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Abstract: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.

Papaya cubes at maturity stages, 5-45 % yellow (more green than yellow) and 55-80 % yellow (more yellow than green) were washed with 5 % H2O2, drained and packaged in PVC trays having five, seven and ten micro-perforations and stored for 19 days. PVC trays with 3 mm diameter punch holes were used as the control. Based on physico-chemical properties, optimum maturity for papaya and micro-perforation level of PVC trays were determined. Effectiveness of citric acid in prevention of browning was also tested. Firmness and TSS changed significantly, on day 19. O2, CO2 and C2H4 concentration changed 2.4 to 4.2 %, 23.4 to 5.9 %, and 0 to 0.13 % respectively, from day 3 to 19. pH and titratable acidity did not change significantly throughout the storage. Pretreated papaya cubes, packaged in PVC trays with ten micro-perforations, kept under 4 °C had storage lives of 19 days.

Rural agricultural sector in developing countries such as Sri Lanka is still lacking efficient and cost effective devices for processing of agricultural produce. A dual heat dryer which utilises rice husk and solar energy for thermal energy generation required for the drying process was designed and developed at the Institute of Post Harvest Technology (IPHT), Sri Lanka for dehydration of agricultural produce. Performance evaluation of the dual heat dryer gave promising results for adoption by the farming community. The dryer is able to generate drying air temperatures ranging from 40 to 110°C thus, facilitating a variety of crop produce to be dried, such as drumsticks, bitter gourd, papaya, mango, lemon grass, mushroom and many more, with natural convection airflow. In most instances drying using solar energy alone is insufficient to accomplish the drying operation because the drying process has to be continued up to 10-15 hrs extending into the night. The incorporation of biomass energy into solar drying enables the drying process to be continued even in the absence of sun shine and thereby ensuring product quality. The benefit/cost ratio is 10:1 in the dryer and hence adoption by the farming community or in rural areas is extremely feasible. Furthermore, the renewable energy technology discussed in this paper would help to enhance the socioeconomic development of the rural community in developing countries like Sri Lanka.

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