engleski

Neonicotinoid degradation dynamics in sugar beet plants grown from treated seeds and influence on harmful and beneficial fauna

Sugar beet (Beta vulgaris var. saccharifera L.) is a profitable industrial crop, but also one of the most demanding, considering the production technology and the growing period of almost 180 days. Sugar beet is attacked by numerous pests such as wireworms, sugar beet flea beetles, aphids, and others, which significantly reduce yield, root quality and sugar content. In the last 20 years, sugar beet protection has been successfully carried out using the method of seed treatment with neonicotinoids (imidacloprid and thiamethoxam). Because they are suspected of having negative effects on bee colonies and other beneficial organisms, the EC regulation prohibits their use starting in 2019, except in permanent greenhouses or with special permission. Among the most important beneficial soil fauna of sugar beets are ground beetles and earthworms, which have an indirect positive impact on the crop by increasing soil fertility, regulating the water- air ratio or reducing the number of pests. Due to the ban on neonicotinoids, sugar beet production has halved compared to previous years, amounting to only 10, 000 hectares.The environmental assessment of plant protection products for soil organisms is mainly based on the results of laboratory and extended laboratory studies, while the link from the laboratory to realistic field conditions over several seasons is not well established. Despite the ban, the degradation dynamics of neonicotinoids in plants sown from treated seeds and their effects on these plants and the surrounding soil are still not well understood. Moreover, the residues of neonicotinoids and their bioaccumulation in beneficial soil fauna in Croatia have not yet been determined, nor has their impact on the numbers and composition of these organisms. Therefore, the objectives of this research were: (i) to determine the efficacy of neonicotinoids on the main pests and the degradation dynamics in sugar beet plants grown from seeds treated with imidacloprid and thiamethoxam under different weather conditions ; (ii) determine the residues of neonicotinoids in ground beetles, earthworms, and soil of sugar beet fields ; and (iii) determine the cenological composition of ground beetles and the possibility of population recovery in sugar beet fields and fields included in a four-year crop rotation. Monitoring of neonicotinoid efficacy against major pests and degradation dynamics was conducted over two years (2015 and 2016) in Virovitica - Podravina (Lukač) and Vukovar - Syrmium (Tovarnik) counties and under laboratory conditions. Samples were collected using standard protocols, including pitfall traps for ground beetles and ISO - ISO 23611-1:2006 methodology for earthworm sampling. Residue analysis was performed using the LC-MS / MS SPE - QuEChERS method with LOQ of 0.01 mg/kg for plant and soil samples and 0.001 mg/kg for animal samples. A biocenological-synecological analysis of ground beetles was performed to determine the ecological indices of the population, and based on the calculated dominance, the represented species were classified according to Tischler and Haydeman. Collected samples were determined to species using standard dentification keys. Results were statistically analyzed using ANOVA. Results show that insecticide treatment of sugar beet seed leaves minimal residues in plants and is completely degraded by the end of the growing season. Elevated concentrations of residues in the soil indicate that in dry climates or after a dry period, there is a risk to crops that follow sugar beets in the rotation. All neonicotinoid residues detected in beneficial organisms were below levels considered lethal throughout the sampling period, so it can be assumed that insecticides do not accumulate in these organisms. Calculation of the bioconcentration factor using the retrospective analysis method of analytically measured neonicotinoid residues in the samples indicates that there is no risk to earthworms and no potential for secondary poisoning in birds and mammals that feed on them. The composition and abundance of ground beetles in sugar beet fields is strongly influenced by several factors during the growing season, with insecticides having negative effects, while reduced tillage, lower temperatures, and more rainfall lead to higher ground beetle abundance and diversity. Growing sugar beets in a four-year rotation provides a recovery in the ground beetle population. The research also resulted in a comprehensive list of 64 ground beetle determined to species in maize, sugar beets, wheat, and soybeans, and represents a valuable finding that complements previous studies in Croatia. A better understanding of ground beetles in intensive agricultural landscapes is a good starting point for conservation programs that have become standard in the European Union.

accumulation, bioconcentration, cenological analysis, degradation, earthworms, efficiency, ground beetles, neonicotinoids, pests, sugar beet, treated seeds

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