Citation
Wessene, Mekasha Chichaybelu
(2004)
Utilization of Solar Heat for the Control of Cowpea Seed Beetle, Callosobruchus Macilatus (Fabricius) (Coleoptera : Bruchidae).
Doctoral thesis, Universiti Putra Malaysia.
Abstract
A survey, consisting of two hundred sample farmers, was conducted in major
cool-season food legume growing regions of Ethiopia. Assessment of grain
legume seeds collected from sample farmers' stores revealed the importance of
adzuki bean beetle, C. chinensis (L.). Storage pests were more serious in mid
altitude than highland areas. Farmers realized the negative effect of storage
insect pests on marketability, consumption quality and viability of legume seeds.
Hence, development of economically feasible and environmentally friendly
control options is needed.
Biology of C. maculatus was studied on adzuki bean seeds in Malaysia at UPM.
Mated female bruchid laid 61.8 eggs on average in its life with reproductive
effort of 11.6. Eggs had average incubation period of 4.6 days and mean
hatchability rate of 77.9%. Four larval instar stages were recognized. The insect
had mean developmental period of 27.8 days with adult emergence rate of
62.0%. Number of eggs had strong negative relation to age of female bruchid
while developmental period had positive relation.
Obtuse-base-angle box heaters glued from inside with aluminum foil had better
ability in trapping solar energy where 118' base-angle box had significantly high
performance. Square box heaters painted black from inside trapped higher
solar energy with better performance of boxes of 10 cm height, though not as
capable as the obtuse-base-angle box heaters. The different glazing
thicknesses and glazing layers did not show significant effect on the extent of
trapped energy. Box heater of 118' base angle, glued from inside with
aluminum foil was, therefore, promoted for further evaluation of the effect of
heating on C. maculatus, due to its better performance in trapping solar energy.
Effect of heat treatment on C. maculatus and adzuki bean seed moisture
content and germination was evaluated. Exposure of the various developmental
stages of C. maculatus to heat for up to 45 minutes raised the temperature
between and within the seeds well in excess of the lethal level and resulted in
complete control. Treatment of adzuki bean seeds with heat for up to one hour
did not significantly affect seed viability. Though there was no significant
difference, about 18.6% and 27% loss in seed viability resulted from seeds
treated for 30 and 60 minutes, respectively, should not be undermined. Hence,
adzuki bean seeds meant for planting should not be heat treated to control
storage insect pests. However, heat treatment had no much effect on seed
moisture content.
Assessment on the effect of seed layer thickness on the efficacy of heat
treatment against C. maculatus revealed that up to 3 cm thickness of adzuki
bean seed can be treated at a time, as neither adult bruchids survived heat
treatment nor emerged later. Therefore, solar heating of infested adzuki bean
seeds using the aforementioned box heater around noon for an hour can give
effective control of C. maculatus.
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