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Abundance of Heliothls Armlgera (Hubner) and Its Natural Enemies in Cotton lntercropped with Cereals or Legumes
Thesis Abstract:
The abundance of Heliothis armigera and its natural enemies on cotton, monocultured and intercropped variably with corn, sorghum, soybean, and peanut, was studied in the Central Experiment Station of the University of the Philippines Los Bafios during the 1988 dry and wet seasons.
The number of H. armigera eggs increased as the cotton plants reached flowering stage. A significantly lower number of eggs and larvae was observed in cotton intercropped with corn and sorghum than in monocultured cotton or intercropped with soybean or peanut at 77 days after planting (DAP).
H. armigera on squares, flowers. and bolls were generally lower in cotton intercropped with corn and sorghum than in other intercrops or monoculture. The highest yield of cotton was obtained from cotton intercropped with corn and peanut in the dry and wet seasons. respectively.
Aphis gossypii, Amrasca biguttula, and Anomis flava were the earliest insect pests recorded during both seasons. The population of cotton aphids, A. gossypii, was high at the early growth stages of cotton. As a major pest, the population of cotton leafhopper, A. biguttula, increased continuously as the cotton plant reached the flowering stage and balling formation in the dry and wet seasons, respectively. The highest populatio.n of semi looper, A. flava, was observed at 56 and 42 DAP in the dry and wet seasons, respectively. Nezara viridula and Dysdercus cingulatus were encountered at 56 DAP in the dry season while Sylepta derogata and Eariasfabia at 35 DAP in the wet season.
The first colonizer predators, Menochilus sexmaculatus and syrphid flies, were present from 28 to 42 DAP. The most abundant predator was Campylomma livida, whose population was high at squaring and boll formation in the dry and wet seasons, respectively. Other insect predators identified with considerable population were Metioche vittaticollis and Anaxipha longipennis, and spiders.
Two parasitoid species were found during the wet season: Trichogramma chilonis on eggs and tachinid flies on larvae. However, no parasitoids were found during the dry season. Percent parasitism was higher in cotton intercropped with corn and sorghum.
In the laboratory, Harmonia octomaculata was the most promising predator observed, having consumed the highest number of eggs and larvae. T. chilonis was so far the most effective egg parasitoid of H. armigera among the four Trichogramma species.