I guess I’m getting giddy from too much time humped over a computer or a microscope and a lack of sun and warmth (it’s a cold, late spring here in Alberta). So here is something from a sunnier clime, or rather somethings. The Bemisia whitefly in this image was sent to me by some colleagues in Toowoomba, Queensland (currently with a clear 8C autumn night and a weekend with predicted highs of 23 C, beating the May Long Weekend in Edmonton by 4-5 degrees). Unfortunately, the whitefly was not covered with parasites, but with the infamous Broad Mite Polyphagotarsonemus latus (Banks) (Prostigmata: Tarsonemidae), a plant pest with, as you might guess from the generic name, a broad host range. However, I think the common name comes from it being rather tubby (0.17 x 0.10 mm).
Like many mites, the life history of the Broad Mite is amazing. For one thing, they have reduced their life cycle to the almost the bare minimum – egg, larva, adult – cutting out all three nymphal stages. At a constant temperature of 27 C, this mite can go through a complete generation, egg to egg, in 3 days and summer generation times in the field are typically 4-5 days. As the larvae and adults feed, they distort leaf tissue into folds and bumps that protects them from weather and predators – not quite as fancy as the gall mites in the Eriophyoidea, but on their way there.
Male Broad Mites have a large sucker-like genital capsule sticking out their rear end and they use this to hold onto inactive larvae – pharate females that are finishing up their development within the larval skin. This looks a bit strange – the pharate female crosses the male T – and has fooled several entomologists into thinking they were observing an act of predation. Nope, just males that want to make sure they alone go on a female’s first date. This type of precopulatory guarding has evolved numerous times within the Acari, and in this case is associated with a male aedeagus and a female secondary sperm transfer system. This makes quite a contrast to the oribatid mites with which I am currently working. Male oribatids wander around depositing spermatophores on the substrate wherever they feel like it, whether or not females are around, and make no effort to contact, let alone guard, a female. Perhaps that is one reason that 10% of oribatid mite species appear to be thelytokous (i.e. all female and parthenogenetic).
As you may know, whiteflies are rather small, but not so small that a heap of broad mites can’t hitch a ride. Mites lack wings, so if they want to get between patchy habitats, they have to come up with an alternative means of transportation. A surprising number, including many members of the Broad Mite’s family (Tarsonemidae), simply orient to a stiff breeze and let go to become part of the aerial plankton. That seems pretty inefficient if you have a specific place you’d really like to get before you dehydrate or starve, but I don’t know that climbing on such a tiny and seemingly inefficient flier as a whitefly is much better.