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.

Studies on losses in yield of rapeseed, Brassica campestris cv. Brown Sarson, caused by the mustard aphid, Lipaphis erysimi (Kalt.) were conducted under natural and artificial conditions. Based on the experiments on the influence of aphid exposure to the crop on aphid number and seed yield and the effect of varied aphid population at flowering/pod initiation stage and artificial release of aphids at 10-day intervals starting from 40 days of sowing on the plant height, number of siliquae per plant, number of primary branches, seed yield per plant and 1000-grain weight, a positive correlation between length of aphid exposure to the crop and aphid population was found. A negative relationship between aphid population, length of aphid exposure and seed yield was observed. An inverse and significant relationship existed between parameters contributing to yield loss and losses in seed yield. However, this relationship was not significant in siliquae per plant and 1000-grain weight. A similar relationship was observed in artificial infestation.

Effects of topical application of two juvenile hormone analogues (JHAs), R-20458 (6, 7-epoxy-1(p-ethylphenoxy)-3, 7-dimethyl-2-octene) and ZR-512 (ethyl 3, 7, 11-trimetnyl-2, 4-dodecadienoate) on reproduction and longevity of mustard aphid, Lipaphis erysimi (Kalt.) were investigated. Doses of the JHAs as high as 2 μg per aphid failed to reduce the fecundity of the aphid though initial reduction in the daily reproduction was observed. Also, the doses which induced morphogenetic abnormalities at the third-instar, could not affect embryogenesis.

The development of phase phenism in L. erysimi involved function related changes in the activity of hydrolytic enzymes. The esterase activity decreased from first to third instar and then increased in the fourth instar and adults. The decrease in the third and the increase from fourth instar up to adults was more in alatae than apterae. The acid phosphatase activity was maximum in second instar. It decreased in the third and then increased again in the fourth instar and adults. The increase was more in alatae than in apterae. The alkaline phosphatase showed a similar trend but was in contrast to acid phosphatase and showed low activity in alatae as compared to apterae.

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.