Impact of Neonicotinoid Insecticides Residues Applied as Seed Treatments on Maize and on Bees and Hive Products

Abstract

" Romania registered in the last years record productions for maize, being in 2019, on the first place in Europe and also, according to Eurostat data, the eighth agricultural power in Europe. The European Commission closely monitors the possible relations between bee health and pesticides and is determined to take the most cautious approach possible to protect bees. In 2013, the European Commission severely restricted the use of plant protection products for seed treatment and treated seeds containing three neonicotinoids (clothianidin, imidacloprid and thiamethoxam) in order to protect honeybees (Regulation (EU) No 485/2013). Due to the restrictions imposed on Romanian farmers, they are facing an alarming increase in the population density of some soil pests, the most dangerous being Tanymecus dilaticollis and Agriotes spp., no other insecticides being available for maize seed treatment against T. dilaticollis in Romania. In this context, since 2018, the Ministry of Agriculture and Rural Development together with the Academy of Agricultural and Forestry Sciences funded researches to monitor populations of T. dilaticollis and Agriotes spp., but also the residues level of neonicotinoid insecticides from soil, plants in various development stages (leaves and inflorescences), as well as in bees and hive products (pollen, honey). Studies were performed in three areas of Romania, respectively, Moldova (Neamt County) and south of country (Calarasi County) where T. dilaticollis exceed the economic damage threshold (4-5 adults/sqm) and Subcarpathian hills (Arges county), where Agriotes spp. populations exceed the economic damage threshold (2-4 larvae/sqm), areas where maize is the main crop. Regarding the evolution of maize leaf weevil an wireworms population in the period 2018-2020, from the data obtained it can be observed that the number of adults/sqm has remained above the economic damage threshold. Regarding neonicotinoids residues monitoring, the samples were taken from maize crops at various growth stages, including inflorescences, from bees, pollen and honey samples, too. Residues levels were determined in accredited laboratories from Germany, France and Bulgaria using certificated methods. Of the total samples, most with residues content above LOQ (limits of quantification), are soil samples, an absolutely normal situation, as the neonicotinoids were applied as seed treatment. It is also very important to mention that the lowest percentage of samples with residues above the limit of quantification, was recorded in inflorescences, honey and bees samples, the annual deviations being insignificant. It has to be highlighted that the environmental factors, especially the humidity, influenced the repeatability of the results (for example: the rainfalls during the sowing period favored the toxic substances levigation in soil)."