Field density and biology of diamond back moth, Plutella xylostella L-(Lepidoptera: Plutellidae) on cauliflower in Manipur

The field density of Plutella xylostella L. was assessed over a period of two cropping seasons from January to April during 1994 and 1995 and it indicated that the maximum abundance was found during March. The field population of the larvae were correlated with ambient temperature, R H. and rainfall in order to study the effect of the latter on insect density. Studies on biology of P xylostella carried out at the laboratory condition of 23 +/- 1 degrees C and 45 +/- 2% RH. revealed that the period of incubation and larval development, the duration for the development of prepupae and pupa and adult longevity were found to be 2.18 +/- 0.12, 10.5 +/- 0.32, 1.6 +/- 0.15, 6.86 +/- 0.24 and 16.7 +/- 2.95 days, respectively. The larval stage consisted of four instars and each instar could be distinguished on the basis of body size. The mean fecundity was 153 eggs per female.