Abstract
Thiacloprid (TCL) uptake by maize plants that emerge from coated seeds has been investigated and characterized via measurements of the compound in the guttation liquid. TCL levels were determined in the guttation liquid: (a) under field and semi-field conditions, (b) for different maize varieties, (c) applying different dosages, and (d) as affected by cross-contamination between maize seeds via soil. Cross-contamination was described by uptake interactions between seeds coated with TCL and neighboring seeds not coated or coated with other neonicotinoids, e.g., either thiamethoxam (TMX) or clothianidin (CLO). TCL levels remained under 100 µg/mL in the guttation liquid under field conditions, and were quantifiable even on the 39th day after planting of coated seeds. Higher levels up to 188.6 µg/mL were detected in plants grown under semi-field conditions in pots. Levels in the guttation liquid were also found to be influenced by the applied dosages. The uptake of TCL was found to vary for different maize varieties. Appearance of TCL as a cross-contaminant in the guttation liquid of neighboring plants emerging from non-coated maize seeds indicates translocation of the compound via soil. Peak levels of TCL cross-contamination were found to be lower (43.6 µg/mL) than the corresponding levels in the parent maize plants emerging from coated seeds (107.5 µg/mL), but values converge to each other. Similar trends were observed with neighboring seeds coated with other neonicotinoids (TMX or CLO). The translocation rate of TCL and its uptake by other plants seem to be lower than that of TMX or CLO.
Highlights
Neonicotinoids are currently among the most widely used insecticides in the world
We have previously described cross-contamination with neonicotinoids from neighboring maize seeds coated with TMX and/or CLO [35] and between maize seeds coated with TMX or CLO and neighboring weeds [40]
Levels in the guttation liquid of maize seeds coated with TCL are quantifiable even one month after planting of coated seeds under field conditions
Summary
Neonicotinoids are currently among the most widely used insecticides in the world. Their use remarkably increased in the last decades, whereas organophosphates and carbamates have lost market share [1] due to pest resistance developed by different insect species. Metabolomic resistance, e.g., enhanced monooxygenase activity [3], appears much more common than mutation of the target site (insect nicotinic acetylcholine receptors) [2] Due to their extended use and high leaching potential from soils of low organic content [4,5,6], neonicotinoids became ubiquitous contaminants worldwide in surface waters [7]. Application of alternative pest management strategies was suggested recently [15] to eliminate neonicotinoid-based chemical pest control in cropping systems. These tools provide considerable reduction in the use of these insecticides avoiding
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