Brood cell of the European beewolf with two bees, one carrying an egg. Image credit: Gudrun Herzner (CC BY 4.0)
Humans use heat, cooling, and freezing to protect their foods from mold and bacteria. Many animals, including a wasp called the European beewolf, have also developed ways to store and preserve food. Female beewolves hunt honeybees. After paralyzing a bee, the beewolf takes the body into an underground chamber and lays an egg on it. When a larva hatches from the egg, it feeds on the bee. The warm, humid conditions in the chamber provide ideal conditions in which larvae can develop, but also encourage mold and bacteria to grow.
Previous research has uncovered two methods used by beewolves to fight off mold. In 2007, researchers discovered that the female beewolf coats her bee prey with a layer of fats. This prevents water loss and keeps the outside of the bee dry so that mold spores cannot grow. In 2010, a further study showed that the female beewolf grows helpful bacteria inside her antennae and transfers some to her young. The bacteria produce antibiotics that protect the larvae and their cocoons from mold. But these two strategies alone cannot explain the high survival rate of beewolf young. This suggests that the beewolves have at least one more strategy to prevent mold from growing.
Now, Strohm et al. – including some of the researchers involved in the 2007 and 2010 studies – show that beewolf eggs emit high levels of a gas called nitric oxide, which reacts with oxygen to form nitrogen dioxide. Nitrogen dioxide is part of the air pollution generated by cars and is harmful to many species in high concentrations. Nitric oxide also plays an important role for many biochemical processes in virtually all organisms, albeit in very low concentrations. The beewolf eggs produce comparatively huge amounts of this gas to fumigate their brood chambers and protect themselves and their food from mold.
Strom et al. then investigated how the eggs produce nitric oxide. The eggs appear to use the same enzyme that some other organisms use to produce nitric oxide. However, the wasp version of the enzyme contains a small modification that might explain why the eggs can produce the gas in such large amounts.
Learning more about how beewolves evolved different anti-mold strategies could help researchers to develop new antimicrobial treatments for medical applications. In addition, it is not yet clear how the wasp eggs survive in high concentrations of nitric oxide and nitric dioxide. Inflammation and some human diseases produce nitric oxide, killing nearby cells. Understanding how the beewolf eggs survive could therefore help to treat these cells or protect them from damage.
