The effects of oils on germination of Beauveria bassiana (Balsamo) Vuillemin and its infection against the oil palm bagworm, Metisa plana (Walker).

This study reports the effects of oils on the conidial germination of four strains of Beauveria bassiana (Balsamo) Vuillemin (F1, F5, F8 and F10) and their infectivity against the larvae of the oil palm bagworm, Metisa plana Walker. The effects of the oils and age of the conidia on the germination of the conidia were examined in the first experiment. Of the five oils tested, soyabean oil and paraffin gave the highest germination for both two- and four-week-old conidia. Palm and corn oils completely inhibited the conidial germination. Germination was influenced by the age of conidia with the mature conidia germinating better than the younger conidia. The pathogenicity of all the four strains of B. bassiana conidia formulated in soyabean oil against the larvae of M. plana revealed that more than 95% mortality at 10 days after treatment. Although Strain F5 produced the lowest LT 50 (2.6 days), based on the mortality rate and percentage infection, Strain F10 was the more pathogenic. The short (254 nm) ultraviolet radiation was more detrimental to the conidia compared to the long (365 nm) ultraviolet radiation. Soyabean and paraffin oils gave a similar level of protection to the conidia but oil with 1% (w/v) sunscreen gave significantly better protection. Strain F10 was more stable than Strain F5 to both wavelengths of ultraviolet radiation. B. bassiana conidia formulated in oil plus 1% sunscreen and oil alone caused about 12 and 15 times higher mortality against the larvae of M. plana than the water formulation. The advantages of using oil over water for the formulation of B. bassiana to control M. plana in the field are discussed.