Toxicity and disruption of midgut physiology in larvae of the European corn borer, Ostrinia nubilalis, by anion transporter blockers

Abstract

In this study, four blockers of anion transporters (ATs) belonging to four different classes of organic acids, including DIDS (4, 4'-diisothiocyanatostilbene-2, 2'- disulfonic acid; a stilbene disulfonic acid), NPPB [(5-nitro-2-(3-phenylpropylamino) benzoic acid; an anthranilic acid)], 9-AC (anthracene-9-carboxylic acid; an aromatic carboxylic acid), and IAA-94 (indanyloxy acetic acid; an indanyloxy alkanoic acid), were tested for their toxicity against the European corn borer (ECB), Ostrinia nubilalis. All the AT blockers inhibited the growth of larvae, increased the developmental time, and decreased survival compared to controls, when second-instar ECB larvae were fed for seven days on treated diet. In general, DIDS and NPPB were the most active compounds, with the rank order of activity being DIDS>NPPB>IAA-94>9-AC. All the AT blockers decreased the midgut alkalinity in fifth-instar larvae when fed for 3 h on treated diet. Effective concentrations required for 50% decrease in midgut alkalinity (EC(50)) ranged between 29.1 and 41.2 ppm and the rank order of activity was NPPB>DIDS>IAA-94>9-AC. Similarly, all the tested AT blockers inhibited (36)Cl(-) uptake from the midgut lumen in fifth-instar larvae when fed for 3 h on treated diet. Concentrations required for 50% inhibition of (36)Cl(-) uptake (IC(50)) ranged between 7.4 and 11.0 ppm and the rank order of activity was DIDS>NPPB>9-AC >IAA-94. Modest to highly strong positive correlations observed among growth, midgut alkalinity, and midgut Cl(-) ion transport in AT blocker-fed larvae suggested that these effects are causally related to each other. Finally, AT blockers have the potential to become good candidates for development of insecticides with a unique mode of action.