Beauvaria bassiana is a common soil borne fungus that occurs worldwide. Two strains of this fungus are commercially available, Naturalis O and Botanigard. The fungus secretes enzymes which dissolve the insect's cuticle. After it enters the insect's body, the fungus produces a toxin that weakens the insect's immune system. Thorough spray coverage is needed so that the fungal spores contact the targeted insect pest and begin the infection process.
Aphids are difficult to control with insecticides for a number of reasons.
Control failures may be due to poor spray techniques, inadequate coverage or high pH in the spray tank. Among green peach aphid populations, resistance to organophosphates, carbamates and pyrethroid insecticides has been reported. Winged forms of the melon aphid are more resistant to organophosphate pesticides than wingless forms. Different strains of aphids may be resistant to different materials. Use pest-infested plants as indicators to monitor the effectiveness of treatments in your individual situation.