Significance of the Larval Population Size of the Cereal Leafminer Syringopais temperatella Led. (Lepidoptera: Scythrididae) and the Diapausing Depth in the Soil on the Yield Variables of Wheat and Barley

The cereal leafminer, Syringopais temperatella Led. is one of the most serious insect pests of wheat and barley in the Near East countries and their neighboring. Deep ploughing has negative impacts on soil-inhabiting pests. Therefore, it was of vital important to know the soil depth at which the pest larvae diapause to determine the right ploughing depth to facilitate pest control. Soil samples were collected at four different soil depths from a highly infested field and these samples were used to plant wheat and barley seeds in pots. Results revealed that foliage infestation percentage and larval population size in plant leaves were higher on plants grown in soil taken from deeper soil depths than shallower ones. Barley yield in the control treatment was significantly higher than those in the four soil depths, while for wheat, there were no significant differences in the yield among the soil depths treatments including the control. There was a reduction in the grain yield and in the dry straw mass of plants that were planted in soils taken from deeper depths since they contain larger numbers of pest larvae which attacked plant leaves after getting out of dormancy. Results also showed that the leaf infestation percentage was positively correlated with the larval population size in the soil; meanwhile, the grain yield and the dry straw mass were negatively correlated with the larval population size.