Orbuspedum machinator, Gavrilov-Zimin, 2017

Gavrilov-Zimin, I. A., 2017, A remarkable example of symbiosis between an animal and a fungus in a new species of legless mealybug (Insecta: Pseudococcidae), Journal of Natural History 51 (37 - 38), pp. 2211-2224 : 2213-2220

Orbuspedum machinator sp. nov.

( Figures 2–5 )

Material

Holotype, adult female: K 714, southern Thailand, vicinity of the Khao Sok National Park , on twigs of bamboo, 4 November 2010, coll. Ilya Gavrilov-Zimin. Paratypes: 5 adult females with same collection data as holotype, and 1 female with the same data, but collected 19 November 2013 (K 1151), each mounted singly on separate slide.

Additional, non-type material: K 714, two ultimolarvae, same data as holotype, mounted on separate slides . Series of females in ethanol: K 714 and K 1151, same collection data as holotype, but collected 19 November 2013 .

Description

Adult female. Body spindle-form, up to 5 mm long, with posterior segments of abdomen heavily sclerotized. Antennae very short, each 2-segmented, about 50 μm long. Legs entirely absent. Anal apparatus simplified, without setae; anal ring located inside of short anal tube; opening of anal tube at apex of abdomen. Vulva of unusual structure, funnel-shaped, opening directed anteriorly ( Figure 4 ). Both pairs of ostioles absent. Small oval circulus, about 70 μm wide, present. Multilocular pores absent. Trilocular pores (each about 5 μm in diameter) and simple discoidal pores (each about 4 μm in diameter) scattered over entire body surface except posterior abdominal segments, where they are totally absent. Discoidal pores of irregular structure or duct-like pores absent. Tubular ducts, each about 7 μm long, with very deep collar, present on posterior abdominal segments only. Dorsal surface of body covered by small thin conical setae and minute flagellate setae; ventral surface covered by longer flagellate setae; posterior abdominal segments densely covered by significantly longer flagellate setae on both surfaces. Sacciform invaginations of sclerotized cuticle of different sizes present in transverse rows across most segments of body.

Female ultimolarva (probably third immature instar). Body broadly oval, enlarged posteriorly, about 1.5 mm long. Antennae each 2-segmented, very short, about 40 μm long. Legs absent. Anal apparatus located on body surface (without anal tube) at apex of abdomen; structure of anal apparatus rather unusual, with anal opening covered by sclerotized operculum; anal ring with one row of very small poorly visible pores and with four minute setae (see detail in Figure 5 ). Both pairs of ostioles absent. Small round circulus about 20 μm wide present. Multilocular pores, each about 8 μm in diameter, of asteroid form, with one central loculus and 11 peripheral loculi, scattered over entire dorsal surface of body and venter of abdominal segments; occasional pores also present in medial zone of thoracic sternites. Trilocular pores, each about 3 μm in diameter, sparsely scattered over entire body surface. Tubular ducts, each about 5 μm long, same structure as in adult female, few, present in marginal zone of two posterior abdominal segments. Minute flagellate setae sparsely scattered over entire body surface; longer setae present around anal opening. Sacciform invaginations of sclerotized cuticle of different sizes present in transverse rows on abdominal segments.

Males and larvae of other stages unknown.

Etymology

The species name is a masculine Latin word which means ‘constructor’. So, the binomen is translated as ‘legless constructor’, referring to the fungal domicile in which it is found.

Mode of life

The collected adult females and larvae inhabit individual conical domiciles on thin twigs of an undetermined species of bamboo ( Poaceae ). The domiciles are intensely black, each up to 7 mm wide and 8 mm high. In some cases the individual domiciles merge at their bases ( Figure 6 ). Each domicile has a small orifice at the apex, which is used by the encapsulated insect for sprinkling the honeydew. The domicile consists of densely packed hyphae of sooty mould Capnodium sp. (Capnodiaceae) ( Figure 7 ), which are mixed with small portions of wax produced by the mealybug.

Other larval stages of the mealybugs, and males, have not been found. All the studied females contained ovarioles at an early stage of development. Spermatheca and sperm bundles inside the oviducts were not detected. From the vulva, an unpaired oviduct is anteriorly directed proximally, then bifurcates into two thicker paired oviducts distally.

Figures

Figure 2. Orbuspedum machinator gen. et sp. nov.; (a) microscopic characters of the holotype; (b) fungal domiciles with a female inside.

Figure 3. Orbuspedum machinator gen. et sp. nov., photograph of the slide-mounted holotype.

Figure 4. Orbuspedum machinator gen. et sp. nov., photograph of the anteriorly directed vulva and circulus.

Figure 5. Orbuspedum machinator gen. et sp. nov., microscopic characters of the ultimolarva.

Figure 6. Fungal domiciles of Orbuspedum machinator gen. et sp. nov.; (a, b) several merged domiciles on a twig of bamboo; (c) a domicile divided into three parts.

Figure 7. Hyphae of sooty mould under the microscope.