Pathogenicity statistical analysis of Beauveria bassiana against German cockroach (Blattella germanica)

Abstract

ABSTRACT The pathogenicity of fifteen isolates of Beauveria bassiana against German cockroach (Blattella germanica, Linnaeus, 1767) at three instars was tested and analysed in order to find the best fungal isolate available for the mortality of cockroaches. For the bioassay, three groups of instars were inoculated with a spore suspension, and the subsequent mortality recorded, the response variable was the number of dead cockroaches of a total of 10. For analysing proportion data, three models were analysed: binomial, quasi-binomial, and beta-binomial models. Due overdispersion, binomial model was not appropriate, quasi-binomial and beta-binomial statistical models were suitable for the analysed data. The quasi-binomial model provided a numerically greater standard error than the beta-binomial model although the difference was not significant. All tested isolates of B. bassiana were pathogenic to German cockroaches, although the average mortality percentages differed among isolates. The instar of German cockroach was a significant factor in the pathogenicity of fungal isolates, the pathogenicity of B. bassiana was greater in adult cockroaches and first instars compared with second instars. Four groups of isolates were detected, based on p-values of the hypothesis test of the difference between isolates; Each group of isolates showed statistically the same mortality percentage within the group but differences between groups. The group with the highest percentage of pathogenicity effectiveness against German cockroach (above 74%) only contained isolates derived from Metamasius spinolae at the instar of pupa and larvae, these isolates could be considered for biological control of German cockroach.