Biopesticide synergy when combining plant flavonoids and entomopathogenic baculovirus

William T Hay,Andie C Miller,Gordon W Selling,Robert W Behle,Mark A Berhow

doi:10.1038/s41598-020-63746-6

Abstract

Four crop plants known to be hosts for the lepidopteran Trichoplusia ni (soybean, green bean, cotton, and cabbage) were treated with the biopesticide AfMNPV baculovirus in a dosage response assay. Treated soybean had, on average, a 6-fold increase in virus activity compared with the other crops. Leaf trichomes on soybeans were not found to be responsible for the observed increase of insecticidal activity. Three flavonoid compounds (daidzein, genistein, and kaempferol) were uniquely found only in the soybean crop, and were not detected in cotton, cabbage, or green bean plant matter. The individual flavonoid compounds did not cause T ni. mortality in no-virus assays when incorporated into artificial insect diet. The combination of the three flavonoid compounds at leaf level concentrations significantly increased baculovirus activity in diet incorporation assays. When the daidzein, genistein, and kaempferol were added to artificial diet, at 3.5–6.5 × leaf level concentrations, virus activity increased 1.5, 2.3, and 4.2-fold for each respective flavonoid. The soybean flavonoid compounds were found to synergistically improve baculovirus activity against T. ni.

Highlights

While the chemical differences between the plant species are likely to be extremely numerous, we focused on identifying significant differences in leaf phenolic composition as these are known to be produced as plant defense compounds
AfMNPV treated soybean had, on average, a 6-fold increase in virus activity compared with the other crops
For T. ni, it had been previously observed that the presence of trichomes on soybean leaves decreased feeding and increased mortality with trichome density; the removal of the trichomes on the youngest fully expanded leaves resulted in a significant increase in T. ni feeding[22]

Summary

Introduction

This experiment was conducted to evaluate the impact of leaf pubescence on the activity of the virus treatments applied to soybean plants by comparing shaved with un-shaved plants. Artificial insect diet treatments containing genistein, daidzein and kaempferol were prepared to compare the effect of three flavonoids identified above on the insecticidal activity of the baculovirus. Kaempferol, daidzein, and a mixture of the three flavonoids (along with the DMSO and no-additive controls) were surface treated with 5 concentrations of baculovirus.

Results

Conclusion