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Key factor responsible for fluctuations in rice yellow stemborer populations in deepwater rice ecosystems

Published online by Cambridge University Press:  19 September 2011

Zahirul Islam
Zahirul Islam
Affiliation:
Entomology Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh
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Abstract

A series of life tables (22 generations) for the rice yellow stem borer, Scirpophaga incertulas (Walker), a major pest of rice in Bangladesh, was constructed. In a deepwater rice ecosystem, the S. incertulas population dropped to a low level in the second or third generation (May-June), then reached the annual peak level in the fifth generation during September-October. The population dropped again to the lowest level in the sixth generation (November-February) when the larvae remained in diapause for about 3 months. In general, the population suffered very high mortality (99%). The estimated egg mortality was 49%; about 96% of the hatched larvae failed to penetrate into the rice stem; 39% larvae and 27% pupae died inside the stem. The population suffered very high mortality (96 %) at the early larval stage and the resultant survivorship curve was type III. Key factor analysis revealed that the disappearance of newly hatched larvae before penetration into the rice stem was the key mortality factor responsible for population fluctuations between generations. Disappearance of young larvae and egg mortality were density-dependent, but of a weak type.

Résumé

Une série de budgets vitaux (portant sur 22 générations) ont été construits pour le foreur de la tige de riz, Scirpophaga incertulas (Walker), un important ravageur du riz au Bangladesh. Dans un écosystéme de riz flottant, la population de S. incertulas a chuté à un bas niveau à la 2éme et 3éme génération (Mai-Juin), puis a atteint son pic annuel à la 5éme génération (September-Octobre) pour ensuite génération (Novembre-Fevrier), au moment où les larves entraient en diapause durant 3 mois environ. En général, la population a subi une trés forte mortality (99%). La mortalité au niveau des oeufs était estimee à 49%; environ 96% de larves écloses n'ont pas réussi à pénétrer dans la tige du riz; 39% de larves et 27% de pupes étaient mortes a I'interieur de la tige. La population a subi une trés forte mortalité à un stade larvaire précorce et la courbe de survie qui en a résulté était du type III. L'analyse du facteurolé a révélé que la disparition de larves nouvellement écloses avant leur penetration dans la tige, était principalement responsable des fluctuations des populations observées entre les générations. La disparition de jeunes larves et la mortalite au niveau des oeufs étaient dépendantes de la densité, mais leur cocours était faible.

Keywords

deepwater ricedensity-dependentkey factorlife tableScirpophaga incertulasyellow stemborerriz flottanteffet de la densitéfacteurolébudget vitalScirpophaga incertulasforeur de la tige
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 15 , Issue 4-5 , October 1994 , pp. 461 - 468
Copyright
Copyright © ICIPE 1994

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