Virulence Screening of Malaysia-Isolated Metarhizium anisopliae against Rhipicephalus microplus

Rhipicephalus microplus poses a significant challenge to the livestock industry, leading to substantial economic burdens. Traditionally, chemical acaricides have been the primary management strategy; however, their indiscriminate use has led to resistance, environmental contamination, and health risks. Therefore, there is growing interest in exploring alternative approaches, such as entomopathogenic fungi like Metarhizium anisopliae . This study aimed to evaluate the effectiveness of M. anisopliae isolates from Malaysia against R. microplus using the Adult Immersion Test protocol. Engorged female ticks were utilized in the bioassay. The experiment involved applying M. anisopliae isolates (1518, 1521, 1522, PR1, HSAH5, and GT3) at a concentration of 10 ⁸ through tick immersion. Mortality rates were monitored for 14 days, with experiments conducted in triplicate. Result showed that PR1 exhibited the highest virulence, causing 83.33% mortality within 14 days. There was no significant difference between the isolates in their ability to cause tick mortality. However, probit analysis revealed that PR1 have the shortest LT ₅₀ and LT ₉₀ with 10.03 days and 14.69 days, respectively. Correlation analysis revealed a significant moderate negative correlation between tick size and mortality and not significant between germination rate and tick mortality. These findings emphasize the influence of tick size on tick mortality. Although no isolate achieved 100% mortality, PR1 was notably effective, killing the highest percentage of ticks quickly and significantly reducing egg production compared to the control and other isolates. Overall, this study underscores the potential of Malaysia-isolated M. anisopliae in the management of adult R. microplus , offering insights into alternative strategies for pest control in the livestock sector.