Metarhizium Pellet Drying Process and Efficiency in Controlling the Coconut Rhinoceros Beetle Larvae

Abstract

The study of drying processes for Metarhizium fungal fresh culture pellets formulation was conducted under laboratory condition, between October 2019 to September 2021. Two methods of drying; dehydrating at 50 ± 2 °C in a hot air oven and dehydrating at 30 ± 3 °C in a 3x3 meter sterile room were compared. The tested samples were collected after 24, 48, 72, and 96 hrs. of drying. the number of conidia, the fungal viability (coony forming unit: CFU) and the moisture content of pellets from both methods were measured. In
conclusion, the best method for drying Metarhizium is the sterile room at 30 ± 3 °C for 24 hrs. which yield highest conidia germination. Pellets obtained from this process was able to control the coconut rhinoceros beetle larvae effectively. There were no statistically significant difference in the number of conidia from both methods at 24 hrs. There were 1.09x10⁸, 3.12x10⁸ and 1.50x108 conidia/ml. from hot air oven method and 2.32x10⁸, 2.55x10⁸ and 2.18x10⁷ conidia/ml. from sterile room method. However, the fungal viability in the sterile room drying method (6.25x10⁷, 5.17x10⁷ and 2.73x10⁸ cfu/g) was higher than a those from hot air oven drying method (3.64x10⁵, 2.65x10⁶ and 1.95x10⁷ cfu/g) in all three tests. The moisture content in a hot air oven drying method (1.91, 2.64 and 1.39 %) was greater than the sterile room drying method (4.77, 3.63 and 3.32 %). There was no significant difference of both
methods in controlling the coconut rhinoceros beetle larvae (100 %). Considering the cost of electricity, the sterile room drying method (37.55 baht /day) costed seven times lower than a hot air oven drying method (268.10 baht/day).