Differential effects of butyric acid on nematodes from four trophic groups

Abstract

Butyric acid, which is produced through fermentation of organic matter by anaerobic soil bacteria, possesses nematicidal properties. We investigated how the concentration of butyric acid in solution and gas phase affected the survival of 12 nematode species from four trophic groups. Our hypothesis was that survival of free-living and plant parasitic nematodes would differ, since free-living nematodes have shown some adaptation to survival in anaerobic soil environments. A 2-day incubation in sand amended with 0.88 mg butyric acid g −1 reduced plant parasitic and fungivorous nematodes by 84–100% as compared to untreated controls, whereas a concentration of 8.8 mg butyric acid g −1 was necessary to significantly reduce bacterivorous nematodes (70–98%). Sensitivity of entomogenous nematodes was variable, with Heterorhabditis adversely affected by 0.88 mg butyric acid g −1 sand, resulting in a 59% reduction, while Steinernema required a concentration of 8.8 mg butyric acid g −1 sand to see a significant decline (85%). Results were similar when nematodes were exposed to the gas phase of butyric acid for 7 days. The vapor from a 0.1 M solution reduced plant-parasitic and fungivorous nematodes by 89–96% while the vapor from a 1 M solution of butyric acid reduced entomogenous nematodes by 94–99%. Bacterivorous nematodes did not survive the 7-day incubation period in appreciable numbers in either controls or treated sand. A 2-day incubation of nematodes in sand acidified with HCl to achieve pH values of 3.4 and 3.0 (similar to sand amended with 0.88 and 8.8 mg butyric acid g −1 sand) had no effect on nematode survival in any of the trophic groups tested. A positive correlation was found between LC 50 values for butyric acid and nematode surface area-to-volume ratios for four out of five plant parasitic nematodes ( r=0.99; P=0.01) and a negative correlation was found for bacterivorous, entomogenous and fungivorous nematodes combined ( r=−0.77; P=0.07). The differentiation in chemical tolerances demonstrated here may hold a key to targeting plant parasitic nematodes without affecting free-living forms.