Fungal Control for Root-Eating Insects

Root-eating insects could soon be eating themselves sick—if their favorite food has been treated with a fungal biocontrol agent.

Agricultural Research Service (ARS) scientists in Corvallis, Ore., are discovering new ways to use fungal spores for controlling the black vine weevil and other root-eating nursery pests.

Many biological control agents are expensive and ineffective against root-eating larvae. However, entomopathogenic fungi—those that cause diseases in insects—have proved successful.

Current control methods involve applying large amounts of entomopathogenic fungi to the soil in which at-risk plants grow. This approach is both costly and inefficient. ARS entomologist Denny Bruck has discovered that using plant roots as an underground "delivery system" for the fungi is cheaper and more effective than broad distribution.

He and his colleagues in the Corvallis-based ARS Horticultural Crops Research Unit tested several fungal strains and found that some of them thrived in the area immediately surrounding a plant's roots. In fact, some fungal populations were 10 times denser there than in the surrounding bulk soil.

In one study, Bruck and his colleagues dipped plant roots in solutions containing spores of Metarhizium anisopliae, a fungus that occurs naturally in fields but not in container-grown plants. They observed that black vine weevil larvae died after eating the fungus-treated roots.

Dipping roots in entomopathogenic fungal solutions may prove to be economical and efficient, because growers would only need to treat that specific area.

Another study demonstrated that black vine weevil larvae actually prefer the colonized plant roots, so they are more likely to snack on roots that will harm them. Perfecting a fungal solution to root-eating pests could potentially save the West Coast nursery industry millions of dollars every year.

Read more about the research in the August 2007 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.