A Pesticide Residues Insight on Honeybees, Bumblebees and Olive Oil after Pesticidal Applications against the Olive Fruit Fly Bactrocera oleae (Diptera: Tephritidae).

Abstract

Simple SummaryOlive cultivation is extensive throughout the Mediterranean region and essential for the rural economy, local heritage and the environment. To control the olive fruit fly, a major threat for this cultivation, pesticides, in the form of bait or cover sprays, are applied. These pesticide applications can potentially impact pollinators that forage in the nearby areas or live inside the olive orchards. Based on current practice, olive trees supply shadow, water, and still support some flowering plants at the period of the year with the highest temperature and minimum nectar and pollen flow, which can be beneficial for bees. In this study pesticide residues were monitored in honeybees, bumblebees, honey and olive oil, after placement of bee colonies in Greek olive orchards where applications to control the olive fruit fly took place. Variations of concentrations were evidenced, for the three active ingredients that were applied. In limited cases, concentrations in bees higher than the median lethal dose can possibly be attributed to bait dose rates or broad foraging of bees in nearby orchards with similar applications. Determined olive oil residues corroborated that those pesticides were applied in the olive orchards.In 2017 and 2018, a field survey was initiated on Greek olive orchards to investigate the attractiveness of bait spray applications and the impact of cover and bait sprays applied against the olive fruit fly Bactrocera oleae (Diptera: Tephritidae), on the honeybee, Apis mellifera L. and bumblebees Bombus terrestris, by investigating the pesticides’ residual prevalence. Bee colonies were evenly distributed in three sites located on coastal areas of Western Crete and visited almost weekly between July and October. Samples collected, were analyzed using existing or developed-optimized liquid and gas chromatographic methods. In bee samples, concentrations varied from 0.0013 to 2.3 mg/kg for dimethoate, from 0.0013–0.059 mg/kg for its metabolite omethoate, and from 0.0035 to 0.63 mg/kg regarding the pyrethroids, β-cyfluthrin and λ-cyhalothrin. In one bee sample dimethoate concentration exceeded both acute oral and contact median lethal dose (LD50). Residue findings in bees, along with verified olive oil residues corroborated that those insecticides had been applied in the olive orchards and transferred to bees. The possibility of non-target effects of the bait sprays to the bees, as well as the impact of the contaminated olive to the bees are discussed.