Every year, billions of pounds of pesticides are used worldwide for agricultural purposes. These chemicals have been shown to cause lethal effects on insects like the honey bee (Apis mellifera). Two commonly used pesticides produced are imidacloprid and carbaryl. The honey bee is a model of plasticity of brain structure; these insecticides physically change the structure of the neurons in their brain. This phenomenon has been most widely studied in the mushroom body, an area responsible for olfactory learning and memory. The effects of pesticides on the Apis brain have been studied using immunohistochemical techniques describing changes of the mushroom bodies’ synaptic structures (so-called microglomeruli). Exploring the effects of concurrent exposure to multiple pesticides is far less common. We visualized and quantified the effects of imidacloprid, carbaryl, and the combination of both in the honey bee brain. Newly emerged honey bees were caged for either a 7-day or 21-day period and fed sugar syrup and a nutritional supplement, each dosed with pesticides. An image analysis program was used to measure the area and amount of microglomeruli in each treatment group. The results suggest that honey bees exposed to pesticides have a decreased microglomeruli density compared to a control group. Additionally, as the bees aged a decrease in density was also observed, even in the control group. These results correlate with others from the lab suggesting that pesticide exposure is linked to a decrease in olfactory learning in Apis, which would likely lead to issues with survival in the wild. 

For more information: erstoner@eckerd.edu