A new invasive weed-feeding species of Polypedilum ( Pentapedilum ) Kieffer from South Africa ( Diptera : Chironomidae , Chironominae )

Polypedilum (Pentapedilum) tuburcinatum Andersen et Bello González sp. n. is described and figured as male, female, pupa and larva based on material collected in the Eastern Cape Province in South Africa, imported into quarantine in Ireland and reared in the laboratory. The species feeds on the aquatic weed Lagarosiphon major (Ridl.) Moss ex Wager and is regarded as a promising candidate agent for biological control of this invasive weed.


Introduction
The African curly waterweed, Lagarosiphon major (Ridl.)Moss ex Wager (Hydrocharitaceae), has become invasive in freshwater habitats in Europe and elsewhere in the world such as New Zealand and infestation of this submersed plant induces changes to native macrophyte, invertebrate and fish communities (e.g.Howard-Williams & Davies 1988;Bickel & Closs 2008;Hussner 2012).A native of southern Africa, L. major is a potential target for biological control and biological studies on an undescribed Polypedilum species found to mine the plant's shoot tips in its native range have been conducted (Earle et al. 2013).A population of the midge was imported into quarantine in Ireland and reared in the laboratory.Below we describe the species based on males, females, pupae and larvae from this laboratory culture and place it in the subgenus Pentapedilum Kieffer, 1913. Polypedilum Kieffer, 1912 is the most species rich genus of Chironomidae, with more than 440 described species worldwide.Nine subgenera are generally recognized, of which eight occur in the Afrotropical Region: Cerobregma Saether et Sundal, 1999;Kribionympha Kieffer, 1921;Pentapedilum;Probolum Andersen et Saether, 2010;Tripedilum Kieffer, 1921;Tripodura Townes, 1945;Uresipedilum Oyewo et Saether, 1998 and Polypedilum sensu stricto; only Asheum Sublette et Sublette, 1983 has not been recorded from the region (see Saether et al. 2010;Epler et al. 2013).A total of nearly 90 named Polypedilum species are currently recorded from the Afrotropical Region (Saether & Sundal 1999;Vårdal et al. 2002;Oyewo & Saether 2008;Saether et al. 2010;Cranston 2014), of which 10 are assigned to subgenus Pentapedilum.A world revision of the subgenus was published by Oyewo and Saether (2008).Later, Tang et al. (2014) have described the immature stages of Pentapedilum nodosum (Johannsen, 1932) and Pinho et al. (2015) have published a new species from Brazil.
Polypedilum larvae occur in virtually all standing and flowing waters with the exception of the high arctic and high mountains (Epler et al. 2013).Most species prefer sediments, but some are found on hard substrata and some feed on healthy tissues of water plants.A few species are also specialising in plant-held waters (phytotelmata) (e.g.Pinho et al. 2013).Polypedilum (Po.) vanderplanki Hinton, 1951 is known to inhabit temporal pools and can remain desiccated for years (e.g.Kikawada et al. 2005).A second inferred desiccation tolerant species, P. (Po.) ovahimba Cranston, 2014, has recently been described in all stages from rock-pools on the Waterberg Plateau, Namibia (Cranston 2014).

Material and methods
The field surveys and laboratory cultures are described in detail in Earle et al. (2013).The specimens examined were preserved in alcohol and later mounted on slides in Canada balsam following the procedure outlined by Saether (1969).The general terminology follows Saether (1980).The measurements are given as ranges, followed by the mean when more than three specimens were measured, followed by the number of specimens measured (n) in parenthesis.
The holotype and most paratypes are deposited in the Department of Natural History, University Museum of Bergen, Bergen, Norway (ZMBN Etymology.From Latin tuburcinatus meaning eats greedily, referring to the species feeding on the aquatic weed Lagarosiphon major (Ridl.)Moss ex Wager.
Diagnostic characters.The male can be separated from other Pentapedilum species with the following combination of features: more than 100 setae in each of cells m 1+2 and r 4+5 , less than 6 setae in cell m basal of RM, fore tibial scale without spur, base of superior volsella with microtrichia and apical seta of the inferior volsella prominent, reaching apex of gonostylus by having an AR of about 0.8 and more than 10 setae on scutellum.The female can be separated from other known females with the following combination of features: unbanded abdomen, spherical seminal capsules and broadly triangular postgenital plate by having a ventrolateral lobe without brush.However, both sexes can easily be separated from all other described Pentapedilum species on the short fifth palpomere; in both sexes the ratio fifth palpomere / third palpomere is < 1.0, while in all other species this ratio is > 1.0.The pupa can be separated from other known pupae with the following combination of features: strong anterior band of spinules and median and posterior shagreen on tergite II, anterolateral spinules on tergite VII, conjunctive III/IV with spinules and pedes spurii B on segment II comparatively well developed by having about 100 μm long frontal setae and anterolateral patches of spinules on tergite VIII.The larva can be separated from other known larvae with the following combination of features: mandible with dorsal tooth, mentum with median teeth slightly longer than second lateral teeth, and third antennal segment slightly shorter than fourth as the combined length of third and fourth antennal segment is subequal to second segment by having minute Lauterborn organs.
Coloration.In Canada balsam, head, thorax, legs and abdomen brown; wing membrane light brownish.According to Earle et al. (2013) live adults have light brown thorax and green abdomen.
Coloration.Head capsule brown with teeth of mentum and mandible dark brown, postoccipital margin blackish brown.

Remarks
The male of P. (Pe.) tuburcinatum n. sp. is similar to P. (Pe.) camposense Oyewo et Saether, 2008 from Brazil in having wings with just over 100 setae in each of cells m 1+2 and r 4+5 , few setae in cell m basal of RM, fore tibial scale without spur, base of superior volsella with microtrichia, apical seta of the inferior volsella prominent reaching apex of gonostylus, tergite IX with about 10 median setae and the anal point narrow, gradually tapering to nearly parallel-sided.However, the two species are easily separated as the new species has an AR of about 0.8 while the AR in P. (Pe.) camposense is 1.35.Further, P. (Pe.) camposense has only 5 setae on scutellum, while the new species has more than 10 setae in partly double row; the apical portion of the superior volsella appears to be more curved with a much shorter dorsolateral setae than in the new species; and the inferior volsella apparently lacks setae with split apices.
Unfortunately the female and immatures of P. (Pe.) camposense are not known.In the key to the females of Polypedilum subgenus Pentapedilum (Oyewo & Saether 2008) the female of P. (Pe.) tuburcinatum n. sp. will key to P. (Pe.) chutteri Harrison, 2001 from South Africa as the abdomen is not banded, the seminal capsule is spherical and the postgenital plate is broadly triangular.However, the two species can easily be separated as P. (Pe.) chutteri has a brush-like ventrolateral lobe, while the ventrolateral lobe in the new species lacks a brush.Further, the ratio fifth palpomere / third palpomere is about 0.78 in the female of the new species, while it is 1.22 in the female of P. (Pe.) chutteri.
In the key to the pupae of Polypedilum subgenus Pentapedilum (Oyewo & Saether 2008) the pupa of the new species will key to couplet 9 as tergite II has median and posterior shagreen, conjunctive III/IV with spinules and tergite VII has anterolateral spinules, but not further as tergite VIII also has anterolateral spinules.
In the key to the larvae of Polypedilum subgenus Pentapedilum (Oyewo & Saether 2008) the larva will key to couplet 7 as the mandible has a dorsal tooth, the median teeth of mentum is slightly longer than second lateral teeth and third antennal segment is slightly shorter than fourth segment, but no further as the combined length of third and fourth antennal segment is subequal to second segment and Lauterborn organs are minute.

Biology
The larvae of P. (Pe.) tuburcinatum n. sp.feed on actively growing shoots of the submerged aquatic plant Lagarosiphon major.After emerging from a gelatinous egg mass larvae disperse in the water column and settle on plant material.Early larval stages seek out and enter the meristematic tissue in the crown of shoots feeding on the developing leaves and stems.Feeding damage typically stops shoot growth promoting the development of side shoots (Earle et al. 2013), which are equally suitable to the larvae.The larva may move between shoots to complete development and the later instars tunnel a few centimeters and pupate within the stem.The adult female typically deposits one or two egg masses into the water within 2-3 days of emerging.The life cycle takes approximately 30 to 50 days from egg to adult, at water temperatures of ~21ºC (Earle et al. 2013).In the introduced range L. major spreads and competes with native macrophytes only through vegetative growth and requires repeated mechanical control to prevent the formation of large monocultures (Caffrey et al. 2011).By feeding on the new shoots the chironomid has the potential as a candidate biocontrol agent (see Baars 2011) to reduce the growth rate and architecture of L. major if it was to be found safe for a field release in Europe.