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Investigation into potential non-target effects from the use of emamectin benzoate trunk injections for the management of emerald ash borer (Coleoptera: Buprestidae)

Date

2020

Authors

Al-akeel, Rasha, author
Cranshaw, Whitney, advisor
Kondratieff, Boris, advisor
Bjostad, Louis, committee member
Koski, Tony, committee member

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Abstract

A potentially significant source of increased conflict in Colorado involving insecticide use in urban areas and honey bees (Apis mellifera L.) recently emerged with the establishment of the invasive species emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Detected in Colorado in 2013, numerous concerns were quickly raised about potential non-target effects from the enormous increase in insecticide use on urban trees in the state that are used to manage this insect. A series of studies were conducted to address some of these and are presented in three chapters. Chapter I, focuses on the types of pollen that honey bees collect from urbanized sites in northern Colorado during the onset of flowering during late winter (early March) through mid-spring (early May), giving particular attention to the incidence of pollen collected by honey bees from ash (Fraxinus), which flowers at this time. This project found that some ash pollen is collected, averaging 9.9 percent of the total, during the earliest period when pollen sources first become available, in March and when green ash (Fraxinus pennsylvanica Marshall) is in flower. Incidence of ash pollen collection then dropped greatly, when a wider range of alternative pollen sources become available in the later blooming species white ash (Fraxinus americana L.). Important pollen sources were identified with early blooming Acer representing a very high proportion of pollen collected during late winter/early spring. Other notably common sources of pollen in samples included Prunus, Salix, and Brassicaceae. These first studies can also be used in plans to improve availability of early season pollen resources for honey bees and to identify plants that bloom coincident with ash and can provide alternative pollen for honey bees during periods of ash bloom. Chapter II examined whether there would be effects on decomposition of senesced green ash leaves collected during leaf fall from trees previously treated with trunk injections of insecticides (emamectin benzoate, azadirachtin). These involved a series of studies, using litterbags conducted over four years. There was no difference in leaf decomposition in the first two years, when litterbags had a mesh size (5mm) large enough to allow access by earthworms and they were shallowly buried; all leaf matter was completely degraded regardless of insecticide history. Subsequent trials in the following two years used litterbags with a smaller mesh size (2mm) designed to exclude earthworms but allow access by microarthropods involved in decomposition of leaf litter (e.g., Collembola, Oribatida). In addition, differences in litterbag placement (surface, shallow burial) and length of field exposure (90 days, 150 days) were included in the last two study years, which used foliage from two sites. In some, but not all, studies there were significant reductions (compared to the untreated control) in leaf area loss in litterbags of leaves collected from trees with a history of use of emamectin benzoate (TREE-äge) and azadirachtin (Tree-Azin), compared to the untreated control. Chapter III measured levels of emamectin benzoate residues present in different plant tissues collected from green ash: senescing leaves at leaf fall, flowers, and pollen. All samples of senescent foliage collected in October 2018, approximately four months after emamectin benzoate application, had detectable residues of emamectin benzoate but at levels never exceeding 1.1ppb. Sample collections of the trees made the previous season (October 2017), when a period of 16 months had passed since the insecticide application, detected far lower levels of residues. Levels of emamectin benzoate appearing in flowers was lower than that appearing in foliage and was detected only in 8 of 22 samples at the levels of quantification allowed in this analysis (0.28ppb). Among the 60 samples of pollen collected from trees that had been treated with emamectin benzoate, emamectin fragment ions were not detected at the Limit of Detection (LOD) attained with this analysis (0.1ppb). Together, these studies help answer several questions regarding potential non-target effects resulting from certain insecticide uses involved in management of emerald ash borer. These can be used to help in risk assessments and in ways to mitigate potential non-target effects.

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2020 Fall.
Includes bibliographical references.

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