Insecticidal activity of glufosinate through glutamine depletion in a caterpillar

Abstract

The herbicide glufosinate-ammonium (GLA) is a competitive inhibitor of glutamine synthetase (GS), an enzyme converting glutamate to glutamine in both plants and animals. Because GS is essential for ammonia detoxification in plants, GLA treatment disrupts photorespiration by causing a build-up of ammonia and a loss of glutamine in plant tissues. This study reports that GLA applied to leaf surfaces is also toxic to 5th-instar caterpillars of the skipper butterfly Calpodes ethlius (LD50 = 400 mg kg-1). After ingesting GLA, caterpillars stopped feeding and became dehydrated through a loss of rectal function. Caterpillars showed symptoms of neurotoxicity, such as proleg tremors, body convulsions and complete paralysis before death. Incubation of several tissues isolated from normal feeding-stage caterpillars with the GS substrates glutamate and ammonium showed that GLA inhibited GS activity in vitro. Within 24 h of ingesting GLA, caterpillars had a greatly reduced glutamine content and the ammonium ion levels had more than doubled. Injection of ammonium chloride into non-GLA-treated caterpillars had no deleterious effect, suggesting that glutamine depletion, and not a rise in body ammonium, was the primary cause of GLA toxicity following GS inhibition. This was supported by the observation that the onset of the symptoms of GLA poisoning could be postponed by giving GLA-fed caterpillars several subsequent daily injections of glutamine. The effective GLA dose fed to 5th-instar caterpillars in this study was comparable to the amount that might realistically by acquired from feeding on GLA-treated crops.

Active role of fatty acid amino acid conjugates in nitrogen metabolism in Spodoptera litura larvae

“…This could be because glutamic acid generally functions as a neurotransmitter in hemolymph, and too much glutamic acid might cause cytotoxicity in insects (26). Disorder in GS function and glutamine shortage can easily cause death (30). Therefore, we wondered whether FACs with an obvious active role in nitrogen metabolism might even improve GS productivity in insects.…”

Monarch Butterflies Use Regenerating Milkweeds for Reproduction in Mowed Hayfields in Northern Virginia

“…These studies were done with the active ingredient, not a full formulation, and so may have underestimated field toxicity (Kutlesa and Caveney 2001). Although monarchs will not use these crops as host plants for larvae, glufosinate may accumulate in nectar, pollen and guttation liquid of treated crops and be consumed by monarch butterflies.…”

Global nutrient profiling by Phenotype MicroArrays: a tool complementing genomic and proteomic studies in conidial fungi

“…To show the utility of PM for chemical inhibitor analysis, Tanzer et al (2003) compared the responses of A. nidulans and M. grisea to the addition of the growth inhibitor glufosinate. Glufosinate (phosphinothricin) is a herbicidal compound that has also been shown to inhibit animal and fungal growth (Avalos et al, 1989;Pall, 1993;Kutlesa and Caveney, 2001). It is an analogue of L-glutamate that inhibits glutamine synthetase, thereby preventing the synthesis of glutamine and consequently the synthesis of numerous other nitrogenous compounds required for growth.…”