author(s)
Matangi Mishra and U Mukherjee

abstract
Pusa Mustard -25 was sown as test crop. Sowing of crop was done on November 30^th for two experimental years namely: 2017-18 and 2018-19. The incidence of Lipaphis erysimi Kalt. on mustard started from fourth standard week in both the years i.e. 2017-18 and 2018-19 at Tirhut College of Agriculture Dholi, Muzaffarpur. The incidence of mustard aphid started from fourth standard week during both the experimental years (2017-18 & 2018-19). Initially Lipaphis erysimi Kalt. was less in number (8.2 in2017-18 and 7.2 in 2018-19) but gradually the insect population started increasing very fast. Mustard aphid population attained its peak (222.4) during tenth standard week in the first year of experiment (2017-18) and became highest (208.8) during nineth standard week in the year 2018-19. The insect started decreasing from twelfth standard week and vanished in the thirteenth standard week. During 2017-18 the relative humidity at 1400 hr was negatively correlated while the maximum temperature and number of rainy days were negatively correlated in the second experimental year (2018-19). The rainfall has not any significant role in incidence of mustard aphid.