Effect of Planting Coleus blumei on Insect Populations in Taro (Colocasia esculenta) Fields in American Samoa

Abstract

In a Rapid Rural Appraisal Survey, conducted in American Samoa in November, 1990, farmers reported that planting Coleus blumei (pate in Samoan) with taro (Colocasia esculenta) kept armyworms (Spodoptera litura) and/or planthoppers (Tarophagus proserpina) from their taro fields. Two experiments were conducted at the Land Grant Station in American Samoa from May to November, 1991 and February to August 1992, respectively, to test this hypothesis. In the first study, semi-monthly insect counts were made on two fields, one planted with Coleus blumei in the center and one without the Coleus. Insect data were collected from each of eight quadrates surrounding the Coleus and at three distances away from the center of the field. There were no significant differences in pest incidence between Coleus and non-Coleus fields. Results indicated a slight trend toward fewer armyworms and planthoppers in the field planted with Coleus. A second study compared insect incidence in eight taro plots, four with and four without a border of Coleus. Insect counts were collected semi-monthly. No statistical differences were found between insect incidence in the two types of plots. There was a trend toward more armyworms in the non-Coleus plot. Future studies will focus on examining other environmental factors that might influence taro pest and/or parasite incidence, as well as modifications in experimental design.