Data from five laboratory bioassays and three field mesocosm studies performed by Dr. Patrick Moran of the USDA-ARS Invasive Species and Pollinator Health Research Unit, to examine the toxicity of five herbicides (2,4-D, glyphosate, imazamox, penoxsulam and diquat) and two surfactants that are often applied with herbicides (a paraffinic-oil based one and a vegetable oil-based one) to the planthopper Megamelus scutellaris (Hemiptera: Delphacidae) released in the US for biological control of waterhyacinth (Eichhornia crassipes or Pontederia crassipes) an invasive floating aquatic weed. The studies were performed between 2016 and 2021 to support integrated management of waterhyacinth in the Sacramento-San Joaquin Delta of northern California. The planthopper has also been released in Florida and Mississippi, and in South Africa. Herbicide applications are often still necessary where this planthopper and other biocontrol agents have been released. The research question was 'can the planthopper survive exposure to the herbicides and surfactants?'. In lab bioassays, planthoppers from greenhouse colonies were exposed to herbicide-dipped leaves for 24 hours and then allowed to feed for six days on untreated plants. Planthoppers were then collected, frozen and counted. Exposure to diquat or the paraffinic oil-based surfactant caused 40% to 69% greater mortality than did exposure to water-dipped leaves in more than one trial, while the other four herbicides and the vegetable oil-based surfactant were not toxic. In field mesocosm tests, mesocosms were established in 21L tanks caged with mesh tents, and plants allowed to grow for 4 weeks. Between 150 and 240 adult planthoppers were then released into each mesocosm. The following day, mesocosms were sprayed with herbicide, surfactant or insecticide solutions or an insecticide positive control. Three days later, planthoppers were collected with vacuums, frozen and counted. Only treatment with the paraffinic oil-based surfactant reduced final counts (by 36% to 49%) in a manner that was statistically significant compared to water-sprayed mesocosms in more than one mesocosm field trial, along with the insecticide positive control (by up to 98%). Diquat reduced final counts by 64% in one trial. The results indicate that, with the possible exception of diquat, exposing planthoppers to herbicides does not cause significant mortality, consistent with prior regulatory evaluations of these herbicides as being safe for insects. A surfactant that is often applied with the herbicides is toxic to the planthopper, consistent with expectations that this surfactant, designed to break down plant waxes on leaf surfaces, is likely also harmful to insect cuticular waxes, which insects rely on to contain body fluids. Leaving unsprayed refuges for the planthopper may be a useful component of integrated waterhyacinth control programs. Resources in this dataset:

Resource Title: Data dictionary for dataset on toxicity of five herbicides and two surfactants towards the planthopper Megamelus scutellaris File Name: Data dictionary for AgPub archive plain text.txt Resource Description: Plain text file providing definition of each column in the data file and further information.

Resource Title: Toxicity of herbicides and surfactants to the waterhyacinth planthopper Megamelus scutellaris File Name: Waterhyacinth planthopper herbicide toxicity data PMoran.csv Resource Description: Five herbicides, two surfactants tested, along with a negative control (water exposure) and, in some tests, a positive control (insecticide)