What factor can lead to a decrease in honey bee populations?

Uncontrolled pesticide use is a significant factor that can lead to a decrease in honey bee populations. Pesticides, particularly neonicotinoids and other harmful chemicals, can have detrimental effects on bees' health. These substances may weaken their immune systems, impair their ability to forage and navigate, and can even be lethal upon exposure. Prolonged or excessive use of pesticides in agricultural practices can result in increased mortality rates among bees, reduced reproductive success, and greater vulnerability to diseases and environmental stresses. As a result, districts or farms where pesticides are mismanaged or used thoughtlessly can contribute significantly to the decline of local bee populations, thereby affecting pollination and biodiversity.

The factors like overpopulation within a hive or excessive nectar flow do not directly cause a decline in bee populations; instead, they may lead to other hive management issues. Increased flower variety is generally beneficial, providing bees with diverse food sources, hence encouraging healthy populations.