What suppresses the ovaries of worker bees?

The presence of a viable queen's pheromones is the correct answer because these pheromones play a critical role in maintaining the social structure of the hive and regulating the reproductive functions of worker bees. Queens emit specific chemical signals that inform workers of their presence, health, and reproductive status. These pheromones effectively suppress the development of the workers' ovaries, ensuring that the queen remains the primary reproductive individual within the colony. This suppression of ovary development promotes colony stability and efficiency by allowing workers to focus on foraging, nursing, and other essential tasks rather than engaging in reproduction.

The other options do not significantly impact the reproductive capacity of worker bees in the same way as the queen's pheromones do. Cold temperatures may affect the bees' activity and behavior but do not directly suppress ovaries. Similarly, while the absence of nectar can influence food sources and overall hive health, it does not specifically target worker bee reproduction. Lastly, the presence of drones is indicative of potential mating opportunities but does not influence the hormonal environment of the worker bees like the queen's pheromones do.