Two new species of the aphid genus Uroleucon (Hemiptera: Aphididae) living on Grindelia in the USA

Here, we present descriptions of two new aphid species of the genus Uroleucon Mordvilko, 1914 (Hemiptera: Aphididae: Macrosiphini), which are associated with the plant genus Grindelia Willd. (Asteraceae). An apterous viviparous female of Uroleucon (Lambersius) robinsoni sp. nov. from Oregon and apterous and alate viviparous females of Uroleucon (Lambersius) grindeliae sp. nov. from Colorado are described and illustrated. Taxonomical notes of the new and other Grindelia-feeding taxa of Uroleucon are given and an updated key to the apterae of the Grindelia-feeding species of Uroleucon in the world is provided.


Introduction
The genus Uroleucon Mordvilko, 1914, which comprises 239 aphid species in the world, is one of the most speciose genera in the tribe Macrosiphini Wilson, 1910(Favret 2020. The genus has six subgenera: Belochilum Börner, 1932 (one species), Divium Pashtshenko, 2000 (one species), Lambersius Olive, 1965 (53 species), Satula Olive, 1963 (one species), Uroleucon Mordvilko, 1914 (122 species) and Uromelan Mordvilko, 1914 (61 species) (Favret 2020). All of the species live on herbaceous plants that belong to the families Asteraceae (more than 160 species) and Campanulaceae (11 species) without any host alternation; only nine species use host plants from other plant families (Blackman 2010;Blackman & Eastop 2020). The coloration of species of Uroleucon varies from green to blackish brown (Heie 1995;Blackman & Eastop 2020). The genus is generally characterized by well-developed antennal tubercles with diverging inner sides, the presence of secondary rhinaria on the basal part of antennal segment III in apterae, often a very long processus terminalis, ultimate rostral segments with blunt apices, long and cylindrical reticulated siphunculi, a fi nger-shaped cauda with a pointed apex and fi ve setae (a few species have three or four setae) on the fi rst tarsal segments. In many species, the abdominal dorsal setae are located on pigmented scleroites (Blackman & Eastop 2020).
During an examination of the aphid collection in the Natural History Museum of London (BMNH), slides with two undescribed species of Lambersius, which had been sampled on Grindelia hirsutula Hook. & Arn. and G. squarrosa (Pursh) Dunal (Asteraceae) in Oregon and Colorado, respectively, were recognized. In Blackman & Eastop (2006: 496), these species were included in the key to apterae aphids on Grindelia Willd. as "Uroleucon (Lambersius) sp. (on G. stricta DC., Oregon)" and "Uroleucon (Lambersius) sp. (on G. squarrosa, Colorado)". The aim of this paper is to describe these two Grindeliafeeding species of Lambersius from the USA.

Material and methods
The specimens were examined using a Leica DM 3000 LED light microscope and photographed using a Leica MC 190 HD camera. The measurements were taken according to Ilharco & van Harten (1987). The measurements are given in millimeters. The material examined for each species is given in the review of the species. The host plant names are given according to the most recent edition of The Plant List (2013). 1.33 × BASE and 1.18-1.25 × HT II with 7-9 short, fi ne, pointed accessory setae (Fig. 2d); HT I with 5:5:5 setae; SIPH subcylindrical, slightly tapering without a fl ange (Fig. 2e); its reticulated zone 0.17-0.28 × SIPH. SIPH 2.30-2.68 × cauda and 0.31-0.41 × BL; scleroites on setal bases absent on ABD I-V, while setae on ABD VI-VIII arise from barely visible, rounded scleroites; cauda narrow fi nger-shaped without constriction and with 7-9 setae (Fig. 2f).

Etymology
We are very pleased to name the new species in honor of A.G. Robinson  PIGMENTATION OF CLEARED SPECIMENS ON SLIDE. Body generally membranous, pale to yellow; ANT brown with pale ANT I-II and basal part of ANT III; coxae and trochanters pale; femora yellow with light brown distal ends; tibiae brown with paler middle section or pale with only distal part darker; tarsi light brown; SIPH yellow with light brown to brown distal ends; cauda pale ( Fig. 1a).

Remarks
Of the six Grindelia-feeding aphids of Uroleucon, only U. penderum Robinson, 1986, U. robinsoni sp. nov. and U. grindeliae sp. nov. have shared characters: (1) ANT III has the majority of the secondary rhinaria on the basal half and (2)  The apterous viviparous females of the two new species differ from each other in the following characters: (1) their ANT PT/BASE ratio is 4.66-6.50 in U. robinsoni sp. nov., while it is 3.31-3.61 in U. grindeliae sp. nov., (2) their SIPH/CAUDA ratio is 2.30-2.68, while it is 1.37-1.77 in U. grindeliae sp. nov. and (3) their cauda is fi nger shaped with no constriction in U. robinsoni sp. nov. (Fig. 2f), while it is tongue shaped with an evident constriction near the base in U. grindeliae sp. nov. (Fig. 3f).

Biology and distribution
The species was collected from Grindelia squarrosa in Colorado, USA. Other morphs and the life cycle of the new species are unknown.

Etymology
The name of the new species is derived from the host plant genus Grindelia. PIGMENTATION OF CLEARED SPECIMENS ON SLIDE. Body generally yellow to pale brown; ANT yellow with light brown ANT III (very basal part pale) or ANT yellow with darker apices of ANT III-V; coxae and trochanters pale; femora of legs yellow with very distal part light brown or uniformly yellow; tibiae yellow to light brown with slightly darker distal ends; tarsi light brown; SIPH pale to yellow with darker distal half; cauda pale (Fig. 1b).

Alate viviparous female (n = 11) COLOR IN LIFE. Unknown.
PIGMENTATION OF CLEARED SPECIMENS ON SLIDE. Head and thorax slightly sclerotized, pale to pale yellow; ANT yellow with light brown ANT III (except base) and brown basal part of ANT IV; coxae and trochanters pale; femora of legs yellow with very distal ends light; tibiae brown with paler middle section; tarsi yellow to light brown; SIPH yellow to brown with paler bases; cauda pale (Fig. 1c).

Remarks
Of the six Grindelia-feeding aphids of Uroleucon, only U. penderum, U. robinsoni sp. nov. and U. grindeliae sp. nov. have shared characters: (1) ANT III has the majority of the secondary rhinaria on the basal half, (2) their URS/HT II ratio is 1.15 or more and (3) the coxae and trochanters are pale (Robinson 1986;Blackman & Eastop 2020).

Biology and distribution
Representatives of this species live on Grindelia hirsutula in Oregon, USA. Other morphs and the life cycle of the new species are unknown.

Discussion
The subgenus Lambersius is a Nearctic group of yellowish-green or green aphids that have a pale cauda and dark siphunculi with pale or almost pale bases or completely pale siphunculi (Robinson 1986;Heie 1995;Nieto Nafría et al. 2007). Robinson (1986) prepared an annotated list of the species of Lambersius that are known north of Mexico in North America, provided a key for 29 species and described seven new taxa. At present, 26 species of the subgenus Lambersius have been reported from the USA (Blackman & Eastop 2020 (Robinson, 1964) on Grindelia spp. and Viguiera Kunth sp. in Canada, the USA and Mexico (Robinson 1964(Robinson , 1985(Robinson , 1986Nieto Nafría et al. 2007, 2011, 2019Jensen et al. 2010;Blackman & Eastop 2020).
The apterous viviparous females of U. brevisiphon and U. chani have a completely dark SIPH and pale cauda and belong to the subgenus Uroleucon, while the remaining four species have dark siphunculi with pale or almost pale bases or completely pale siphunculi, pale coxae and trochanters and belong to the subgenus Lambersius. Uroleucon brevisiphon is listed in square brackets in the list of Grindeliaassociated aphids as a dubious record (Blackman & Eastop 2020). Two Grindelia-feeding species fi t the diagnosis of the genus Uroleucon well and are members of the genus Lambersius based on the pigmentation of the siphunculi, coxae and trochanters. After our investigation, the number of species of Lambersius increased from 53 to 55 species. It would be interesting to conduct combined morphological, morphometric and molecular (DNA barcoding) investigations of species of the subgenus Lambersius in the future.

Key to the apterae of Uroleucon on Grindelia spp.
Note: the key is modifi ed from that of Blackman & Eastop (2020) (Robinson, 1964 Robinson, 1986 gratefully acknowledges the Scholarship for Outstanding Young Scientists from the Ministry of Science and Higher Education of Poland (1165/E-340/STYP/12/17).