Bees provide crucial pollination services to both cultivated and wild plants. In recent decades there were large declines in the populations of several native bee species and in the health of managed honey bee colonies. Neonicotinoid pesticides were suspected to negatively impact the health of native and managed bees, although this topic was hotly contested. Unfortunately, we lacked the knowledge regarding the typical duration that bees were exposed to neonicotinoids. Therefore, I first quantified the dose, duration, and types of chemicals honey bee colonies were exposed to near agricultural corn fields (Chapter 2). I found that honey bee colonies were exposed to a cocktail of chemicals, out of which neonicotinoids were the most likely to pose a health risk. I also found that honey bees were exposed to neonicotinoids for up to four months the majority of the honey bees active season. I then performed a controlled experiment, where I exposed honey bee colonies to neonicotinoids in a manner that mimicked the field exposure (Chapter 2 and 3). I found that this field realistic exposure to neonicotinoids reduced worker life span, increased queenlessness, and impacted both social and innate immunity. Then, I studied the genetic underpinnings of neonicotinoid sensitivity in honey bees (Chapter 4). I found that survival after neonicotinoid exposure was heritable and was associated with natural polymorphisms found in two detoxification genes. Although survival after exposure is a convenient trait to study under laboratory conditions, it offers little insight into the plethora of phenotypes sublethal neonicotinoid exposure can affect. Thus, I used transcriptomics to look into the effects of field and field realistic exposures to neonicotinoids on the brain gene expression of forager and nurse honey bees (Chapter 5). I found that neonicotinoids affected the brain states of foragers and nurses in a different manner, possibly reflecting a consequence of developmental alterations. I then applied transcriptomics tools to a declining bumble bee, Bombus terricola (Chapter 6). I discovered that bumble bees near agriculture had signatures of stress due to pesticides and pathogens. Overall, I found that neonicotinoids and agricultural landscapes put undue stress on the health of bees. My research also highlights the importance of conducting season-long studies and quantifying multiple stressors and phenotypes at a time in ecotoxicological research.