The susceptibilities of five thrips species, Frankliniella intonsa, F. occidentalis, Thrips coloratus, T. hawaiiensis, and T. tabaci, to three isolates of an entomopathogenic fungus, Beauveria bassiana (isolates AZA38, GOM03, and KOG02), were investigated under laboratory conditions. Among the three fungal isolates, the five thrips species were the most susceptible to isolate KOG02 when inoculated with conidial suspensions at a concentration of 1ϫ10 7 conidia/ml. Females of F. intonsa were more susceptible to the fungi than males, while males of F. occidentalis and T. coloratus were more susceptible than females. Both males and females of T. hawaiiensis were highly susceptible to isolate KOG02. T. tabaci was highly susceptible to isolate KOG02, even by inoculation of the conidial suspension at a concentration of 1ϫ10 6 conidia/ml. Although isolates AZA38 and GOM03 exhibited weaker pathogenicity to the five thrips species than did isolate KOG02, the gross mortality increased significantly with the inoculation of these two isolates as compared with the control.
The insecticidal activity of Beauveria bassiana GHA derived from a commercial mycoinsecticide BotaniGard ES against Frankliniella occidentalis was determined in a bioassay by dipping the female adults into a conidial suspension. The 90% lethal concentration of B. bassiana GHA was estimated to be 9.7 9 10 6 conidia/ml. The lethal times for achieving 90% mortality of thrips inoculated with a 1/500-diluted solution of BotaniGard ES and a 10 7.5 (3.16 9 10 7 ) conidia/ml suspension of B. bassiana GHA were estimated to be five and six days, respectively. When the treated thrips were exposed to a high relative humidity (RH) of over 99% for various periods and then transferred to 60% RH, the requisite lengths of the high-humidity period to achieve 90% mortality of the thrips at six days after inoculation were estimated to be 46 and 47 h in BotaniGard ES and B. bassiana GHA, respectively. Fungal multiplication in the thrips was detected between 48 to 60 h after inoculation by measuring Beauveria-specific DNA in the host following inoculation with a B. bassiana GHA suspension of 10 7.5 conidia/ml using a real-time quantitative PCR. The mycelial growth in the host hemocoel was not influenced by the low-humidity condition.
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