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Observations on the armyworm Spodoptera mauritia acronyctoides Gn. (Lep., Noctuidae) in Sarawak (Malaysian Borneo)
Published online by Cambridge University Press: 10 July 2009
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Observations were made on the bionomics of Spodoptera mauritia acronyctoides Gn. in Malaysian Borneo (Sarawak) during an outbreak in 1967. The outbreak was discontinuous over about 6 000 sq. miles, affecting 25 000 acres of lowland and upland rice. In the insectary the durations of the various stages were: egg 2·9 days, first- to seventh-instar larvae respectively 3·1, 1·8, 2·2, 2·1, 2·2, 2·3 and 4·9 days, and pupa 8·4 days. Larval instars could usually be distinguished on head width and the width of the faecal pellets. Food consumption of the larvae was greatest during the final instar. During the outbreak the larvae were found mainly on young rice, and also on young maize; wild host-plants included grasses and sedges, but dicotyledonous plants were not attacked.
Females generally mated on the night following emergence, and the pre-oviposition period averaged 2·9 days. Fertilised females laid an average of 1 749 eggs, 80% of the potential total. Virgin females laid only 22% of the potential, and resorbed some of their oocytes. The mean longevity of fertilised females was 5·5 days. Fecundity was directly correlated with pupal weight or length, and the weights of pupae produced in wet-rice fields were significantly heavier than those from dry hill-rice sites. There was a significant correlation between the weight of frass produced (hence food consumed) by the seventh-instar larva and the weight of the pupal stage. Pupae from larvae in crowded cultures were significantly lighter than those reared singly.
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- Copyright © Cambridge University Press 1969
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