Methyl salicylate fails to enhance arthropod predator abundance or predator to pest ratios in cotton

Authors: Naranjo, Steven; Hagler, James; BYERS, JOHN - Retired ARS Employee

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2020
Publication Date: 4/26/2021
Citation: Naranjo, S.E., Hagler, J.R., Byers, J. 2021. Methyl salicylate fails to enhance arthropod predator abundance or predator to pest ratios in cotton. Environmental Entomology. 50(2):293-305. https://doi.org/10.1093/ee/nvaa175.
DOI: https://doi.org/10.1093/ee/nvaa175

Interpretive Summary: Crop plants produce a variety of volatile chemical signals when they are fed upon by herbivorous pest insects. Some of these chemicals act as attractants for insect predators and parasitoids and can benefit the plant by killing and consuming the herbivores. Synthetic versions of some of these volatiles are commercially available, include methyl salicylate (MeSA). It is thought that application of these chemicals in crop system can improve biological control by attracting natural enemies of the pest. We tested this idea over a two-year period in cotton by comparing field plots containing MeSA lures to those without and measuring the abundance of both natural enemies and two of the key pests of cotton in the western U.S. We verified that MeSA was being emitted in our study plots, but we found no difference in the abundance of either natural enemies or pests in either year. In the second year our study plots surrounded a large alfalfa field. Alfalfa is known to harbor large numbers of natural enemy species also found in cotton. Even with this large source of natural enemies nearby we failed to find higher numbers of predators and parasitoids in cotton treated with MeSA. We also examined predator to pest ratios as a proxy for potential biological control activity. We generally found that predator to pest ratios did not differ due to MeSA, but we found that the ratio of minute pirate bugs (a common predator) and whitefly adults (a key pests) was elevated in the MeSA treated plots and this would suggest that insecticide use could potentially be delayed in this situation. Aside from this single benefit our overall results suggest that MeSA would not likely enhance conservation biological control by the natural enemy community typical of U.S. western cotton production systems. This information would be useful to growers, pest control advisor and extension personnel involved in cotton integrated pest management.

Technical Abstract: Conservation biological control is fundamental tactic in integrated pest management (IPM). Greater biological control services can be achieved by enhancing agroecosystems to be more favorable to the presence, survival and growth of natural enemy populations. One approach that has been tested in numerous agricultural systems is the deployment of synthetic chemicals that mimic those produced by the plant when under attack by pests. These signals may attract arthropod natural enemies to crop habitats and thus potentially improve biological control activity locally. A two-year field study was conducted in the cotton agroecosystem to evaluate the potential of synthetic methyl salicylate (MeSA) to attract native arthropod natural enemies and to enhance biological control services on two key pests. Slow-release packets of MeSA were deployed in replicated cotton plots season-long. The release of MeSA and several cotton plant volatiles were quantified during the season by gas chromatography - mass spectrometry. The abundance of multiple taxa of natural enemies and two major pests were monitored weekly by several sampling methods. The deployment of MeSA failed to increase natural enemy abundance and densities of the pests did not decline. Predator to prey ratios, used as a proxy to estimate biological control function, also largely failed to increase with MeSA deployment. One exception was a season-long increased the ratio of Orius tristicolor (White) to Bemisia argentifolii Bellows and Perring (= Biotype B Bemisia tabaci) adults within the context of biological control informed action thresholds. Overall results suggest that MeSA would not likely enhance conservation biological control by the natural enemy community typical of U.S. western cotton production systems.