Dennis R. Ring, Diaz, Rodrigo
Lori Moshman, Rodrigo Diaz and Dennis Ring
The insecticide Beauveria bassiana is a fungus that occurs naturally in soil. Many strains exist and can vary in host range, pathogenicity (ability to infect a host) and virulence (ability to multiply in the host). The fungus was first isolated in 1835 by Italian scientist Agostino Bassi, who found that it killed and mummified silkworm larvae in what was called muscardine disease. The first commercial formulations of B. bassiana were developed in 1995 and sold under the trade names BotaniGard, Mycotrol and Naturalis. Additional strains were subsequently isolated and made available commercially.
B. bassiana is a contact insecticide, meaning its spores must physically contact the insect cuticle to be effective. Thorough and even coverage is therefore important when making applications. It is not necessary for the insect to ingest B. bassiana because the fungal spores adhere to the insect and penetrate the body cavity when they germinate. Once inside, chemicals are produced, including the toxin beauvericin and the antibiotic oosporein, that weaken the host’s immune system and outcompete intestinal bacteria. White mold may grow out of the insect’s body after it has died, but mold growth is not required to achieve control.
As a generalist feeder, B. bassiana controls all life stages of leaf-feeding insects including common pests such as aphids, thrips, whiteflies, mealybugs, caterpillars and beetles. Immature stages tend to be more susceptible than adults. Spray formulations can be applied in greenhouse or field settings, and on ornamental or edible crops. Efficacy depends on climatic conditions; the greatest control occurs within 68-86 F and above 60 percent relative humidity. In greenhouses, control may be reached in three to seven days, but it is not uncommon for control to take seven to 10 days in field settings. Repeat applications are recommended every five to seven days until a desired level of control is reached.
A commercial suspension of B. bassiana spores has a shelf life of one year when stored at room temperature and longer when stored in the refrigerator. It should not be stored below 0 F or above 85 F.Spray mixes should be applied as soon as possible after mixing because spores cannot survive in water for more than 24 hours and are susceptible to degradation from UV light. Spores remain viable for a longer time when applied to leaf undersides or in the evening due to reduced sunlight exposure.
B. bassiana is considered safe for beneficial insects, although it is recommended to avoid spraying directly in areas where bees are actively foraging. If bees are contacted directly, they can bring fungal spores back to the hive and infect the susceptible brood.
Some formulations are OMRI (Organic Materials Review Institute) approved for organic pest control. B. bassiana may be tank mixed with other insecticides according to label regulations but should never be mixed with fungicides.
Lori Moshman is a former graduate assistant, Rodrigo Diaz is an assistant professor, and Dennis Ring is a professor, all in the Department of Entomology.
(This article appears in the winter 2018 issue of Louisiana Agriculture.)