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Virulence of B eauveria brongniartii and B . bassiana against S chizonycha affinis white grubs and adults ( C oleoptera: S carabaeidae)

2014; Wiley; Volume: 139; Issue: 1-2 Linguagem: Inglês

10.1111/jen.12182

1439-0418

Tarryn A. Goble, D. E. Conlong, Martin Hill,

Insect Resistance and Genetics

Abstract Two endemic scarab pests, S chizonycha affinis B oheman and H ypopholis sommeri B urmeister ( C oleoptera: M elolonthinae) have increased in prevalence in the sugarcane producing regions of the K wa Z ulu‐ N atal M idlands, S outh A frica. The crop losses associated with their feeding, the failure of chemical insecticides applied for their control, and the recent discovery of B eauveria brongniartii ( S acc.) Petch ( A scomycota: Cordycipitaceae) epizootics on these pests, have generated interest in the development of a mycoinsecticide targeting adults and larvae of these species. Previous research, using microsatellite markers, identified low levels of genetic diversity among isolates of B . brongniartii collected from two field sites where epizootics occurred. The virulence of 21 of these closely related B . brongniartii isolates and two isolates of B eauveria bassiana ( B alsamo) V uillemin was evaluated. Bioassays were conducted against adults and larvae of S . affinis, and adult T enebrio molitor ( L .) ( C oleoptera: T enebrionidae) as a surrogate test insect. The closely related B . brongniartii isolates varied significantly in their virulence towards both S . affinis (50.1–95% mortality) and T . molitor (39–74% mortality), with a number of these not highly virulent against either of these insect species. Those isolates sharing a haplotype did not vary in virulence. Adults of S . affinis were more susceptible than larvae to isolates of B . brongniartii . The median lethal concentration ( LC 50 ) required to kill half the adult S . affinis test insects was 7.65 × 10 6 conidia per millilitre. Schizonycha affinis second instar larvae had a median survival time of 17.5 days when exposed to some B . brongniartii isolates; however, third instars survived significantly longer with a median of 21 days. Third instars exposed to the highest concentration of B . brongniartii isolate HHWG 1 survived for a median time of 15 days. Bioassays supported the finding that genetically closely related isolates may vary in their virulence, even if they were obtained from the same field epizootics.