The predicted damage and yield loss under field conditions caused by rice leaffolder (Cnaphalocrocis medinalis) Guenee to the rice cultivar IR 50 was more in the unprotected crop than in protected crop. The yield loss was more when the infestation occurred at 40 days after sowing (DAS) than at 30,60 and 80 DAS. The damage and yield loss was not concomitant with the larval population. The economics of protection of grain crop showed that the protection was not necessary when the crop was infested at 30, 60 and 80 DAS while at 40 DAS the protection was necessary. A seed crop may warrant protection of the crop at both 30 and 40 DAS.

Results of field experiments revealed that three releases of biocontrol agents viz., Tricbogramma chilonis (1,00O,OOO/ha/release) and Brinckocbrysa scelestes (50,0OO/ha/release) on 90, 105 and 120 days after sowing could effectively check the population of Heliotbis armigera and Bemisia tabaci which was equal to that of insecticides. Two applications of nuclear polyhedrosis virus of Spodoptera litura at 250 larval equivalents (LE)/ha with adjuvants could effectively control S. litura larval population and damage. The seed cotton yield could also be increased in biocontrol plots which was equal to that of insecticide treated plots.I . T~-~chogrammu cbilonis (Ishii.) at 1,000,000 parasitoids/hdrelease, 2. Bririckocl~rysa ( C h r y s o p~) scelestes (Banks) grubs at 50,000/ha/rclcase, 3 . Spodopteru litura NPV at 250 LE with adjuvants crude sugar, 2.50 kg + cotton seed kernal powder (CSKP) 0.3 kg/ha. U.S.

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Two seasons experiments conducted for the evaluation of combined use of nuclear polyhedrosis viruses (NPVs) of Spodoptera litura (Fb.) and Heliothis armigera (Hb.) indicated that single application of NPVs each at 250 larval equivalents with crude sugar (jaggery/gur) 2.5 kg/ha was as effective as that of two aplications of chlorpyriphos 200 g ai/ha at 7 days interval in reducing the larval populations. The groundnut pod yield was also significantly increased over untreated check and was on par with chlorpyriphos treated plots. The cost benefit ratio was 1:3.97 in NPVs treatment against 1:3.83 in chemical insecticide treatment. Zusammenfassung Über eine kombinierte Anwendung von Kernpolyeder‐Viren gegen Spodoptera litura (Fb.) und Heliothis armigera (Hb.) an Erdnuß (Arachis hypogaea L.) Bei zweijährigen Experimenten über die Wirkung von Kernpolyeder‐Viren (NPV) gegen Spodoptera litura und Heliothis armigera wurde festgestellt, daß eine einmalige Applikation des Pathogens unter Verwendung von Rohzucker (2,5 kg/ha) als Träger etwa die gleiche Wirkung hatte wie 2 Applikationen mit Chlorpyriphos (200 g/ha). Die Erdnuß‐Ernte nach NPV‐Anwendung nahm ebenfalls zu und überstieg deutlich jene auf unbehandelten Feldern. Sie entsprach etwa der Ernte der mit Chlorpyriphos behandelten Felder. Die Kosten/Nutzen‐Relation war mit 1:3,97 (NPV) und 1:3,83 (Chlorpyriphos) nach beiden Behandlungen in etwa gleich.

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