Effects of lithium chloride on Apis mellifera ligustica (Hymenoptera: Apidae) based on proboscis extension response behavior
Author of the article:YU Tian-Tian； HOU Meng-Shang；ZHANG Meng；HU Shan-Shan；LI Zhi-Guo；SU Song-Kun
Author's Workplace：College of Bee Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China；College of Bee Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China；College of Bee Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China；College of Bee Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China；College of Bee Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China；College of Bee Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China
Key Words：Apis mellifera ligustica; lithium chloride; sucrose response scores; learning behavior; memory behavior; proboscis extension response
Abstract：
[Objectives] Ziegelmann et al. found that 25 mmol·L－1 lithium chloride had an effective mite removal rate as high as 96% and suggested that lithium chloride was a highly efficient substance for mite removal. This study aims to investigate the effects of 25 mmol·L－1 lithium chloride on the sucrose sensitivity, learning and memory of honeybees, and provide a reference for the application of lithium chloride as an acaricide for honeybees. [Methods] We used 50%(w/v) sugar water to draw honeybees to the hive entrance . Honeybees foraging for sugar water were caught and considered to be foragers. We randomly divided these honeybees into five treatment groups and one control. In view of the acclimation period of honeybees to a cage environment, control and treatment groups were both fed 30% (w/v) sugar water ad libitum in an incubator at constant temperature and humidity [(30±1)℃, relative humidity 40%±10%, dark] for 24 h (50 bees per box), then fed 30% (w/v) sugar water ad libitum and 30% (w/v) sugar water containing 25 mmol·L－1 lithium chloride ad libitum for 24 h, respectively. Three of the six groups were used to test sensitivity to six different sugar water concentrations (0.1%, 0.3%, 1%, 3%, 10% and 30%), the remaining three groups were used for olfactory-associative learning experiments. Captured foragers were not kept in cages in the laboratory. We randomly divided these bees into control and treatment groups (35 bees per group), both of which received odor-associative learning training. After this bees in both groups were fed 10 μL 30% (w/v) sugar water and 10 μL 30% (w/v) sugar water containing 25 mM lithium chloride. We tested bees’ memory after 2 h, with three replicates. [Results] There was no significant difference in mortality between control and treatment groups within 24 h of lithium chloride treatment (P > 0.05). In the sugar water sensitivity test, the proboscis extension response rate for low concentration sugar water (0.1%-3%) was higher in the treatment group than in the control group (0.3%: P < 0.05; 1%: P < 0.01; 3%: P < 0.001). The sucrose response scores (SRS) of the treatment group were also significantly higher than those of the control group (P < 0. 01). In the olfactory associative learning experiment, the proboscis extension response rate of the two groups increased with training time. The proboscis extension response rate of the control group was significantly higher than that of treatment group (P < 0.05) in the second learning test, but the difference in learning ability between the two groups decreased with training frequency, eventually becoming similar. In the 2 h memory experiment, the proboscis extension response rate of the treatment group was significantly higher than that of the control group (P < 0.05). [Conclusion] 25 mmol·L－1 lithium chloride has no acute lethal effect on honeybees. Exposing honeybees to this concentration of lithium chloride for 24 h enhanced their sensitivity to low concentrations of sugar water. Exposure to 25 mmol·L-1 lithium chloride did not affect the learning behavior of honeybees, but did affect their 2 h short-term memory, which may improve their foraging behavior.