Abstract:

Among the storage problems of maize and beans, insect pests are a major constraint. In order to minimize storage losses, farmers usually apply different methods which include physical or inert materials, cultural means, botanical and chemicals to control storage pests. However, none of the individual control method has been successful. Diatomaceous earth (DE), a natural mineral product from fossilized silica shell or remains of unicellular organisms is reported to be effective on storage pests. Of recent, DE has been found in Nebbi district in Uganda. The efficacy of DE of Uganda origin is not well known. A study was therefore conducted to evaluate the effectiveness of DE of Uganda origin against S. zeamais and A. obtectus, the major storage pests of maize and beans respectively. binocular microscope. Three experiments were conducted; first was to determine the DE optimum dosage rate, the second one was to study the effect of DE on hatchability and survival of A. obtectus and third was to compare efficacy of DE, selected botanicals and pesticides against the two storage insect pests. Optimum DE application rate was determined by investigating six different dosage rates of 0.5,1,2,3,4 and 5% weight per weight basis. The control was untreated grain. The treated and non treated grains were artificially infested with 5 males and 10 females of each of the species obtained from routine stock culture, each treatment replicated four times. 2-3 days old A. obtectus and 14 days old S. zeamais were used. The insects were allowed to mate and oviposit for seven days and then removed and discarded. To count the eggs of S. zeamais, the grains were treated with acid fuschin to stain the eggs. For Acanthoscelides obtectus, eggs were separated from DE-bean mixture and counted under a After counting, the eggs together with the pre determined DE dosages and grains were put back to their respective containers and incubated. The infested cultures were placed in shelves in laboratory under prevailing ambient conditions until the F4 progeny started to emerge. The adults that emerged were counted daily, recorded and then discarded. Results showed that there were significant differences (P< 0.05) in number of eggs laid and adult emergents in grains treated with DE compared to the controls. The untreated grain registered the highest number of eggs laid and adult insect emergence while grains treated with DE at 5% dosage rate recorded the least number of eggs and insect emergence. However, there were no significant differences (P> 0.05) in the mean number of emergent adults in grains treated with DE at different dosage rates. The highest hatchability percentage and survival of A.obtectus was in the controls and lowest in grains treated with DE at 5% dosage level. The effect of botanicals, DE (0.5, 1, and 2%) and insecticides (actellic super1%, malathion 2% dust) were evaluated. Botanicals tested included; tobacco leaf and seed powder, neem leaf and seed powder. The same protocol used in experiment 1 was adopted. Neem leaf and tobacco seed powder were not toxic to S. zeamais and A. obtectus. Tobacco leaf and neem seed extracts were effective against the two candidate storage insect pests. The mean number of S. zeamais and A. obtectus emergence in maize and beans treated with DE at 2% and 1% respectively were not statistically different from those treated with synthetic pesticides. There were no significant differences (P< 0.05) in mean number of adult that emerged and seed damage in grains treated with DE, tobacco leaf and neem seed powder. The incorporation of DE in integrated pest management of S.zeamais and A.obtectus and their application on-farm is recommended. On-farm trials, should however, precede recommendation for wider use.