Iphiopsid mites are highly regressive dermanyssoid mites that are intimately associated with cockroaches, spiders, terrestrial crustaceans, and myriapods (Halliday 1993; Lindquist et al. 2009). Seven of the 11 genera of Iphiopsidae are associated with millipedes, with the genera Jacobsonia, Julolaelaps, Narceolaelaps and Scissuralaelaps represented by several species each, and Iphiopsis, Iphiolaelaps and Trichaspis being monotypic (Farfan & Klompen 2012).
The only published records of Iphiolaelaps myriapoda are Womersley's (1956) description of an adult male and female collected from “millipedes from Mt Lamington, Queensland, December 1948″, and those reported by Seeman & Nahrung (2000). These mites, however, can be collected readily from paradoxosomatid millipedes (Myriapoda: Polydesmida). The host species in the cover photograph is either Heterocladosoma or Solaenodolichopus, common and beautiful genera found in wet forests around Brisbane, Australia. An undescribed species of Iphiolaelaps occurs on the paradoxosomatid Phyllocladosoma annulatipes (Verhoeff), exhibiting an even greater reduction in sternal shields and the fixed digit compared with I. myriapoda, presumably representing further adaptations to their assumed parasitic lifestyle.
The biology of Iphiopsidae is poorly known. All active life stages of Iphiolaelaps spp. were found on their hosts. The most mites recorded on a single millipede was 59 individuals of the undescribed Iphiolaelaps (36 females, 10 males, 11 nymphs, 2 larvae). When numbers of adults mites were low (< 6 on a millipede), the sex ratio was approximately two-thirds female (20 females, 12 males, 65 ± 11 % female; n = 14 millipedes). With increasing numbers of adult mites, the sex-ratio was more female-biased (92 females, 22 males, 81% ± 5 % female; n = 6). This significant increase (χ21=4.63, P=0.03) in female-bias seems to follow the models of Bulmer and Taylor (1980) and Wilson and Colwell (1981), who predicted greater female bias when more generations were spent in a patch. The less female-biased ratio found on millipedes with few mites (i.e. colonisation is recent) may arise if founding females have control over sex determination, with sons being produced by before daughters (via arrhenotoky or pseudoarrhenotoky). The change in sex ratio bias as populations increase could also occur via differential adult mortality or dispersal. Earlier male emergence (protandry) may also lead to this pattern over time, and enable the precopula described below.
The cover image shows an adult male and deutonymph I. myriapoda in precopula. Pre-copulatory guarding of deutonymphs is common in mites and likely involves arrestant pheromones (Sonenshine 1985). In the Mesostigmata, this behaviour has been recorded in several groups including the Ameroseiidae, Ascidae, Laelapidae, Macrochelidae and Phytoseiidae (Hoy & Smilanick 1979; Yasui 1988; Walter & Proctor 1999; pers. obs.).
In mites, precopula likely favours first-male sperm precedence, i.e., the first male to mate fertilises most or all of the female's eggs (e.g., Yasui 1988). However, in some other animals, such as crustaceans, precopula may also reflect a short period of receptivity by the female. Further, precopula removes the time required to find a mate, which may be critical for species that occupy ephemeral habitats. For example, Hattena panopla Domrow occupies flowers that provide food for just a few days (Seeman 1996), so migrating as a mated female almost immediately after moulting would presumably be advantageous. Additionally, male mites are often seen not only guarding an immature female, but fighting off competing males. Such competition amongst males is commonplace in animals, and is often regarded as a means for females to mate with the fittest suitor.
