A Comparative Analysis of Efficacy of Metarhizium Species for Controlling Brown Planthopper (Nilaparvata lugens) from Different Provinces in Thailand using Survival and Susceptible Infected Models

In this paper, we demonstrate the effectiveness of an entomopathogenic fungus, namely, Metarhizium to reduce environmental problems arising from the use of insecticides. Metarhizium species used in the article include M. anisopliae sensu stricto, M. anisopliae sensu lato, and M. pingshaense. The efficacy of them in controlling the spread of the brown planthopper (BPH) collected from three different regions of Thailand, including Phetchabun Province, Buri Ram Province and Phatthalung Province, was analyzed. Using actual data representing the daily mortality of BPH, we estimated the corrected mortality. In addition, we studied four candidate BPH survival functions, namely the Gompertz model, the Weibull model, the sigmoid model, and the log-logistic model, in order to achieve the best model fitting to the experimental data. As a result, most of the data was best fitted by the log-logistic model. We also used the susceptible infected model to determine the transmission rate from susceptible BPH to infected BPH. Finally, the lethal time formulas and the estimated values of time required for 50% and 90% mortality were obtained using the log-logistic survival and SI models. From the results, the obtained lethal times for both models have the same trends. It is worth noticing that the M. anisopliae sensu lato fungus gave the most effective results in destroying BPH based on the percentages of corrected mortality, lethal time values and transmission rate.