Metal Screen at the Entrance of a Hive does not Affect Production and Reproduction of Honey Bees1 and Can Prevent Predation by Hornets2

Introduced hornets increase natural enemies and stress factors detrimental to honey bees, Apis mellifera L. Hornets are slightly bigger than honey bee drones, the largest member of A. mellifera colonies, offering a possibility of excluding hornets from entering hives because of their larger size. Using screen with an appropriate size of holes allowed free flow of honey bees and may impede the passage of larger predators, including hornets. Metal screens with 0.74 cm holes were installed in eight honey bee hives, using eight colonies without screens for comparison. Colonies with screens produced significantly more honey than did colonies without screens, and no differences were found in the accumulation of pollen or presence of brood between colonies with or without screens. Results indicated the screens were not detrimental to reproduction and honey production by the colonies, but had a beneficial side effect on colony fitness, probably my reducing robbing. Vespa crabro from preserved museum specimens were as small as 0.64 cm at its widest dimension, V. velutina 0.70 cm, while V. mandarinia might not pass through a screen hole smaller than 1.1 cm. Honey bee drones had a maximum metathorax width of 0.6 cm, suggesting that mesh with a hole size slightly larger than 0.60 cm might be appropriate to exclude these hornet species without decreasing productive and reproductive parameters of honey bee colonies.