Appropriate dates of Trichogramma evanescens (west.) release to control rice stem borer, and effect of sprayed chemicals on parasitoid survival [electronic resource].

Includes reference.

A schedule was investigated to find out the most appropriate date (or dates) for releasing Trichogramma evanescens (West.) to control the rice stem borer, Chilo agamemnon Bles. in rice fields. Due to release, the average reductions in dead hearts were 54.11, 24.22 and 63.30 % with releases on 20 June, 5 July and 20 June + 5 July, respectively. The average reductions in white heads ranged from 28.35, to 81.67 % due to one, two or three releases. However, two releases on 5 July + 20 July or on 20 July + 5 August achieved a satisfactory borer control, resulting in 71.09 and 74.13 % reductions in white heads. In a large-scale experiment conducted in the farmers' fields (a total of 52 feddans at Dakahlia and Kafr EI-Sheikh Governorates), the reductions in dead hearts were 87.33 % due to the parasitoid release compared to 58.97 % due to insecticide application, while those of white heads were. 94.38 and 46.28 %, respectively. In a laboratory test, the chemicals (nutrients and fungicides), commonly used in rice cultivations, were found safe when sprayed onto the parasitoid cpnfined in Sitotroga cerealella (Oliv.) eggs (enveloped or nonenveloped). Only the insecticide, Malathion was toxic; 17.89 and 100 % parasitoid mortality for the enveloped and nonenveloped parasitoid, respectively. When the emerging parasitoid adults were exposed to the chemicals, or even to tap water, all the emerging individuals were killed. These findings show the importance of releasing the parasitoid twice from early July to early August, and to avoid spraying any chemicals onto the emerging T. evanescens adults. In all cases, the insecticide applications should be completely forbidden in the release fields.

Summary in arabic.

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