Cuticular structures on antennae of the bot fly, Portschinskia magnifica (Diptera: Oestridae)

Portschinskia magnifica Pleske, 1926, is an endangered subcutaneous parasitic fly of voles that mimics bumblebees in appearance. Although the importance of antennae in Diptera has been repeatedly stressed, there is still a lack of morphology information of this group, let alone this species. Antennae of adult P. magnifica were studied with a stereoscopic microscope and scanning electron microscope. Six subtypes of antennal sensilla were observed on the funiculus and arista (one subtype of trichoid sensilla, one subtype of basiconic sensilla, and four subtypes of coeloconic sensilla). Sensilla on the antennal funiculus from one sample of both male and female flies were also mapped. Female P. magnifica bear a larger number of sensilla than males, and more sensilla were discovered on the posterior surface than on the anterior surface. However, what make this species special are the distinct structures and new morphological characteristics discovered in the antenna. The antennal funiculus of P. magnifica is completely enveloped by an antennal pedicel. A large number of branched or unbranched trichoid and basiconic sensilla are identified on the antennal funiculus. These two make the most numerous types of sensilla distributed all over the funicular surface. P. magnifica has the most coeloconic sensilla subtypes in previously studied oestrid flies. A total of four subtypes of coeloconic sensilla are found, with subtype I and subtype II on the proximal and middle part of the antennal funiculus and subtype III and subtype IV on the antennal arista. Two large bristles that resemble mechanoreceptors on the proximal two antennal segments located close to the arista are a unique feature. This has never been described in the oestrid funiculus. Interestingly, these bristles can appear as multi-tipped short structures in some individuals. P. magnifica lacks sensory pits that are usually abundant in other oestrid flies. The size, number, and distribution of sensilla on the male and female antennal funiculus are provided here, armed with a discussion of their presumable sensilla functions and evolutionary trends.