.

The ability of rice husk powder (RHP) and rice husk ash (RHA) to protect cowpea
seeds against Callosorbruchus maculatus Fabricius damage was investigated under controlled
temperature and relative humidity conditions. Lethality of RHP and RHA to adults and eggs of the
beetle was determined. Each product was further tested at 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 g/20 g of
grain respectively in glass Petri dishes against the beetle to determine prevention of seed weight
loss. Effect of temperature on use of relatively low doses of RHA was also determined. RHA caused
significant adult mortality at 0.5 g (100%) and 0.4 g (83.3%) within 1 day post treatment whereas
RHB caused 55% adult mortality at 7 days. Mean 2-day weight loss in adults exposed to RHA (2.40
mg) was significantly higher than for RHP (1.62 mg) and control (0.19 mg). RHA was significantly
lethal to C. maculatus egg and the lethality increased with age of egg. Female beetles laid
significantly fewer numbers of eggs on seeds treated with RHA than seeds treated with RHP and
the control, but F1 adult emergence from eggs laid was similar. There was no F1 adult mortality in
RHP treatments and the control but significant mortality occurred in RHA treatments. Seed weight
loss was significantly lowest when seeds were treated RHA ranging from 3.2% to 4.2%, but was
highest in seeds in the control (13.5%) and seeds protected with 0.1 and 0.2 g RHP (12.9%). When
applied at relatively low dosages, RHA was significantly more lethal to C. maculatus adults at 30°
C than at 25° C