Evaluation of Residue Levels of Imidacloprid and Thiamethoxam After Foliar Application to the Citrus Varieties Lane Late, Valencia Late, Rohde Summer, and Nules

Abstract

Neonicotinoids are used to protect citrus trees against pests. Dissipation and persistence of neonicotinoids in pollen and nectar of citrus trees after foliar applications and their potential exposure to pollinators have not been well characterized. Field studies were conducted using three orange and one mandarin varieties to compare the imidacloprid and thiamethoxam residue levels and their decline in pollen and nectar after treatments in pre-bloom close to flowering period and their persistence 1 yr after treatment. The possible risk to honeybees was assessed. In nectar, thiamethoxam and imidacloprid residues were between 61 and 99% lower than in pollen, depending on the citrus variety or/and the days after treatment when applied close to blooming. At the end of the flowering period, imidacloprid in pollen and nectar was not detected in the mandarin variety after treatment in pre-bloom, whereas for thiamethoxam, no residues were detected in nectar but 10 ng/g was detected in pollen. There were no quantifiable levels of residues for either neonicotinoids in pollen or nectar during the flowering period of the following year. Neonicotinoid residue levels and their decline in nectar and pollen in citrus depended on the timing of applications relative to flowering and on the citrus variety. The absence of neonicotinoid residues 1 yr out after foliar applications in all varieties assayed demonstrated that none of the neonicotinoids tested were persistent. The results could be different in other citrus varieties, and therefore, also the exposure assessment for managed pollinators.

Neonicotinoid contamination in wildflowers collected from citrus orchards in a northwestern Mediterranean Region (Spain) after tree foliar treatments

“…In a previous study in these citrus orchards, it was found that nectar or pollen of citrus trees sprayed with imidacloprid and thiamethoxam, at the same doses that in this study, contained no neonicotinoid residues after 230 days (Martínez-Ferrer et al 2019). The data provided in the present study on the neonicotinoid residue levels found in wildflowers at 230 and 336 days show that, in some cases, groundcover vegetation may represent a more important route of pesticide chronic exposure for non-target arthropods than the crop itself.…”

“…At 22 dat, when all the wildflower species included in this work could be compared, different neonicotinoid levels between them were found, indicating that the accumulation of each neonicotinoid depends on the species. Differences in neonicotinoid concentrations in pollen and nectar of citrus flowers from different varieties were also found after neonicotinoid application (Martínez-Ferrer et al 2019). Li et al (2018) reported that the amount of imidacloprid taken up by vegetables differed with the variety of vegetable and its growth stage, and it is related to the evapotranspiration and availability of imidacloprid in roots.…”