Investigating the Effects of Host Grains on the Rice Weevil, Sitophilus oryzae (L.)

The present study was conducted to observe the effect of host preference on ovipsition, adult
emergence, adult body length, longevity and sex ratio of Sitophilus oryzae, the most cosmopolitan
pest which causes severe losses in rice, maize, barley, wheat. Investigation was carried out on
development of S. oryzae on four main cereal crops maize, rice, chick pea, and millet, under
laboratory conditions. The mean developmental period from egg to adult varied, being lowest on
maize (32.5 days) and highest on millet (43 days). The body length of the male and female were also
differing in the test grains. Overall the females’ body lengths were found to be longer than males in all
the test grains. The fecundity and longevity were also altered with the different grains. The highest
fecundity and longevity were found in maize with 453 adults in the lifespan of 184 days. With respect
to fecundity the female: male ratio was not found to be significantly differed in maize, rice and millet
(maize- 2.36:1, rice- 2.35:1 and millet- 2.21:1) while in chick pea a significant decrease i.e. 1.98:1
were observed. From the present study it was found that there was a linear relationship and a
significant correlation between grain loss and the number of adult emergence. All the stages of the life
cycle, starting form egg laying to the emergence were found to be highest in the maize. The study
also suggests that maize was rich in carbohydrate that has increased the size, fecundity and longevity
of the insects. Hence, maize is the best suitable grain for rearing of S. oryzae insects.