author(s)
Chandan Maity, Palash Mondal and Laltu Mondal

abstract
Tomato, Lycopersicon esculentum is one of the most popular and widely grown vegetable in the world. In India, tomato is cultivated extensively in different parts of the country and considered one of the most remunerative vegetables. Among pest complex of tomato Helicoverpa armigera is an important pest which causes considerable losses in quantity of tomato fruits. Therefore to minimize the loss an experiment was conducted to study the biology of two generations of H. armigera in the laboratory of Department of Plant Protection, Palli Siksha Bhavana, Visva Bharati at 26±1 ºC and 80±5% RH. As these information will be helpful to formulate pest management strategies. The experimental findings on life tables of first and second generation indicated that age specific survival (lx) of insect was gradually decreased with the advancement of time. Expectancy of life also revealed similar trend in both generation. Results regarding the female fertility validates that immature stage including the pre reproductive period of H. armigera was 40.5 days in first and second generations. Thereafter, insects continued to lay eggs for 6 days and 7 days in first and second generation respectively. Natality rate (mx) i.e. the number of female off-spring produced/ female at age x in first and second generation were not similar during the whole length of reproductive period. The net reproductive rate (R0) of first generation of H. armigera was estimated 133.83 females/ female while mean length of generation (T) was 43.7 days. Whereas in second generation which was estimated 126.22 females/ female while mean length of generation (T) was 43.9 days. Where, the approximate rate of increase (rapprox) was slightly lesser than the actual rate of natural increase (raccurate) in both generation, which indicated the population trends towards overlapping generation. The finite rate of increase (λ) was 1.118 females/ female/day, potential fecundity (Pf) was 277.7 females/ female and monthly rate of increase (MRI) was 28.39 females/ female while time required for population to double (DT) was 6.18 days in first generation. While in second generation almost similar trends were observed, the finite rate of increase (λ) was 1.116 females/ female/day, potential fecundity (Pf) was 336.5 females/ female and monthly rate of increase (MRI) was 26.91 females/ female while doubling time (DT) was 6.28 days. The experimental findings revealed that that larval period of first generation of H. armigera was 22 days while pupal period and the adult longevity were 11 and 10 days, respectively. The above biological parameters indicated that the insect could complete a generation within almost one and half month. The results also revealed that per cent adult formation (47%) affected the growth index (1.42) and suitability index (0.05) of the insect. The reproductive period of the female insect was continued up to 6 days. Similarly, in second generation larval period of insect continued up to 23 days while pupal period lasted for 12 days and the adults lived up to 8 days. The per cent adult formation was 58%. The growth and suitability indices were 1.65 and 0.05, respectively. The reproductive period of the female insect continued up to 7 days.