A thesis submitted in partial fulfilment of the requirement for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1995

A study was conducted on controlling insects of stored paddy with two biopesticides namely Neem oil and Bacillus thuringiensis (B.t.) from February to May 1995. One year old infested and freshly harvested aromatic rough rice variety Jasmine (Khao Dawk Mali 105) were taken for this study. Paddy after being treated with biopesticides were filled in the jute bags and stored in warehouse under natural condition. Seed viability, milling quality, moisture content, bulk density, weight loss, infestation rate were determined. Insect identification and quantification were done at three different doses of biopesticides. The doses were 10, 15 and 20 cc neem oil and 20, 30 and 40 cc of Bacillus thuringiensis per kg of paddy. Insects Rhyzopertha dominica Fabr. (Lesser grain borer), Sitophilus oryzae Linn. (Rice weevil), Sitotroga cerealella Oliv (Angoumois grain moth) and Tribolium castaneum Herbst. (Rust red flour beetle or Bran bug) were found to infest the stored paddy. The population of R. dominica was the highest in the controlled (96/kg) and B. t. treated (70/kg) fresh paddy in April and 34/kg in control and 18/kg in B. t. treated infested paddy. The population of Sitophilous and Tribolium were the second highest in fresh and infested paddy respectively during the same storage period. The bulk density of both fresh and infested seed was gradually decreasing as the storage duration increased except during the first month due to application of biopesticides. For the same reason the moisture content of fresh and infested paddy fluctuated with storage time. However highest weight loss was found in control (4.56 %) and B.t (4.75 %) treated fresh paddy. In case of fresh seed, germination rate initially was 95 percent and after three months of storage it was 96, 93 and 94 in control, neem and B.t. treated paddy respectively. The germination rate of infested seed was 75 % in February but in May it dropped down to 13 in control 26 in neem and 28 in B.t. treated paddy respectively. Milled rice and head rice percentage were found to be increasing in all neem and B. t. treated fresh paddy but in case of infested paddy, it was slightly decreased. No significant difference in whiteness was observed except control and Bi in infested paddy after 90 days of storage. Based on the three months paddy storage study with the application of neem oil and B. t., it is evident that if farmer use minimum dose (10cc/kg) of neem oil they can save paddy from insect attack and weight loss of paddy resulting in economic benefit.