Improvement of fungal formulations for tick control using oils and sunscreens

Abstract

The use of an entomopathogenic fungus as a possible bio-control agent for ticks has been studied in the past with promising results. The major obstacle to the use of entomopathogenic fungi in the field is the rapid inactivation of the spores by ultra-violet (UV) radiation. Attempts to protect entomopathogenic fungi from damage by UV radiation have not been very successful. In this paper we present preliminary results of a new approach of protecting spores ofMetarhizium anisopliae formulated in water and oil emulsion, using sunscreens (Everysun® and E45 Sun Block 50®). This strategy involved adding 1 % and 3 % sunscreen with sun protection factor (SPF) values of 30 (Everysun®) and SPF50 (E45 Sun Block 50®) for spore survival. Spores formulated in water and oil and exposed to UV radiation without addition of sunscreen were observed to have low germination in Sabourauds Dextrose Agar (SDA). When 0.1 m spore suspension of 2 × 102/m was plated, only 4 and 10 colony-forming units (CFUs) survived in water and oil formulations, after 1 hr of exposure to UV radiation, respectively. Total viability was completely lost after 4 hours of exposure in water and 5 hours in oil, respectively. However, formulations to which sunscreens were added retained viability even after 5 hours of exposure to the UV radiation. Sunscreen with SPF50 offered better protection against UV radiation damage than SPF30. Addition of 3 % sunscreen SPF50 offered the highest protection, with 5 and 8 CFUs surviving in water and oil, respectively, after 5 hours of radiation exposure. Addition of 3 % sunscreen to either formulation resulted in higher spore survival than the addition of 1 % sunscreen. In both formulations, spore survival was consistently higher in oil than in water formulations after exposure to UV radiation.