Sub-lethal effects of four neonicotinoid seed treatments on the demography and feeding behaviour of the wheat aphid Sitobion avenae

Abstract

Neonicotinoids are widely used as seed treatments in wheat fields against the grain aphid (Sitobion avenae F.) in China. Due to the degradation of neonicotinoids in wheat plants, wheat aphids are more likely to be exposed to low concentrations of neonicotinoids over long periods. It is therefore expected that neonicotinoids, aside from acute (lethal) effects, may also cause a range of sub-lethal effects on this pest. The growth and fertility of S. avenae feeding on wheat plants treated with a sub-lethal concentration (LC10 ) of imidacloprid, dinotefuran, thiacloprid and thiamethoxam were not greatly affected. However, the population growth parameters of S. avenae were significantly reduced at median lethal concentration (LC50 ). Electronic penetration graph recordings showed a higher percentage of no probing phase and shorter phloem sap ingestion phase on the wheat plants treated with LC10 and LC50 concentrations. The results indicate that even low concentrations of neonicotinoid treatments on wheat seeds have long-term, adverse effects on wheat aphid. As such, neonicotinoid seed treatments have far greater effects on wheat aphids than estimated by acute toxicity tests. These results benefit our understanding on the subtle effects of the four tested neonicotinoids when applied as seed treatments.