This spring we visited delightful mason bees as they foraged for nectar and pollen to provision their nests inside small cardboard tubes. Tiny bee larvae spent the last several months completing development and are now pupating in their chambers, but all is not well in the realm of mason bees. Enemies are afoot. Several weeks ago, I noticed a gang of noisy yellow and black insects, leucospid wasps, carefully inspecting the modular condominiums of my mason bees. Leucospids are generally considered rare insects, but the tubular homes of the mason bees attracted scads of these parasites. Leucospids are rather unique in the wasp world.
Unlike most of their kin with rear facing or under slung egg-laying tubes called ovipositors, leucospids carry their egg-laying tube arched up and over their back. The small yellow and black wasps moved back and forth across the surface of the mason bee’s tubes tapping them gently with their antennae. This behavior has been noted in other species of leucospids and is likely how the female wasp evaluates the suitability of the mason bee within the tube as a meal for her young.
If the female leucospid likes what she finds, she uses her remarkable ovipositor to drill through the cardboard tube and deposit an egg inside the cell of the developing mason bee. It was fascinating to watch the female wasps drill in and out of the tubes, searching for bees to serve as food for her young. After a few days, the wasp’s eggs hatch into a voracious larvae that consume their mason bee victims. Larvae of the parasitic wasp complete development after a week or so and emerge as adults from the tube to search for more bees.
I pondered the peril of my mason bee colony and soon realized that the majority of my hard working bees would be spared from the treacherous leucospid wasp. When it comes to attacking bee larvae hidden in tubes, size does matter. The ovipositor of the leucospid wasp is only long enough to penetrate the outermost tubes of my modular mason bee condominium. The majority of tubes and mason bees sheltered therein are well beyond the reach of leucospid’s dangerous egg-laying appendage. Next spring after my masons provision their nests and lay eggs, an enclosure of fine netting should further dissuade attack by these pirates of the insect world.
Inspiration for this episode comes from a recent endorsement of mason bees by Martha Stewart. Two interesting articles “Parasitic Behavior of Leucospis cayennensis Westwood (Hymenoptera: Leucospidae) and Rates of Parasitism in Populations of Centris (Heterocentris) analis (Fabricius) (Hymenoptera: Apidae: Centridini)” by Ana Lúcia Gazola and Carlos Alberto Garófalo and “Osmia ribifloris, a Native Bee Species Developed as a Commercially Managed Pollinator of Highbush Blueberry (Hymenoptera:Megachilidae)” by P. F. Torchio were used as references for this episode.