Williamsrhizoecus Kozár & Konczné Benedicty, 2007: 354

Schneider, Scott A. & Lapolla, John S., 2020, Trophobiosis between a new species of Williamsrhizoecus (Hemiptera: Coccomorpha: Rhizoecidae) and Acropyga silvestrii (Hymenoptera: Formicidae) in Tanzania, Zootaxa 4853 (2), pp. 283-291 : 285

Williamsrhizoecus Kozár & Konczné Benedicty, 2007: 354 .

(Type species: Williamsrhizoecus baskyi , by monotypy.)

Checklist of species placed in Williamsrhizoecus

Williamsrhizoecus baskyi Kozár & Konczné Benedicty, 2007: 355 .

Williamsrhizoecus coffeae Caballero & Ramos, 2018: 3 .

Williamsrhizoecus epicopus ( Williams, 1970) : 155.

Williamsrhizoecus udzungwensis sp. n.

Generic diagnosis. Body elongate oval. Antennae each with 5 or 6 segments; with 1 blunt sensory seta situated on penultimate antennal segment. Legs well developed. Dorsum and venter with trilocular pores. Multilocular disc pores present or absent. Oral collar tubular ducts absent. Tritubular pores present on dorsum and venter. With flagellate and clavate or falcate setae present on body surface, anal ring, legs, and antennae in varying combinations. Anal ring with oval to elongate pores, some with spicules, and 6–18 flagellate or clavate setae. Dorsal ostioles entirely absent, or only weakly developed if present. Circuli present or absent.

Comments. Following Kozár & Konczné Benedicty (2007), this genus belongs to the subtribe Rhizoecina based on the presence of tritubular pores; the presence of clavate body setae distinguishes this genus from the others in the subtribe. Note, however, that the study of adult male morphology by Hodgson (2012) found little support for the subdivisions of Rhizoecini (now Rhizoecidae ) proposed by Kozár & Konczné Benedicty. This casts some doubt on their decision to separate Ripersiellina from Rhizoecina , which was based on adult females having either bitubular or tritubular pores, respectively. The possession of blunt sensory setae on the penultimate antennal segment is not diagnostic for this genus, as originally described ( Kozár & Konczné Benedicty 2007), as this feature is common throughout the family.

The description of Williamsrhizoecus is here updated from the original account ( Kozár & Konczné Benedicty 2007) to accommodate recent additions of species, including W. coffeae and the new species described here. The genus now includes species with 5 or 6-segmented antennae (originally 5-segmented only), with or without circuli (originally described as present), with or without multilocular disc pores (originally described as absent), with anal ring cells oval to elongate (originally described as elongate), and with 6–18 anal ring setae (originally described as having 6 setae). Caballero & Ramos-Portilla (2018) implied several of these changes when they described W. coffeae , but they did not explicitly revise the genus.

The absence of dorsal ostioles is a rare, notable trait shared by all but one of the species comprising this genus. However, synapomorphies based on the absence of features are more equivocal than those based on presence. Kozár & Konczné Benedicty apparently regarded the presence of clavate setae on the anal ring as more critical to diagnosis, since they chose to recombine Neorhizoecus epicopus Williams into Williamsrhizoecus based on this trait, despite it being the only member of the genus to possess (weakly developed) dorsal ostioles.

Williamsrhizoecus is evidently Gondwanan in origin, drawing on the known geographical distribution of the few species that comprise it, which includes Antigua and Barbuda, Colombia, Mexico, Tanzania, and Trinidad and Tobago. The rather disjunct distribution of species may reflect that root mealybugs are generally under-sampled, particularly in the Afrotropical region where only 33 out of 216 total species have been recorded ( García Morales et al. 2016; last accessed 13.viii.2020). It could also indicate artificiality of the genus, but this question would be best resolved with molecular evidence and morphological data from additional life stages that are unavailable at present.