Influence Of Tannic Acid On The Insecticidal Activity Of A Bacillus Thuringiensis Serovar Aizawai Formulation Against Spodoptera Litura Fabricius (Lepidoptera: Noctuidae)

We previously reported that tannic acid reduces the insecticidal activity of Bacillus thuringiensis serovar aizawai (Bta) against Spodoptera litura in a concentration-dependent manner. In this study, we further evaluated the biochemical mechanisms involved in the interactions between tannic acid and Bta. Application of tannic acid to the Bta insecticidal crystal protein (ICP) activated with trypsinization under alkaline conditions led to the formation of aggregates. Furthermore, the binding between the activated ICP and S. litura midgut brush border membrane vesicles (BBMVs) was evaluated in the presence of tannic acid. The binding of the activated ICPs to BBMVs decreased in a dose-dependent manner after treatment with tannic acid. As polyethylene glycol (PEG) forms strong bonds with tannic acid, its effect on the insecticidal activity of the Bta formulation was evaluated in S. litura third instar larvae. Although tannic acid reduced the insecticidal activity of Bta, the application of a Bta and PEG mixture improved the insecticidal activity, even in the presence of tannic acid. Tannic acid could also inhibit the growth of Bta in artificial media. Taken together, these results suggest that tannic acid inhibits the binding of ICP to BBMVs and the growth of Bta, which reduces its insecticidal activity.