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Distribution of larvae of Ophionea indica thunberg (Carabidae), a predator of the rice [Oryza sativa] gall midge, Orseolia oryzae (wood-mason) in paddy fields of Sri Lanka

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Kobayashi, M. (Chugoku National Agricultural Experiment Station, Fukuyama, Hiroshima (Japan))
Kudagamage, C.
Nugaliyadde, L.

Populations of Ophionea indica larvae inhabiting the gall cavities resulting from infestation with the rice gall midge, Orseolia oryzae were investigated in the paddy fields of Sri Lanka. The surveys were conducted three times from 1989 to 1992 during the Yala and Maha (monsoon seasons) and early Maha (dry season) seasons. In the Yala season, the population was high in the wet zone where a mean value of 3.0 larvae per 100 galls was observed, while only 0.6 larvae per 100 galls were recorded in the intermediate zone. In the maha season, the mean value of 0.6 larvae was recorded in the wet zone, 0.8 larvae in the intermediate zone and 0.2 larvae in the dry zone. In the dry season no larvae were detected. These results suggest that the population density of the predatory larvae is high in the wet zone in the monsoon seasons. The predators seemed to aggregate in the paddy fields where the rice gall midge pupae were abundant, because marked differences in larval catches were observed in the same district such as in the Gampaha district in the Yala season. It is assumed that the predator larvae may possibly detect the moving pupae in the gall by visual stimulus, because they bore a hole in the gall to penetrate into it to feed on prey pupae

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