Chaetotaxy — Fronto-orbital Setae & Frontal Setae
The frons (postfrons) is the section of the head bounded by the eyes between antennae insertions and the ocelli. On each side of the frons against the eyes lies a schlerotized fronto-orbital plate with the unsclerotized zone outside of the plates called the frontal vitta (Fig. 1). The fronto-orbital plates can be entire along the frons to being absent anteriorly, or sometimes is cut into upper and lower portions. Setae on the fronto-orbital plates are called fronto-orbital setae, or just orbital setae, while setae on the frontal vittae are called frontal setae (e.g. Fig. 5).
Fronto-orbital Setae — Orientation
The orientation of fronto-orbital setae is described as lateroclinate when directed outwards over the eye, inclinate when curved inwards over the frontal vitta, reclinate when curved backwards, and proclinate when curved forwards (Fig. 1). In Acalyptratae the presence of lateroclinate, inclinate or proclinate fronto-orbital setae helps narrow family or genus for certain groups.
Acalyptratae – Lateroclinate Fronto-orbital Setae
Acalyptratae families with members largely showing lateroclinate fronto-orbital setae includes Canacidae (Fig. 2a), Milichiidae (Fig. 2b) and Sphaeroceridae. Ephydridae (Fig. 2c) also has many genera and, for Australia, Apotropina (Fig. 2d) is a notable atypical Chloropidae genus with lateroclinate fronto-orbital setae. When present, strong lateroclinate fronto-orbital setae are typically found in the upper region of the frons.
 |  |
Acalyptratae – Inclinate Frontal and Fronto-orbital Setae
Most Milichiidae (Fig. 2b) and all of Tephritidae (Fig. 3a) have inclinate frontal setae anteriorly on the frons — in these two families the orbital plates are restricted to the upper half of the frons, thus the inclinate setae arise from the frontal vitta. Inclinate fronto-orbital setae are found anteriorly on the frons in most Agromyzidae (Fig. 3b) and, for Australia, in the obscure Australimyzidae and many Clussidae (Fig. 3d) and some Lauxaniidae (Fig. 3c).
Acalyptratae – Proclinate Fronto-orbital Setae
Proclinate fronto-orbital setae are less common among the Acalyptratae, though are generally present for Drosophilidae (Fig. 4d) and many Ephydridae (Figs 4a-b) — for both families often their position and size relative to the reclinate fronto-orbital setae are of great taxonomic importance. For Australia, other notable Acalyptratae groups with proclinate fronto-orbital setae include Neminidae (Fig. 4c) and Apotropina (Chloropidae) (Fig. 2d).
 |  |
Calyptratae – Proclinate Fronto-orbital Setae
Proclinate orbital setae are quite common in Calyptratae, typically for females (Fig. 5), often absent for males. In certain groups where males cannot be recognised by a holoptic state (i.e. eyes not closely approximated), the males can be recognised by the absence of proclinate fronto-orbital setae. This is true for some well-known calyptrate taxa, including Cylindromyiini (Tachinidae) and most Sarcophaginae (Sarcophagidae)(Figs 7c-d)(for Australian Sarcophaginae, only Tricharaea brevicornis has males with proclinate orbital setae) and the iconic tachinid genera Trigonospila (Fig. 6) and Microtropesa (Figs 7a-b).
Alternatively, well known Calyptratae taxa where both sexes have similar fronto-orbital and/or frontal setae include Miltogrammatinae (Sarcophagidae), Siphonini (Tachinidae), and Phasiini (Tachinidae).
 |  |
 |