Spatial and Temporal Distribution of Residues of Imidacloprid and Its Insecticidal 5-Hydroxy and Olefin and Metabolites in Eastern Hemlock (Pinales: Pinaceae) in the Southern Appalachians

Abstract

Widespread mortality of eastern hemlock, Tsuga canadensis (L.) Carrière, resulting from infestation by hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), has occurred throughout the native range of eastern hemlock within the eastern United States. Imidacloprid, a systemic insecticide, is one of the primary chemical compounds used to control hemlock woolly adelgid in both urban and, in a limited manner, in natural forest environments. The metabolism of imidacloprid in eastern hemlock produces 12 metabolites; two of these, imidacloprid 5-hydroxy and imidacloprid olefin, are considered toxicologically important metabolites. However, little is known about the persistence of these metabolites in eastern hemlock in the southern Appalachians. Concentrations ofimidacloprid, olefin, and 5-hydroxy were quantified by using HPLC/MS/MS techniques. Over the 3-yr study, concentrations of imidacloprid and consequent 5-hydroxy and olefin were highest in trees treated with a soil injection in the spring. Imidacloprid and 5-hydroxy concentrations in sap were highest at 12 mo posttreatment and in tissue at 15 mo posttreatment. Imidacloprid was detected through 36 mo posttreatment and 5-hydroxy was detected through 15 mo posttreatment. Olefin concentrations in both sap and tissue were highest at 36 mo posttreatment and were detected in high concentrations through 36 mo posttreatment. Concentrations of imidacloprid were highest in the bottom stratum of the canopy and lowest in the top stratum. Concentrations of olefin and 5-hydroxy were highest in the top stratum and lowest in the bottom stratum.

Concentration Levels of Imidacloprid and Dinotefuran in Five Tissue Types of Black Walnut, Juglans nigra

“…Using the formula outlined by Schöning and Schmuck [27], imidacloprid, olefin-imidacloprid, and dinotefuran residuals in parts per billion (ppb) were determined using the average peak areas of imidacloprid and dinotefuran conversions for each analyte [25]. Imidacloprid, olefin-imidacloprid, and dinotefuran concentration data were converted from ng g −1 of each analyte (dry weight) to ppb and placed into an Excel ® file and analyzed using Proc Mixed ANOVA in SAS [29].…”

“…For example, average imidacloprid concentrations ranged from 8.0 to 134.0 ppb and olefin-imidacloprid concentrations ranged from 2.0 to 4.5 ppb. However, olefin-imidacloprid concentrations have been documented to progressively increase as imidacloprid concentrations decreased over time [25]. The olefin-imidacloprid metabolite, one of 12 known metabolites of imidacloprid, has been reported to be at least ten times more active than its parent compound against the green peach aphid, Aphis gossypii Glover [34], and 13 times more active against hemlock woolly adelgid [25].…”

“…However, olefin-imidacloprid concentrations have been documented to progressively increase as imidacloprid concentrations decreased over time [25]. The olefin-imidacloprid metabolite, one of 12 known metabolites of imidacloprid, has been reported to be at least ten times more active than its parent compound against the green peach aphid, Aphis gossypii Glover [34], and 13 times more active against hemlock woolly adelgid [25]. Another metabolite, i.e., 5-hydroxy-imidacloprid, has been documented to be slightly less active than the parent imidacloprid; however, 5-hydroxy-imidacloprid still retains relatively high toxicological properties [25].…”

“…The olefin-imidacloprid metabolite, one of 12 known metabolites of imidacloprid, has been reported to be at least ten times more active than its parent compound against the green peach aphid, Aphis gossypii Glover [34], and 13 times more active against hemlock woolly adelgid [25]. Another metabolite, i.e., 5-hydroxy-imidacloprid, has been documented to be slightly less active than the parent imidacloprid; however, 5-hydroxy-imidacloprid still retains relatively high toxicological properties [25]. This paper is the first report of olefin-imidacloprid in tissue of any deciduous tree and infers longer-term residual effects that could result in longer control of pest insects due to the toxicity of imidacloprid's metabolites.…”

“…However, little is known regarding the movement of these two systemically applied pesticides, imidacloprid and dinotefuran, within the black walnut tissue. Additionally, little is known about the imidacloprid metabolite, olefin-imidacloprid, which is reported to be more toxic than imidacloprid [25], and it is unknown at what levels and for how long olefin-imidacloprid can remain within deciduous plant material, including nutmeat. Although research has been conducted on the spatial and temporal movement of imidacloprid in eastern hemlocks, Tsuga canadensis L., [26], it is important to understand the movement of imidacloprid and its derivative chemicals, i.e., olefin-imidacloprid, through black walnuts if they are going to be considered for control of wood-boring insects associated with TCD.…”