ASSESSMENT OF THE LETHAL EFFECT AND BIOSAFETY OF ENTOMOPATHOGENIC MICROORGANISMS ASSOCIATED WITH ZONOCERUS VARIEGATUS AND MACROTERMES BELLICOSUS

Abstract

Entomopathogenic microorganisms isolated from diseased insects (Macrotermes bellicosus and Zonocerus variegatus) were investigated for their lethal effect. LD50 of each entomopathogen was determined. The ability of the entomopathogenic microorganisms to work in synergy was evaluated. Comparative assessment of the lethality between indigenous and imported strains of the entomopathogenic microorganisms was evaluated. The susceptibility of the entomopathogens to commercial antibiotics and extracts of Cola nitida and Terminalia schimperiana was determined. Mass production of the entomopathogens using organic byproducts was carried out. Toxic effects of the entomopathogens on experimental animals were carried out. Adult Z. variegatus and M. bellicosus were sourced from the university farm and termite traps respectively, allowed to acclimatize and observed for the onset of disease symptoms. Microorganisms were isolated from the diseased insects and subjected to pathogenicity test. Synergism was examined amongst the entomopathogens by challenging the insects with more than one entomopathogens. Antibiotic susceptibility test was carried out using disc diffusion method. Susceptibility of the entomopathogens to water extracts of T. schimperiana and ethanolic extracts of C. nitida was determined using the agar well diffusion method. Phytochemical analysis was done on both extracts. Mass production was done by growing the organisms on selected organic byproducts. Biosafety was determined by evaluating the toxic effects of the organisms on experimental animals. Results were subjected to statistical analysis using Duncan’s Multiple Range Test for the estimation of means. Results showed that Bacillus subtilis, Beauvaria bassiana and Aspergillus niger were able to induce pathogenicity on Z. variegatus while Metarhizium anisopliae, Pseudomonas aeruginosa and Serratia marcescens were able to cause disease in termites. The minimum lethal concentration (MLC) of the organisms required to induce pathogenicity in Z. variegatus are 5.0 ×104sfu/ml, 8.0×108sfu/ml and 6.0×106cfu/ml respectively for B. bassiana, A. niger and B. subtilis. For M. bellicosus, the minimum lethal concentration required for pathogenicity were 5.0×105sfu/ml, 8.0×107cfu/ml and 7.0×106cfu/ml for M. anisopliae, P. aeruginosa and S. marcescens respectively. Synergistic test carried out shows greater entomopathogenic effect when a bacteria-fungi formulation was used compared to when a fungi-fungi formulation was used. Comparative assessment between indigenous and imported strains showed that the imported strain of B. bassiana was more lethal on the Z. variegatus while the indigenous was more potent in other cases. Antimicrobial test done on the plant extracts showed that B. subtilis and S. marcescens are susceptible to Cola nitida and T. schimperiana while P. aeruginosa was resistant at most concentrations used. Phytochemical studies revealed the presence of glycosides, flavonoids, saponins and tannins in both extracts while anthraquinones and cardiac glycoside are absent. Tests on the conventional antibiotics showed that all the organisms are susceptible to gentamycin while P. aeruginosa was resistant to most antibiotics used. Mass production showed that A. niger had the best growth on all the substrates while M. anisopliae had the least growth. Histopathological analysis showed a mild congestion of coronary blood vessels of the heart harvested from rats infected with A. niger. There was severe degeneration of the epithelial cells on skins infected with P. aeruginosa. Rats infected with A. niger showed decrease in the amounts of Progesterone, Testosterone, Luteinizing and Follicle Stimulating Hormone. B. subtilis, B. bassiana and M. anisopliae showed the highest lethal activity on the insects of study. They also had the least toxic effects on the blood, hormones and organs of experimental animals. They can be used for the manufacture of biopesticides and further studied for the enhancement of their entomopathogenicity and mass production.