Evaluation of Field Releases of Laboratory-Reared Larval and Adult Bactra verutana (Lepidoptera: Tortricidae) for Control of Purple Nutsedge 1

Abstract

The native tortricid moth, Bactra verutana Zeller, was evaluated for efficacy in large-scale releases for the biological control of purple nutsedge, Cyperus rotundus L., and yellow nutsedge, C. esculentus L. Adults, first-stage larvae, and fourth-stage, 13-day-old larvae were released. When 4,800 to 8,200 adults (1:1 sex ratio) were released at one point, 50% of the plants were attacked at all six sites out to 5 m from the points of release and at one site out to 10 m. Moths flew only when disturbed during the hours of light but flew freely after dark. They mated at night or at dawn. Although all of fourth-stage larvae attacked dense nutsedge populations averaging 83 shoots per 9.29 dm 2 , only 30% attacked sparse populations averaging 8 shoots per 9.29 dm 2 With sparse growth averaging 1.4 or 7.0 shoots per m of row, first-stage larvae on corncob grits, released in a narrow band, attacked 57 and 46%, respectively, of the shoots up to 5 cm away. When the corncob grits were broadcast, first-stage larvae increased infestation by 30 to 87% over untreated areas. Regardless of the stage of B. verutana upon release, the degree of control depended on the age and condition of the plants. Rates of infestation were high only when the majority of the shoots were in a vigorous growing condition 10 to 21 days old.