A study was carried out to find out the effect of various weather parameters on the occurrence of major defoliators in soybean crop. Semilooper larval population was recorded late July/early August and their peak activity observed during 33-34, 33-36 and 37-39 standard weeks, in 2012, 2013 and 2014, respectively. Among the weather factors, morning relative humidity showed significant (r=0.954) and positively, highly influence on the larval population per mrl whereas evening humidity (r=-0.644) and sunshine hrs (r=-0.367) negatively and significantly influence the larval population per mrl. The various weather parameters significantly caused 92 per cent variations in larval population per mrl. The moth catches of Spodoptera litura increased from late-August to late-September and this trend was almost similar in different kharif seasons observed. Larval population of S. litura positively correlated with pheromone trap catches during 2014.

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The objective was to estimate avoidable losses due to defoliators in seed yield of soybean on four varieties viz., JS-335, JS-93-05, JS-95-60 and RKS-24.The semilooper population varied from 1.21 to 3.96 larvae/mrl on different soybean varieties. The maximum population was observed on JS-335 then JS-93-05 and JS-95-60 was significantly lower semilooper than that on RKS-24. Similarly, from the pooled data of three years, it is evident that the Spodoptera litura larval population varied from 1.54 to 4.77 larvae/mrl on different varieties of soybean. It was maximum on JS-335and minimum on JS-95-60 and JS-93-05. Under protected conditions, the minimal S. litura larval incidence of less than one larva/mrl was observed in all the soybean varieties. From the data it was evident that maximum yield loss in JS-335 during 2014 and 2016 corresponded with the maximum population of semilooper and S. litura larvae.

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