Department of Entomology, Himachal Pradesh Krishi Vishvavidyalaya, Palampur-176 062, District Kangra, Himachal Pradesh (India).
*Present address: Agriculture Development Officer, Biological Laboratory, Holta, Palampur-176 061, Distt. Kangra, H.P.(India).
The endopara sitoid, Diaeretiella rapae (M'Intosh), parasitised all the three aphid species viz, Lipaphis erysimi Kalt., Brevicoryne brassicae Linn. and Myzus persicae Sulz. In the field under nylon netting, maximum parasitisation of 21.05, 23.16 and 6.53 per cent in 1992–93; and 62.71, 55.67 and 17.18 per cent during 1993–94, was recorded on L. erysimi, B. brassicae and M. persicae, respectively. The parasitoid host ratio under nylon netting in the field varied from 1:4.75 to 1:38.30 (L. erysimi), 1:3.97 to 1:16.25 (B. brassicae) and 1:15.30 to 1:48.0 (M. persicae) during 1992–93; and 1:1.59 to 1:56.0 (L. erysimi), 1:1.79 to 1:23.05 (B. brassicae) and 15.28 to 1:16.0 (M. persicae) in 1993–94. The natural parasitisation by P. rapae in the field varied from 7.19 to 31.69 per cent (L. erysimi), 9.34 to 29.89 per cent (B. brassicae) and 3.70 per cent (M. persicae) in 1992–93; and 4.06 to 52.86 per cent (L. erysimi), 2.85 to 30.74 per cent (B. brassicae) and 1.33 per cent (M. persicae) in 1993–94. Peak parasitisation of 31.69, 29.89 per cent was recorded in L. erysimi and B. brassicae in the first week of March, 1993; while 52.86 and 30.74 per cent parasitisation in L. erysimi and B. brassicae occurred in the second week of March, 1994. During both the years, peak parasitisation by D. rapae was observed in the first fortnight of March. The parasitoid commenced activity from the first week of February to first week of April when mean maximum and minimum temperatures varied from 14.3 to 25.0S°C and 5.1 to 14.3°C, respectively. The other abiotic factors pertain to relative humidity 26 to 60 per cent, total rainfall 174.4 mm, wind velocity 6.0 to 7.9 km/hr, and sunshine 4.7 to 9.2 per day.
