Leaf herbivory by Spodoptera litura increases arbuscular mycorrhizal colonization in roots of soybean

Abstract

The improvement of host plant growth resulting from mycorrhizal colonization often affects the viability of above-ground herbivorous insects. Conversely, the effects of herbivorous insects on plant growth may indirectly affect below-ground microorganisms. This study investigated the effects of herbivorous insects on arbuscular mycorrhizal (AM) colonization of soybean (Glycine max Merr.). Seeds of soybean were sown in soil inoculated with the AM fungus Gigaspora margarita Becker & Hall and grown in growth chambers. At 39 days after inoculation (DAI), a larva of the common cutworm (Spodoptera litura Fabricius) was placed on a leaf of each soybean plant for 5 days. AM colonization of soybean on 39 DAI was 21%. Although not evident by 62 DAI, by 77 DAI there was a statistically significant increase in AM colonization in plants subjected to herbivory by S. litura relative to control plants. Leaf removal at 46 DAI was also associated with increased AM colonization at 78 DAI. These results suggest that herbivory by chewing insect affects AM colonization and that the effect is likely caused by a decrease in leaf area.