GROWTH-INHIBITION OF CORN-EARWORM (LEPIDOPTERA, NOCTUIDAE) LARVAE REARED ON RESISTANT CORN SILK DIETS

Laboratory studies were conducted to determine whether the growth inhi bition response of corn earworm, Helicoverpa zea (Boddie), larvae on c orn silks is a result of a feeding deterrent or other factors. Neonate s and 4th and 5th instars were fed either pinto bean diet (control), a mixture of silks of 'Stowell's Evergreen' (susceptible), or 'Zapalote Chico 2451# P(C3)' (resistant) corn. The silks of Zapalote Chico inhi bited growth, extended development time, and reduced weight of pupae w hen neonate and 4th instars were tested. Both consumption and amount o f feces were less for neonates fed resistant silk diets, but not for 4 th and 5th instars. Consumption and amount of feces excreted by 4th an d 5th instars on both resistant and susceptible silk diets were greate r than that of the pinto bean diet. The amount of protein in the feces excreted by 4th and 5th instars reared on resistant silk diets was su bstantially more than the amount of protein in the feces excreted by l arvae reared on control diets. The percentage of protein:feces was sub stantially higher for Zapalote Chico (91.5%) than for Stowell's Evergr een, the susceptible entry (75.1%). The growth inhibition factor in re sistant silks is likely caused by an antinutritive factor causing the larvae to excrete large amounts of protein.