Synergism of Entomopathogenic Organisms Associated with Zonocerus variegatus

Abstract

Aim: Entomopathogenic organisms were investigated for their lethal ability, minimum lethal concentration and synergy against caged short-horned grasshoppers (Zonocerus variegatus). Place and Duration of Study: Study was carried out in the Department of Biological Sciences, Wesley University, Ondo, Nigeria between March and August, 2016. Methodology: Adult Z. variegatus of both sexes were caught by sweep nets from the university cassava (Manihot esculenta) farm, divided into batches of 10, fed and observed for the onset of disease symptoms such as lethargy, colour change, abnormal outgrowths and death. Organisms were isolated from the diseased insects. Pathogenicity test was carried out on all the isolated organisms. Synergism was examined amongst the organisms by challenging the insects with more than one entomopathogens at the same time. Results: Duncan’s Multiple Range Test was used for the estimation of means. The ‘t’ value was tested at 95% confidence interval. 10 insects were included in each sample batch and each test were carried out in triplicates (n = 3), Bacillus subtilis, Beauvaria bassiana and Aspergillus niger were able to induce pathogenicity on the insects. B. bassiana caused death in 8.67±0.58 insects, A. niger was lethal on 7.33±0.58 while B. subtilis was lethal on 8.67±0.29. The minimum lethal concentration (MLC) of the organisms when used to challenge the insects are 5.0 ×104 spore forming units per milliliter (sfu/ml) for B. bassiana as it causes death in 6.33±0.58 out of the 10 insects used. 8.0 ×108 sfu/ml of A. niger causes death in 6.67±0.58 and 6.0 ×106 cfu/ml for B. subtilis. Synergistic test carried out shows greater entomopathogenic effect when a bacteria-fungi formulation was used compared to when a fungi-fungi formulation was used. ‘A. niger - B. bassiana’ formulation caused 5.33±0.58b death while the formulation using A. niger – B. subtilis and B. bassiana – B. subtilis caused 6.33±0.58c and 6.67±0.58cd lethal cases respectively. Conclusion: B. subtilis, B. bassiana and A. niger isolated from diseased Z. variegatus in this study possess entomopathogenic ability. They can be further studied for the enhancement of their entomopathogenicity, biosafety, most suitable method of delivery and mass production.