The processes of iron deposition in the common hornet (vespa affinis)

Among insects, only honeybees and bumblebees deposit iron biominerals intracellularly. Although hornetʹs behaviour is affected by the magnetic field and their abdomen has magnetic remanence, it is not known whether hornets (Vespa affinis) deposit iron biominerals and whether the process of iron deposition in hornets is the same as that of honeybees and bumblebees. Transmission electron microscopy and atomic emission spectroscopy were employed to study intracellular iron deposition in hornets. Iron deposition began on day 2 after eclosion. Primary iron-granules (IGs) are first formed in primary iron deposition vesicles (IDVs) by the aggregation of tiny dense particles. Primary IDVs are double membrane vesicles that seem to derive from endoplasmic reticulum (ER). Primary IGs enlarged continuously into IGs by the aggregation of tiny dense particles till day 5 after eclosion. Next, IGs and IDVs fused to enlarge on day 7. Between days 10 and 17 IGs enlarged continuously in size by the aggregation of tiny dense particles. The cloudy area beneath the inner membrane of IDVs plays an important role in the formation of the tiny dense particles. IGs became mature on day 25 and left a small space, about 10nm in width, between IGs and the outer membrane of IDVs. IDVs including IGs are randomly distributed within the cytoplasm of trophocytes beneath the cuticle of hornets. Elemental composition analysis indicates that IGs are mainly comprised of iron, phosphorus and minor amounts of calcium.