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The mobility of a pesticide in soil is determined by the extent and strength of sorption, which is influenced by either the existing soil humus or exogenous humic substances. Exogenous humic acids (HAs) were added to soil to enhance the amount of soil organic carbon (SOC) by 2.5, 5.0 and 10.0 g kg ) when the soil solution pH was 6.0. However adsorption of imidacloprid in the HA treatment was higher than the controls. Imidacloprid adsorption was usually higher under lower pH and/or lower temperature at same condition. Imidacloprid sorption fitted the Freundlich isotherm, indicating that exogenous humic substances influenced adsorption of imidacloprid, which in turn was affected by environmental conditions such as pH and temperature. Thus, exogenous HA can be used to control the mobility of soil pesticide under appropriate conditions to decrease pesticide pollution diffusion and probably increase effectiveness of pesticides.

Exposure to insecticides is the main cause of honeybee (Apis mellifera) population decline. At sub-lethal doses, these chemicals have been shown to negatively affect honeybee physiological development and behavior. Previously, we found the insecticide imidacloprid and deltamethrin significant reduced honeybee dancing and foraging efficiency. As a follow up, we performed a deep RNA-seq analysis to reveal the gene regulatory mechanisms underlying the altered foraging behavior. Genes involved in detoxification were up-regulated in both imidacloprid and deltamethrin treatment groups. Gene members in immune pathways, odorant receptors and major royal jelly protein families showed significant up or down regulation in treatment groups compared with controls. This fluctuating gene expression profile reflects that multifaceted aspects of honeybee physiology were affected by the two insecticides, leading to inaccurate communication and impaired learning and memory. Our findings reveal candidate molecular mechanisms under impaired dance performance in honeybees exposed to insecticides.

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