EFFECTS OF A RESISTANT MAIZE GENOTYPE AND CYTOPLASMIC POLYHEDROSIS-VIRUS ON GROWTH AND DEVELOPMENT OF THE CORN-EARWORM (LEPIDOPTERA, NOCTUIDAE)

The effects of a maize, Zea mays L., genotype, 'Zapalote Chico' 2451#(P)(C3), resistant to the corn earworm, Helicoverpa zea (Boddie), alone and in combination with cytoplasmic polyhedrosis virus (CPV) on the growth and development of corn earworm were investigated. Corn earworm fed 'Zapalote Chico' silks incorporated into a laboratory diet were significantly smaller, had higher mortality, and required longer to complete each developmental stage when compared to those on control diet. CPV significantly reduced corn earworm larval and adult weights, prolonged larval developmental period, and adversely affected percentages of pupation and adult emergence. 'Zapalote Chico' and CPV interacted synergistically with respect to pupal and adult weights and antagonistically with respect to larval weight. Nevertheless, adults from treatment combinations of CPV and silk weighed up to 41% less than those of control diet. 'Zapalote Chico' and CPV were independent in action with respect to percent larval survival, percent pupation and percent adult emergence of corn earworm. The effects of silk and CPV on developmental times were most severe for the larval stage. Larval period was prolonged 5.3 d when larvae were fed 'Zapalote Chico' alone; but, in combination with CPV (which increased larval period by 1.6 d), duration of larval stage was synergistically prolonged 10.8 d (mean larval period, 23.8 d) when compared to that of the control diet. Pupal period in the treatment with combined silk and CPV was 13.2 d, which was significantly longer than the 11.8 d on control diet. The mean developmental period from neonate to adult for corn earworm fed silk was 30.3 d; but it synergistically increased to 37.4 d when CPV was given together with 'Zapalote Chico', as compared to 24.8 d in the control. The potential use of maize resistance and CPV in the integrated pest management of corn earworm is discussed.