Risk Assessment of Spotted Lanternfly (Lycorma delicatula) Neonicotinoid Control Tactics on Non-Target Insect Floral Visitors of Red Maple (Acer rubrum) and Tree-of-Heaven (Ailanthus altissima)
Open Access
- Author:
- Elmquist, Jon
- Graduate Program:
- Entomology
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 06, 2022
- Committee Members:
- Gary Felton, Program Head/Chair
Kelli Hoover, Thesis Advisor/Co-Advisor
Julian D Avery, Committee Member
David Biddinger, Thesis Advisor/Co-Advisor - Keywords:
- neonicotinoid
insecticide
spotted lanternfly
imidacloprid
dinotefuran
pollinator
red maple
tree-of-heaven
Acer rubrum
Ailanthus altissima
Lycorma delicatula
non-target
risk assessment - Abstract:
- Systemic neonicotinoid insecticides are used in the US for management of spotted lanternfly (Lycorma delicatula; SLF), a phloem-feeding planthopper and recent invasive pest of economic importance. Tree-of-heaven (Ailanthus altissima), a highly preferred host of spotted lanternfly and a widespread invasive tree in the US, is treated with the neonicotinoid dinotefuran by professional applicators under the direction of the US Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) and several state agricultural departments. Application of the neonicotinoids imidacloprid or dinotefuran may be recommended by extension services for the protection of ornamental trees against SLF, such as red maple (Acer rubrum), a common eastern US native and important nutritional resource for early spring emerging bees. Since the introduction of neonicotinoids, much evidence has been gathered showing their potential for harm to non-target beneficial invertebrates, particularly bee pollinators, which can be exposed via contaminated floral resources in treated trees. But potential impacts of systemic neonicotinoid applications to trees for SLF control to non-target floral visitors has been largely unexplored. Therefore, I sought to determine the levels of neonicotinoid residues in flowers of tree-of-heaven and red maple treated with neonicotinoids for SLF control and identify the floral visitors to these trees to provide an assessment of their potential risk. To accomplish this, neonicotinoid residue concentrations were determined in whole flowers of tree-of-heaven and red maple following post-bloom applications of dinotefuran or imidacloprid which differed in timing and method of application. Application timing, but not method of application, significantly influenced neonicotinoid residue concentrations in flowers of treated red maple, with dinotefuran residues significantly higher from red maple treated in fall than summer and imidacloprid residues significantly higher from red maple treated in spring or summer than fall. In the tree-of-heaven we sampled, neonicotinoid residues were only found in flowers of one tree, at 2.75 ppb. Acute risk quotients were calculated from mean (+ 95% confidence interval) neonicotinoid residue concentrations determined in flower samples for each relevant treatment group. Dinotefuran and imidacloprid LC50s for honey bees (Apis mellifera) and Japanese orchard bees (Osmia cornifrons) were determined via 48-hour ingestion bioassays and I compared these risk quotients to a specified level of concern, which is a method similar to those used by North American regulatory agencies for assessing pesticide risk to bees. No risk quotients calculated for honey bees for any relevant treatment group exceeded the level of concern, indicating minimal acute risk of mortality to honey bees, which is a surrogate for social bee species, from exposure to neonicotinoid residues at levels found in the whole flowers sampled. In contrast, several risk quotients calculated for O. cornifrons exceeded the level of concern, indicating potential for acute risk to O. cornifrons, a surrogate for solitary bee species, from exposure to neonicotinoid residues at levels found in whole flowers sampled from several treatment groups. To determine the floral visitors of red maple and tree-of-heaven that could be exposed to neonicotinoid residues in flowers of these trees treated for SLF control in Pennsylvania, observations of insect visits to flowers and collections and identifications of insect visitors to flowers of these trees were conducted. The dominant floral visitor of tree-of-heaven in southeastern Pennsylvania was the margined leatherwing beetle (Chauliognathus marginatus), followed in abundance mostly by bee hymenopterans, especially the small bee genera Halictus and Lasioglossum, in addition to flies. The most abundant floral visitors to red maple flowers were bee hymenopterans, mostly honey bees and Andrena spp., and flies. These floral visitor groups are the most likely insects to be exposed to neonicotinoid residues in flowers of red maple and tree-of-heaven treated for SLF control in Pennsylvania. The results of this work suggest that some bee floral visitors of red maple may be at risk of mortality from acute exposure to neonicotinoid residues found in flowers of this tree species treated with post-bloom applications of imidacloprid or dinotefuran for SLF control and that this risk may be impacted by several factors, particularly application timing. More, well-replicated studies are recommended to provide more comprehensive risk assessments to non-target beneficial insects from neonicotinoid use in SLF management and explore reduced-risk alternatives for SLF control.