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Susceptibility of Six Varieties of Rice to the Infestation of Rice Weevil, Sitophilus Oryzae (l.) (coleoptera: Curculionidae)

HUMAYUN REZA KHAN
Department of Zoology, University of Dhaka, Dhaka‐1000, Bangladesh

POLASH KANTI HALDER
Department of Zoology, University of Dhaka, Dhaka‐1000, Bangladesh

Abstract/ Executive Summary:

The susceptibility of six varieties of rice, Oryza sativa, viz. Lata, Minicate, Nazersail, Parija, Kalijira and Kataribhog, to the infestation of the rice weevil, Sitophilus oryzae (L.), was studied on the basis of population build up under an ambient condition (28 ± 4ºC and 70 ± 4 % RH) of the laboratory. The mean weights of each grain of the above six rice varieties were 16.9, 16.1, 11.43, 13.87, 6.23 and 9.77 mg, respectively; mean lengths were 6.47, 6.56, 5.37, 5.38, 4.22 and 4.92 mm, respectively; mean widths were 2.45, 2.03, 2.05, 2.17, 1.6 and 1.9 mm, respectively; and moisture contents were 11.55, 10.75, 11.6, 12.71, 11.85, and 12.1 per cents, respectively. As far as the number of emerging adults is concerned, the weevil showed the highest number (695) in Nazersail on the 16th week, Lata (755) on the 18th week, Minicate (654) on the 16th week, Parija (482) on the 20th week, Kalijira (402) on the 20th week, and Kataribhog (456) on the 20th week. The mean numbers of the adult weevils in the above six varieties after 22 weeks of rearing were 425, 410, 351, 387, 357 and 400, respectively and was statistically significant at 5% level. The degree of susceptibility of the rice varieties to the rice weevils from the highest to lowest susceptibility was ? Lata > Nazersail > Minicate > Pariza > Kataribhog > Kalijira.

Keywords: Rice varieties, Weevil, Sitophilus oryzae, Susceptibility, Infestation

Location: Jagannath Hall of the University of Dhaka

Start Date: 00-00-2012

End Date: 00-00-2012

Program Area: Pest Management

Commodity: Rice

Objectives:

1. The present study was, therefore, undertaken to look into the nature of infestation of six rice varieties by the rice weevil, S. oryzae and to observe its population development on these varieties.

Methodology:

Six varieties of rice (Oryza sativa), studied were Najersail (parboiled), Lata (parboiled), Kalijira (un?parboiled), Pariza (parboiled), Minicate (parboiled) and Kataribhog (un?parboiled). The susceptibility of these varieties of rice to the infestation of the rice weevil, S. oryzae was studied in the Entomology laboratory of the Department of Zoology, University of Dhaka, at an ambient environment (28 ± 4ºC and 70 ± 4% RH) in the laboratory. The rice varieties were collected from some rice?stores of Dhaka city. The rice weevils (S. oryzae) were collected from the stored rice of the dinning mess of the Jagannath Hall of the University of Dhaka. The weevils were identified. Only fresh whole rice grains were selected; cracked or damaged rice grains were removed from the test samples. Any extraneous materials, when found, were also removed. Three rice grains from each of the varieties were randomly selected and their lengths, widths and weights were recorded. The grains were weighed with the help of an electric balance [Model: Scientech SA 210 (210 × 0.0001 G)]. The rice grain samples were disinfested by keeping them inside a deep fridge for one week and the grains were considered to be totally disinfested. After the treatment, the rice grains were spread on normal white papers at room temperature and humidity for 24 hours to bring them into normal condition. The moisture content of each rice variety was determined following the oven method. For this, 100 g of grains were taken from each variety and weighed. These were then kept in an oven at 60ºC for 24 hrs and after that the samples were weighed and recorded. The weight loss is considered to be equivalent to the moisture content of the rice grain. The per cent weight loss was calculated by the following formula: Weight loss (%) = [(X₁ – X₂)/X₁] × 100 where, X₁ = Initial weight of each grain sample; X₂ = Weight of the sample after heat treatment. The treatments were replicated thrice for each variety of the rice grain. For this experiment, 25 g of whole rice grains (not cracked or broken) from each rice variety were accurately weighed with a Triple Bean Balance and kept in plastic containers measuring 8 × 6 cm each. Five pairs of the newly emerged adults of 24?48 hours age group in the ratio of 1 : 1 were released into each container. Four replications were taken for each rice variety. The opening end of the container was covered with a piece of “Markin” cloth (for aeration) and tied with rubber bands. The containers were kept under the condition of normal room temperature and relative humidity for six months. The released weevils were allowed to remain undisturbed in the containers with the gains for the first four weeks. The first census of the weevils, both living and dead, was made after 30 days since the insect release, and subsequently at every 15 days of interval. After each count, the dead weevils were discarded and the living ones were returned to the rearing medium. The recording of the number of weevils continued up to 154 days. The data were analyzed statistically.

Source of Information: Dhaka Univ. J. Biol. Sci. 21(2): 163-168, 2012 (July)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

In conclusion, it might be said that the susceptibility of rice varieties to insect pest is a complex phenomenon. The study also shows that the susceptibility of six rice varieties to the infestation of S. oryzae depends not only on a single factor; but, it depends on the combination of many factors like grain hardness, nutritive value, and natural resistance. In addition, the factors comprising grain size and moisture content in the rice grains might be the reasons of severe infestation by the rice weevil population.

Knowledge Management: Journal