The economic injury levels (EIL) of the mustard aphid, Lipaphis erysimi on mustard, Brassica juncea were evaluated in field trials in Tarai, India, during the winters of 1986/87 and 1987/88. The EIL values ranged between 37 and 4, and 48 and 6 aphids per 10 cm terminal shoot per plant during the 1986/87 and 1987/88 trials respectively. A one-day increase in crop exposure to the aphids led to a significant reduction in seed yield per plant, 1000-seed weight, number of siliquae per plant and number of seeds per siliqua. The highest benefit-to-cost ratio was obtained at 3 weeks of exposure, when initiation of insecticide application was most economical.

Polyphenism is a common feature in the mustard aphid, Lipaphis erysimi (Kalt.) in tropical countries. The function related changes in basic biochemical pool are reported during development of polyphenic forms. A gradual decrease in the protein content in this aphid was recorded, as the nymphs advanced in their instar number and reached adult stage. However, the protein content was significantly lower in the apterous forms as compared to alate. The number, density and mobility of protein bands varied as the nymphs passed through different instars and the number of bands was more in alate forms. The glycogen and trehalose contents showed a decrease upto the third instar and showed an increase in the fourth instar, but again declined in the adults of both the phases.