In experiments to find the yield loss in soyabean due to the leaf miner, Aproaerema modicella (Deventer) and estimate the economic injury level (EIL), plants were infested at 30 and 45 days after sowing (DAS) with a fixed number of laboratory reared second instar larvae.
Grain yield was not reduced by one larva per plant at both 30 and 45 DAS, but the yield reduction which ranged from 2.7 to 6.1% was significant with two larvae per plant at both the ages. With an increase in larval population, there was a corresponding decrease in yield to the extent of 40% and 66% with 10 larvae/plant at 30 and 45 DAS respectively.
The regression of yield of leaf miner infestation indicated that yield was reduced by 0.463 and 0.716 g per plant for every larva per plant at 30 and 45 DAS respectively. Yield loss was greater in plants infested at 45 DAS than at 30 DAS with all populations tested.
The estimated economic injury level for A. modicella is 0.6 larva/plant at 30 DAS, and 0.2 larva/plant at 45 DAS. The suggested economic threshold level in soyabean of 85–90 days duration is 0.5 larva/plant (1 larva/2 plants) at 30 DAS and 0.2 larva/plant (1 larva/5 plants) at 45 DAS.