Control of insect pests under ware-house conditions using smoke generated from partial combustion of rice (paddy) husk

Adult Sitophilus oryzae and Rhyzopertha dominica , two major devastating insect pests of stored paddy in Sri Lanka, included in cloth sacks with rice medium inside were placed at three locations of the poly sack stacks containing paddy viz. outside, just inside and centremost. They were then exposed to smoke generated from partial combustion of paddy husk for 2 1/2-3 hours {where carbon monoxide (CO) concentration was higher than 5000ppm} and sealed for 18, 36, 54 and 72 hours in the first step and repeated for a similar time period with a subsequent smoking in between as against the control. Results revealed that increasing CO 2 concentrations in smoke caused no significant mortality on the target insects. Smoke generated by partial combustion of paddy husk where CO concentration was above 5000ppm was directly responsible for insect mortality. Insect mortality was increased with the increase in the sealed period up to 72 hours irrespective of both the location of insect (outside, just inside and centermost) and species. However, a significant difference in the mortality levels of insects was observed among the above 3 locations, outside the poly sack bag recording the highest mortality. This indicates that the poly propylene membrane acts as a physical barrier for the penetration of smoke into the poly sacks. Experiments under ware-house conditions also revealed that there was no significant difference among the treatments smoked once a week, once in two weeks and once a month in terms of percentage weight loss due to insect attack which all differed significantly with the control stack which was not smoked. This study shows the possibility of using smoke generated from partial combustion of paddy husk for the control of stored product insect pests as an alternative to the chemical insecticides.