Honey bees rented to out pollinate crops from apples to watermelons return to their hives with pollen containing an array of agricultural chemicals that make the insects more vulnerable to infection by a lethal parasite, according to a new study.

While other research has shown certain pesticides, including insecticides known as neonicotinoids and others used to fight parasitic mites, can compromise bee health, the new study shines a light on the impact of sprays used to kill fungi and molds.