Assessment of bio-formulations of indigenous strains of Bacillus thuringiensis, Metarhizium robertsii and Metarhizium majus for management of the rhinoceros beetle, Oryctes rhinoceros L., in field

BackgroundAmong all the coconut pests, rhinoceros beetle causes acute and serious damage to coconut palm. Management of this pest is very difficult due to its nocturnal activity, and also, it damages the emerging leaf inside the bud. Management of rhinoceros beetle using entomopathogens will be of great importance as it is economical and ecofriendly. Studies were carried out to decipher the biocontrol potential of indigenous entomopathogenic bacterium (Bacillus thuringiensis) and entomopathogenic fungi (Metarhizium robertsii and M. majus) against Oryctes rhinoceros in the field, individually as well as in combination, by soil drench as well as by topical spray method.ResultsThe study showed that B. thuringiensis strain NBAIR-BTAN4 showed 24.8% mortality at 5th week in soil drench method and 24% mortality in topical spray method. M. robertsii showed 24% mortality at 5th week in soil drench method as well as topical spray method. Similarly, M. majus showed 24% mortality in soil drench method and 23.2% in topical spray method at 5th week. In combination, NBAIR-BTAN4 + M. robertsii showed 40.8 and 44% in soil drench and topical spray method at 5th week, respectively. Combination of NBAIR-BTAN4 + M. majus showed 44.8 and 40.8% in soil drench and topical spray method at 5th week, respectively. Combination of NBAIR-BTAN4 + M. robertsii + M. majus showed 52.8 and 57.6% mortality at 5th week in soil drench and topical spray method, respectively.ConclusionThe present study showed application B. thuringiensis in combination with M. robertsii and M. majus is effective in management rhinoceros beetle in coconut orchard. Study also indicated that soil drench method is more promising strategy than topical spray method in managing larval population of the beetles and also confirmed that B. thuringiensis, M. robertsii and M. majus are compatible and they seemed to have a synergistic effect in controlling the pest in coconut orchard.

Automated summary

The study showed that the combination of Bacillus thuringiensis with Metarhizium robertsii and M. majus is effective in managing the rhinoceros beetle in coconut orchards. The soil drench method is more effective than the topical spray method in controlling the beetles' larval population. The study also confirmed that B. thuringiensis, M. robertsii, and M. majus are compatible and have a synergistic effect.