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What can a 100-million year old fly tell us?

A newly published account of early Cretaceous parasitism in amber.

A newly published account of early Cretaceous parasitism in amber.

Amber is often called 'a window to the past'; it preserves biological inclusions almost intact, providing us with an excellent opportunity not only to study the morphology of extinct organisms in details, but also to understand the biology of ancient animals. Ambers are particularly important for the study of insects, and Archizelmiridae is a good example.

Archizelmiridae is a group of rare, extinct long-horned flies (Nematocera, or lower Diptera), probably related to black fungus gnats (Sciaridae). They have been previously reported from Cretaceous ambers in Lebanon, New Jersey, and Myanmar, as well as the well-known Upper Jurassic locality Karatau in Kazakhstan.

In a recent paper Antonio Arillo, Vladimir Blagoderov, and Enrique Peñalver described another species of these flies from the Lower Cretaceous amber of Spain. It belongs to a genus known from Burmese amber. This makes distribution of archizelmirids continuous in time and space. Of course, the climate in the Cretaceous was very different, with temperatures almost 10° higher in the areas where archizelmirids were found.

More interestingly, one of the flies found has a mite attached. Although these parasitic mites, specialising on various insects, are not particularly rare in Cretaceous ambers, this is only the second time they have been found attached to the host.

Antennae of the three genera of archizelmirids known from amber tell us a remarkable evolutionary story. The oldest, Zelmirarcha, from the Lebanese amber (~121 Mya), has a thread-shaped antenna, typical for many gnats. In Archimelzira, from New Jersey amber, which is 20 million years younger, basal segments of antennae are shortened and expanded, and apical long and thin. Burmazelmira from Myanmar and Spain has basal segments consolidated in a stable but very movable bulb bearing a “whip” formed from a few apical segments. This progressive modification of antennae mirrors the evolution of short-horn flies, or Brachycera (where the most widely known flies, such as horse flies, flower flies, fruit flies, house flies, bluebottles, etc. belong), and helps us to understand how brachyceran antennae evolved.

We do not know much about the biology of archizelmirids, but we could assume that they were better fliers than most of long-horned flies. Modification of antennae not only improved its olfactory function, but made it more mobile, and more useful in stabilising flight. Additional evidence comes from structure of the wing – costalisation of venation (modification of wing when front veins are strong and moved towards wings front margin) makes the wing more aerodynamic and flight more manoeuvrable. No wonder it could fly bearing relatively large and heavy parasite!

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