treatment, followed by those from nymphs treated with GHA when applied to B. cockerelli supporting 12 day-old parasitoids. In conclusion, biological control of B. cockerelli may require the synchronized use of high B. bassiana concentrations, applied only on T. triozae late pupal stage (8–12 days of development), in order to allow the parasitoid to survive and also achieve good overall pest control. [ABSTRACT FROM AUTHOR]

Bactericera cockerelli (Sulc.) is an important pest of solanaceous crops and a vector of the pathogen Candidatus Liberibacter psyllaurous . Biocontrol of this pest has been attempted with either entomopathogenic fungi or the parasitoid Tamarixia triozae (Burks), but prior to this study, their potential impact in combination had not been studied. The aim of the present study was to evaluate T. triozae parasitism rates on B. cockerelli nymphs that were previously infected for different periods of time by three isolates of Beauveria bassiana (Bals.) Vuill. Two native isolates (BB40 and BB42) and one commercial isolate (GHA) were used. The virulence of these isolates was first estimated against B. cockerelli and T. triozae . LC 50 values for the native isolates BB40 and BB42 against B. cockerelli were 9.5 × 10 5 and 2.42 × 10 6 conidia mL −1 respectively; they were significantly more virulent than isolate GHA with an LC 50 of 1.97 × 10 7 conidia mL −1 . However, isolate GHA was significantly more virulent against T. triozae with an LC 50 of 1.11 × 10 7 conidia mL −1 compared with LC 50 s of 1.49 × 10 7 and 1.14 × 10 8 conidia mL −1 for the native isolates BB40 and BB42 respectively. Groups of nymphs were then inoculated with LC 20 , LC 50 or LC 90 concentrations of each isolate and presented to T. triozae as hosts either on the day of inoculation or 1, 2, 3, 4, 5, 6 days after inoculation. Subsequent levels of parasitism were recorded. Overall, parasitism rates were similar in inoculated and control nymphs. No parasitism occurred in nymphs 6 days after fungal inoculation. Parasitoids used to parasitize uninoculated B. cockerelli nymphs survived significantly longer (7.8 days) than parasitoids that had been used to parasitize fungus-inoculated nymphs (7.3 days). This suggests an inability of the parasitoid to avoid infection when foraging on inoculated nymphs. In conclusion, although the parasitism rate in control and fungus-treated nymphs was similar, suggesting a combination of both biological control agents is possible, we believe there are also negative implications for the parasitoid because its survival was greatly reduced after attacking infected nymphs. [ABSTRACT FROM AUTHOR]