Biometric studies of rice weevil, Sitophilus oryzae (Linnaeus) (Coleoptera: Curculionidae) on stored rice grains

The biology and morphometrics of Sitophilus oryzae on rice variety 'Sonam' revealed that the S. oryzae completed its life cycle in four distinct stages viz., egg, larva, pupa, and adult. The observed fecundity of female was 231.00 ± 3.09 eggs with an incubation period of 5.76 ± 0.09 days. The larval period was completed in 26.88 ± 0.08 days with four instars under laboratory conditions. The larval duration was 4.88 ± 0.04 (1st instar), 5.72 ± 0.08 (2nd instar), 8.70 ± 0.10 (3rd instar) and 7.58 ± 0.04 (4th instar) days and the pupal period was 7.62 ± 0.08 days. Adult male lived for 60.18 ± 0.82 days while female for 76.94 ± 0.50 days. The pre-oviposition, oviposition and post-oviposition period was 4.80 ± 0.07 days, 55.82 ± 0.53 days and 19.52 ± 0.39 days, respectively. The entire life cycle of male and female was completed in 100.44 ± 0.85 days and 119.90 ± 0.44 days, respectively. Sex ratio (male to female ratio) was recorded 1:1.42. The morphometrics (length × width) of the larval instars 1^st to 4^th instars were 0.58 × 0.41, 0.90 × 0.52, 1.23 × 1.04 and 2.12 × 1.58 mm, pupa (2.41 × 1.61 mm), adult male (2.59 × 0.78 mm) and adult female (3.01 × 0.84 mm).