**1. Introduction**

Sugar beet (*Beta vulgaris* var. *saccharifera* L.) is an economically viable crop produced mainly for white sugar. The world's leading sugar beet producers (France, Germany and Poland) account for almost 50% of total world production (111.7 million tons in 2016). However, only 20% of the world's sugar comes from sugar beet; 80% is produced from sugar cane [1]. Given the production technology and the length of the growing season of almost 180 days, sugar beet is considered the most intensive agricultural crop [2].

The economically important pests of South East Europe sugar beet include wireworms, pigmy mangold beetle, sugar beet and corn weevil, black beet weevil, alfalfa snout beetle, several species of noctuid moths, sugar beet flea beetle, aphids, and beet cys<sup>t</sup> nematode [3–11]. Their appearance depends on the region and the year.

Since the introduction of neonicotinoid seed treatment in the 1990s, there has been a strong decrease in insecticide use in Croatia [12]. Wireworms, aphids, and flea beetles were successfully controlled by neonicotinoid seed treatments [7,13–15] so additional treatment was only required in the case of severe infestation of some foliar pests that cannot be successfully controlled with neonicotinoids (e.g., sugar beet weevil) [16]. In north-western Europe, only aphids require occasional control with foliar insecticides [17].

Seed treatment is a method that has brought many advantages to modern agriculture [18–24], although there are some negative e ffects as well. In heavy infestations the e fficacy against wireworms and sugar beet weevil is weak, so additional protection measures are necessary [7]. It is often applied at higher rates [24] or when control is not even necessary.

The use of neonicotinoids has become a major controversy because of their negative e ffects on bees, other pollinators, and possibly other non-target organisms [25–27]. According to the available evidence and a risk assessment carried out by EFSA, the use of neonicotinoid pesticides (clothianidin, imidacloprid, and thiamethoxam) was severely restricted by European Commission (EC) in 2013 by the implementation of Directive 485/2013 [28]. The restriction applied to bee-friendly crops such as maize, oilseed rape, and sunflower, with the exception of greenhouse crops and the post-flowering treatment of certain crops, and to winter cereals. Based on the EFSA peer review of the pesticide risk assessment carried out for clothianidin [25], imidacloprid [26], and thiamethoxam [27], the Commission adopted on 30 May 2018, regulations banning completely the outdoor use of imidacloprid, clothianidin, and thiamethoxam to protect domestic honey bees and wild pollinators [29]. The only risk identified by EFSA for the treatment of sugar beet seeds with neonicotinoids was the risk of succeeding crop scenario [25–27].

In the succeeding crop scenario, the residues of neonicotinoids are expected to remain in the soil and be absorbed by the succeeding crop or weeds in the same field. Thus, if the significant concentrations of neonicotinoids were to remain in the soil after the growing season, they could be adsorbed by the succeeding crop (or weeds) from the soil and then the neonicotinoids could be found in pollen or excreted in guttation fluid.

The Commission has not considered the possibility of proposing further options in addition to the total ban on the treatment of sugar beet seed with neonicotinoids. This decision could endanger sugar beet production. The ban was justified by the fact that some ecologically more acceptable substitute chemicals (diamides) are e ffective in controlling the most serious pests and that tools to control most pests are available under integrated pest managemen<sup>t</sup> (IPM). However, the arguments do not fully apply to all economically important pests that damage sugar beet production in all production areas in the EU.

Hauer et al. [17] discussed neonicotinoid seed treatments in European sugar beet cultivation with regard to their e ffectiveness against target pests and their impact on the environment. They proposed to develop monitoring systems and models to identify regions (and years) with a higher risk of occurrence of pests and to allow the use of insecticide seed treatments only when high pest pressure is likely. In their analysis, Hauer et al. [17] only looked at sugar beet production in northwestern European countries and did not consider the di fferent climatic conditions and the occurrence of pests in eastern and southeastern Europe, where problems in production are mainly caused by flea beetles and sugar beet weevils. This fact makes their proposal even more important.

The aim of this research was to determine the residue levels of imidacloprid and thiamethoxam used as a seed treatment in sugar beet plants in di fferent agroclimatic regions in order to estimate environmental risk and possible transfer to other crops. Greenhouse trials have been established in order to provide insight to neonicotinoid behavior in controlled conditions.

#### **2. Materials and Methods**

#### *2.1. Field Site and Experimental Design*
