Flavone content of silks from commercial corn hybrids and growth responses of corn earworm (Helicoverpa zea) larvae fed silk diets

摘要

Silks of commercial corn hybrids (ranging in maturity from 60-65 d to mid-silk) were evaluated against feeding response of the corn earworm, Helicoverpa tea (Boddie), larvae. Flavone (maysin, chlorogenic acid, and apimaysin plus 3'methoxymaysin) content was determined for each hybrid from 2-d-old pollinated silks. Significant (P less than or equal to 0.05) differences among hybrids were found in the weight of larvae fed silk diets of the commercial hybrids. In 50 out of 74 comparisons, larvae that fed on silk diets with formalin weighed significantly (P less than or equal to 0.05) more than those that fed on silk diets without formalin. Varying concentrations of formalin used in the diet up to 10X did not appear to react with maysin: maysin and maysin content were identical after the formalin was added to maysin, indicating no reaction had occurred. Consistent, significant (P less than or equal to 0.05) negative correlations were found between weight of larvae feeding on silk diets with and without formalin and maysin and chlorogenic acid among the four maturity groups tested but not for apimaysin plus 3'methoxymaysin. Several hybrids (Hyperformer HS9843, Stanford S88B, N C + X6485, Zimmerman Z63W, Pioneer 3140, Ag America 6714, and ICI Garst H8285) possessed silks that exhibited high antibiosis against larvae of the corn earworm. Silks of some hybrids did not contain sufficient amounts of maysin or other flavones to account for the observed reduction in growth of larvae, e.g., N C + X6485 and Zimmerman Z63W in the short-season hybrids and SSI UTN 318 in the preliminary-season hybrids. Silks of Zimmerman Z63W produced small larvae and had less maysin and apimaysin + 3'methoxymaysin than silks of the susceptible standard Stowell's Evergreen.