Helicoverpa armigera causes economic damage to several crops and is a direct pest with high fecundity and multivoltine overlapping generations. Although, immense work has been done on H. armigera on several hosts but information on its demographics on apple is lacking. This study, therefore, presents the first report of its demography on apple. The study showed that the insect, completes its life cycle on immature fruit stages i.e. pea and walnut stages but not on mature fruits. In the present study, the incubation period of the test insect ranged from 2.8 to 3.6 days irrespective of the host. Similar observations were reported 13,14 with incubation period ranging from 3.11 to 3.6 days, respectively.
However, the present findings contradicted these reports which showed a shorter duration larval period with average duration of first, second, third, fourth and fifth instar larvae as 2.27±0.08, 2.42±0.08, 2.67±0.07, 2.83±0.07, 3.4±0.1 and 3.37±0.11, respectively. The larval development of H. armigera was completed with five instars which is similar to the results of studies conducted 15,16 but, in contrary to the earlier reports13,17,18 who reported six larval instars. The intraspecific variation in number of larval instars could be predisposed to changes in temperature, photoperiod, humidity or other external as well as genetic factors.19
The results of larval duration in the present study is partially in agreement with earlier studies where it was reported to be 2.4±0.52, 2.7±0.48, 3.8±0.42, 4.3±0.48 and 4.5±0.53 days20 and 2.5±0.52, 2.6±0.51, 3.6±0.51, 4.4±0.52 and 4.7±0.48 days, respectively.18 In the present study, the early larval instars took more time for completion than the previous reports, which could be attributed to variation in host on which the larvae were reared. Pupal period in the present study fluctuated between 10 and 11 days and was comparable to that reported 21 who recorded average pupal duration of 9.14 to 12 days. The experiment results also agree partially 15,20,22 who reported pupal period of 13.78, 13.8 and 12-15 days, respectively. Adult longevity in the present study varied from 6.5 to 7.5 days and is in partial agreement with results obtained from previous reports.20,23
The results of the present studies on duration of reproductive stages are in accordance 17 who reported the average adult pre oviposition period and oviposition period of H. armigera on pigeon pea to be 2.5 and 5 days, respectively. Similar results were recorded 20 who found the mean adult pre oviposition and oviposition period on chilli as 3.1±0.74 and 5.5±0.53 days, respectively. The study conducted 15 on tomato in semi-arid region of Rajasthan revealed analogous results with average pre-oviposition and oviposition periods ranging between 2.15-3.21 and 5.25-6.6 days, respectively.
Based on the findings of the present study, the intrinsic rate of increase (r) varied from 0.12 to 0.15 and the mean generation time (T) from 36.59 to 42.56 days which is similar to the results obtained 24 who found that these parameters of H. armigera as 0.1 females per female per day and 36.7 to 46.4 days, respectively. Comparable results were obtained 25 who reported the intrinsic rate of increase as 0.1 females per female per day, although, the true generation time was comparatively longer (48.59 days). The present results are also in conformity 26 who found the intrinsic rate of increase (r), finite rate of increase (λ) and true generation time (T) as 0.12, 1.12 and 43.9 days, respectively. The life fertility parameters of the present studies were comparable to those reported.27,28,23 However, the observations recorded 29 differed with lesser value for intrinsic rate of increase (0.76-0.94) and higher values of finite rate of increase (2.13-2.48) and true generation time (47-54.6 days) than those obtained in present studies.