Enhanced insecticidal activity through combination of two entomopathogens

The use of entomopathogens as biological control agents is well established, however sometimes it is desirable to enhance their insecticidal effects and reduce their disadvantages through the combination of other agents. The objective of this work was to prepare a combination of entomopathogens effective against two species of Spodoptera. Spodoptera exigua, and S. frugiperda neonate larvae were used in all bioassays. Bacillus thuringiensis HD-133 strain and two nucleopolyhedroviruses (SeMNPV and SfMNPV) were used. Bioassays to test LC₅₀ were conducted on artificial diet using 25 larvae for each bioassay with three replicates including a negative control. The LC₅₀ of the HD-133 and the SeMNPV was calculated for S. exigua, and the LC₅₀ of HD-133 and SfMNPV was calculated for S. frugiperda. The LC₅₀ was calculated for each entomopathogen individually and in combination. Results were submitted to Probit analysis, and mortality values were corrected with Abbott's formula. Results indicated that LC₅₀ calculated for S. exigua was: HD-133, 27µg/ml and SeMNPV 3.5x10² OB. The LC₅₀ calculated for S. frugiperda was: HD-133, 61.2µg/ml and SfMNPV, 4.9x10⁴ OB. Mortality percentages calculated individually for each entomopathogen were as follows: for S. frugiperda HD-133 = 44.30%, SfMNPV = 55.89%, and in combination (HD-133 + SfMNPV) = 88.23%. For S. frugiperda HD-133 = 43.63%, SfMNPV = 57.52%, and in combination (HD-133 + SfMNPV) = 98.52%. In this work, the combination of B. thuringiensis and a specific baculovirus have shown effectiveness through the combined use rather than individually as it can be seen in the mortality results.