Location: Emerging Pests and Pathogens ResearchTitle: Laboratory and field efficacy of entomopathogenic fungi for the management of the sweetpotato weevil, Cylas formicarius (Coleoptera: Brentidae) Author
Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2014
Publication Date: 8/8/2014
Citation: Reddy, G.V., Zhao, Z., Humber, R.A. 2014. Laboratory and field efficacy of entomopathogenic fungi for the management of the sweetpotato weevil, Cylas formicarius (Coleoptera: Brentidae) Journal of Invertebrate Pathology. 122:10-5. Interpretive Summary: This study is one of the first looking at biorational biological control strategies to apply against a serious weevil pest of sweet potatoes in the Marianas Islands. Commercial formulations of two fungi–Metarhizium brunneum and Beauveria bassiana–and the plant-derived pesticides azadirachtin and spinosad were tested individually and in all combinations for their efficacy in controlling sweetpotato weevil (Cylas formicarius). It was found that the best pest control and highest eventual yields of the crop were obtained from a mixture of both fungi at half of each fungus’ recommended rate. There are few such demonstrations of the superior activity of applications of combinations of two biocontrol fungi proving to be the superior strategy for controlling a field crop pest. Such a combination of fungi may prove to be useful in other similarly warm and humid locations as the Marianas Islands with other insect pests on other field crops, but prior experiences with these fungi suggest that this combination is less likely to be useful against pests of crops growing in more temperate locations.
Technical Abstract: 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 Marianas 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 grams 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.