*Corresponding author's E-mail: kamlpau@gmail.com
Studies on biology of cabbage head borer, Hellula undalis, revealed that egg incubation period was 2.3 ± 0.48 days, and its length and breadth were 0.43 ± 0.01 mm and 0.31 ± 0.01 mm, respectively. The duration of 1st, 2nd, 3rd and 4th larval instar was 3.5 ± 0.48, 5.0 ± 0.82, 5.7 ± 0.48 and 6.3 ± 0.68 days, respectively. The total larval duration prepupal and pupal periods were: 19.3 ± 2.2 days, 2.7 ± 0.82 days and 12.7 ± 0.82 days respectively. The full grown larvae measured 22.09 ± 0.71 mm in length and 4.32 ± 0.46 mm in breadth. The adult longevity in case of male was 3.8 ± 1.0 days and of female was 5.7 ± 1.3 days, while pre-oviposition, oviposition and post-oviposition periods were 1.8 ± 0.42, 3.7 ± 0.63 and 1.2 ± 0.38 days, respectively. The wing expanse of male and female was 24.55 ± 0.78 and 21.35 ± 0.48 mm, respectively. The average fecundity was 147.9 ± 35 eggs/female.
