Laboratory and field efficacy of entomopathogenic fungi for the management of the sweetpotato weevil, Cylas formicarius (Coleoptera: Brentidae)

- The sweetpotato weevil is an important pest of sweet potatoes.
- The effect of fungal formulations on sweetpotato weevil was studied.
- The Beauveria bassiana + Metarhizium brunneum combination was the most successful treatment.
- The highest number of insect cadavers was recorded in the plots treated with dual fungal formulation.

The sweetpotato weevil, Cylas formicarius (F.) (Coleoptera: Brentidae), is one of the most important pests of sweet potatoes in the world. With free trade between the United States and the U.S.-controlled Mariana Islands, C. formicarius has spread along with this commodity. Because of the cryptic nature of the larvae and nocturnal activity of the adults, and the cancellation of long-residual pesticides, this pest has become increasingly difficult to control. Therefore, the present study sought to explore and to compare the effectiveness of Metarhizium brunneum F52 (90 ml a.i./ha), Beauveria bassiana GHA (40 ml a.i./ha), spinosad (90 g a.i./ha), azadirachtin (1484 ml a.i./ha), B. bassiana + M. brunneum (20 ml a.i./ha + 45 ml a.i./ha), B. bassiana + azadirachtin (20 ml a.i./ha + 742 ml a.i./ha), B. bassiana + spinosad (20 ml a.i./ha + 45 ml a.i./ha), M. brunneum + azadirachtin (45 ml a.i./ha + 742 ml a.i./ha) and M. brunneum + spinosad (45 ml a.i./ha + 45 grams a.i./ha) in controlling this pest in both the laboratory and the field. The treatment with B. bassiana + M. brunneum was the most effective in reducing tuber damage by C. formicarius, producing the highest yields. The most adult cadavers were found in plots treated with the combination of two fungi. This combined fungal formulation appears to be appropriate for the practical control of C. formicarius on sweet potatoes.