Biology of Hormosianoetus mallotae (Histiostomatidae: Astigmata), a mite restricted to water-filled treeholes

Water-filled treeholes are in reality tiny ponds in the woodland ecosystem and provide a unique habitat for a number of different organisms that make up the treehole community. The community is a detritus based system that relies primarily on decomposing leaves from the autumn leaf drop as an energy source. Among the arthropod inquilines is a histiostomatid mite, Hormosianoetus mallotae, an obligate inhabitant that filters microorganisms and other organic matter from the fluid. While larvae, protonymphs, tritonymphs and adults are found in the treeholes throughout the year, deutonymphs are present only in May and June when conditions are optimal for population growth by the treehole residents. Deutonymphs therefore do not form in response to adverse conditions, but rather to serve purely as dispersal agents for colonizing new treeholes and for out-crossing among populations. Deutonymphs are phoretic on another obligate treehole inhabitant, species in the syrphid fly genus Mallota that are also found as adults only during that same time of year. Hormosianoetus mallotae is arrhenotokous and disperses only as female deutonymphs, dispersants mating with their haploid male offspring. Females are ovoviviparous, retaining eggs in the reproductive system during embryonic development and giving birth to fully formed larvae. Development from egg to adult is approximately 14 days for males and 20 days for females. Like other mite inhabitants of the treehole community, H. mallotae is a K-selected species.