Mitodiplosis graminis Kieffer

Kolesik, Peter & Wood, Alan R., 2019, Redescription of Mitodiplosis graminis (Diptera: Cecidomyiidae), a gall midge inhibiting the flowering of pyp grass Ehrharta villosa (Poaceae) in South Africa, Zootaxa 4614 (1), pp. 173-179 : 174-178

publication ID	https://doi.org/ 10.11646/zootaxa.4614.1.8
publication LSID	lsid:zoobank.org:pub:501BC4C0-9222-4F4B-B751-70868764FFA9
persistent identifier	https://treatment.plazi.org/id/03A287A3-FF9E-FFDD-FF04-56EEFC8FFB99
treatment provided by	Plazi
scientific name	Mitodiplosis graminis Kieffer
status

Treatment

Mitodiplosis graminis Kieffer View in CoL

( Figs 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 )

Mitodiplosis graminis Kieffer, 1914: 516 View in CoL .

Types. Male and female, reared by Louis Péringuey from an unspecified gall on Ehrharta villosa View in CoL plants collected near Cape Town, South Africa in or before 1914. The types are presumably lost ( Gagné & Jaschhof 2017). We are note designating a neotype as the species is easily recognizable and there is no doubt about its identity.

Other material. 19 males, 3 females, 5 pupal exuviae, 5 female pupae, 6 larvae, collected and reared by Alan R. Wood from stem galls on E. villosa collected near Sedgefield, at the edge of a sandy beach near the mouth of lake Swartvlei (34. 026°S, 22.772°E), Western Cape Province, 22-vi-2018, deposited at ISAM (SAM-DIP-A015535 to SAM-DIP-A015555) and SAMA (29-005719 to 29-005735) GoogleMaps .

Description. In addition to the generic characteristics, the species can be diagnosed by the following.

Adult. Head: clypeus and labrum with no setae, evenly covered with dense, long microtrichia; second palpal segment substantially narrower, 3.5–6.5x longer than first ( Fig. 2h View FIGURE 2 ) with constriction at basal 1/3–1/2. Flagellomere with circumfilar loops 1/15–1/13 x height of total flagellomere length; on dorsal side regular, 1/11–1/ 9x height of flagellomere length ( Figs 2 View FIGURE 2 e–g).

Male. Colour: head black, antennae, legs and terminalia grey, thorax brown, abdomen orangey red. Wing 5.0– 6.2 mm long, 1.8–2.0 mm wide (n=19), length/width ratio 2.6–3.2.

Head. Antenna: scape widened distally, longer than pedicel, pedicel uniformly wide, shorter than wide ( Fig. 2a View FIGURE 2 ); first and second flagellomere separated; flagellomere ( Figs 2e, f View FIGURE 2 ) with basal node slightly longer than wide, internode and neck slightly shorter than basal node, distal node twice as long as wide, of uniform width.

Thorax. Wing ( Fig. 2i View FIGURE 2 ) with rudimentary R S positioned half way between arculus and distal end of R 1. Scutum and scutellum covered with dense, long microtichia. Tarsal claws: simple on all legs; dark at distal 1/3; straight at basal ¾, slightly bent and abruptly pointed at distal ¼; empodium 1.5 times longer than tarsal claws ( Figs 2j, k View FIGURE 2 ). First tarsal segment without ventro-apical spur ( Fig. 2m View FIGURE 2 ).

Abdomen. Sclerites entire, rectangular, with trichoid sensilla close to anterior margin. Sternites 2–8 with setae sparse, loosely arranged in anterior, medial, posterior and lateral bands. Tergites 1–8 with sparse setae evenly distributed through sclerite. Terminalia ( Figs 2 View FIGURE 2 b–d): gonostyle setulose at basal 1/3 dorsally and ventrally, dorso-distal claw ¼ length gonostyle length; ventro-distal area of gonostyle opposite distal claw covered with dense field of short setae; aedeagus slightly shorter than gonocoxite, substantially longer than cerci, slightly tapering distally, with two parallel rows of 12–16 asetose apical sensoria dorsally and ventrally; hypoproct ( Fig. 2d View FIGURE 2 ) nearly as long as cerci, blunt posteriorly, with small postero-lateral lobe on either side, as long as cerci, with several setae distally.

Female. Wing 6.2 mm long (n=1, wings in remaining two females folded), 2.1 mm wide), length/width ratio 3.0. Flagellomere ( Fig. 2g View FIGURE 2 ): node 3.5 times as long as wide, 7 times as long as neck. Terminalia ( Figs 2l, n View FIGURE 2 ): cerci slightly longer than wide, hypoproct twice as wide as long in dorsal view, 3 times shorter than cerci. Otherwise as in male.

Pupa. Colour of exuviae: anterior part brown, posterior grey; with adult present inside: abdomen red, remaining parts black ( Fig. 1b View FIGURE 1 ). Length 5.8–6.2 mm (n=5). Antennal base with large acute horn ventrally and small round, double-peaked horn dorsally ( Fig. 3a View FIGURE 3 ). Facial horn cylindrical, 1.5 times wider than high ( Fig. 3b View FIGURE 3 ), surface pebbled ( Figs 3a, d View FIGURE 3 ). Prothoracic spiracle strongly tapering, 3 times longer than wide at base, trachea ending at apex ( Fig. 3c View FIGURE 3 ). Abdominal spiracles sessile.

Larva. Colour orangey red. Length 4.0– 5.3 mm (n=6). Head ( Figs 3f, g View FIGURE 3 ): capsule trapezoid in ventral and triangular in anterior view; postero-lateral apodemes not present; length of first antennal segment about ¼ of second, second small, as wide as long. Sternal spatula with two robust, pointed posterior teeth, dividend by deep V-shaped incision; shaft narrowed at anterior end, 2.5 times longer than teeth ( Fig. 3h View FIGURE 3 ). Anus ventral ( Fig. 3e View FIGURE 3 ). No papillae visible on body.

Egg. Elongate, rounded at both ends ( Fig. 3i View FIGURE 3 ). Length 0.55–0.61 mm (n=5), width (0.14–0.17), length/width ratio 3.3–4.2.

Remarks. Cecidomyiidae are rather small insects and the wing length of most of them is 1.5–3.5 mm. With a wing length of up to 6.2 mm, M. graminis is one of the largest species of the family. Interestingly, we know of another sizeable South African gall midge-an undescribed species causing bud galls on Combretum spp. that has a wing length of 8.6 mm (Stefan Neser pers. comm.).

Biology. Mitodiplosis graminis induces a stem gall on Ehrharta villosa ( Fig. 1 View FIGURE 1 ). The leaf blades on an infested stem become shortened, the stem internodes do not lengthen, and the leaf sheaths are thickened and widened, creating a witch’s broom-like structure ( Figs 1a, c View FIGURE 1 ). The superficial tissue layers of the gall (i.e. malformed leaf sheaths and blades) become grey and senescent while the internal tissue (i.e. malformed stem) stays soft and green ( Fig. 1c View FIGURE 1 ). There are 2– 20 larvae, and later pupae, inside separate larval chambers within the malformed stem tissue ( Fig. 1b View FIGURE 1 ). Galls with more larvae are longer than those with fewer larvae. The malformed stem eventually grows out so that it protrudes from the leaf sheaths ( Fig. 1c View FIGURE 1 ) enabling an unhindered emergence of the gall midge from the stem’s surface ( Fig. 1d View FIGURE 1 ). Ehrharta villosa produces long underground stolons with numerous stems per plant. At Sedgefield (Western Cape, South Africa) in 2018, only few stems per ground area were infested by M. graminis , with about 50–100% galls being parasitised by a platygastrid and possibly also by other parasitic wasps. Interestingly, a few empty larval chambers of M. graminis were found to be occupied by Anguina woodi , a large, host specific, gall forming nematode. The nematode is an autonomous gall producer ( Swart et al. 2004) and it seems unlikely that it is involved in a mutualistic relationship with the gall midge, as is found between the nematodes of the genus Fergusobia (Sphaerularioidea: Tylenchida : Neotylenchidae ) and the gall flies of the genus Fergusonina ( Diptera : Fergusoninidae ) in Australasia (e.g. Taylor & Davies 2010).

Geographical distribution. Ehrharta villosa occurs on sand dunes or sandy soils in the proximity of the sea in the Western Cape and the Eastern Cape provinces of South Africa. The area between the seven localities at which M. graminis has been found thus far covers most of the plant’s distribution in the Western Cape province. Louis A. Peringuey discovered the galls from which he reared the type male and female (now presumably lost) near Cape Town in or before 1914. Alan R. Wood found galls and larvae and reared pupae, males and females from plants collected near Sedgefield (34. 026°S, 22.772°E), Western Cape Province, on 22-vi-2018 ( Figs 1 View FIGURE 1 b–d), and galls at Agulhas National Park (34.814°S, 19.941°E) on 3-ii-2014 (emergence completed before this day), Blouberg GoogleMaps beach Cape Town (33.751°S, 18.442°E) on 18-vii-2018 and Milnerton Beach GoogleMaps , Cape Town (33.845°S, 18.488°E) in x- 2002. Jan-Hendrik Keet found galls at Koude Vlakte Nature Conservancy (34. 478°S, 19.457°E), south of Stanford GoogleMaps , Western Cape Province, 150 km south east of Cape Town, on 7-ii-2016 ( Fig. 1a View FIGURE 1 ). Netta Dorchin found galls that contained pupae at West Coast National Park GoogleMaps (33.121°S, 18.067°E), Western Cape Province, 120 km north of Cape Town, on 26-ix-2018. It is to be ascertained if the gall midge occurs also in the remaining part of E. villosa natural distribution range, namely in the Eastern Cape province.