Macrosiphum aetheocornum Smith and Knowlton, 1939

Jensen, Andrew S., 2022, A new species of Macrosiphum (Hemiptera: Aphididae) living on Silene (Caryophyllaceae), Zootaxa 5183 (1), pp. 75-89 : 85-88

Macrosiphum aetheocornum Smith and Knowlton, 1939

Macrosiphum aetheocornum Smith and Knowlton 1939: 211 ; Knowlton 1940: 197; Palmer 1952: 289; Eastop and Hille Ris Lambers 1976: 255; Smith and Parron 1978: 177; Remaudière and Remaudière 1997: 113; Blackman and Eastop 2006: 1206.

Initial morphological studies of M. ginajo revealed that it is very similar to M. aetheocornum . The two species also share much of their geographical ranges, and both live on sticky–glandular host plants. Therefore, a thorough morphological analysis of M. aetheocornum was undertaken in conjunction with the description of M. ginajo .

Material examined for measurements in Tables 3–4 (all collected by the author in the U.S.A.). CALIFORNIA: AJ 8708, Modoc County, Modoc National Forest, Warners – Summit Trail, ex Geranium , 23 July 2016 (2 ap, 1 al); COLORADO: AJ 9797, Ouray County, Canyon Creek Rd. near Ouray, ex Geranium richardsonii , 29 September 2017 (2 o, 1 am); AJ 5894, Pitkin County, McClure Pass, ex Geranium , 19 August 2012 (2 ap); IDAHO: AJ 6517, Boise County, Boise National Forest, Ridge Rd., ex Geranium richardsonii , 5 July 2017 (2 ap, 2 al); AJ 5832, Fremont County, Bishop Mt., ex Geranium richardsonii , 1 August 2012 (4 ap); AJ 6763, Boise County, Bogus Basin ski area, ex Geranium richardsonii , 31 August 2013 (2 ap); AJ 6547, Bonneville County, Hwy. 31 to Victor, ex Geranium richardsonii , 26 July 2013 (1 ap); MONTANA: AJ 4538, AJ 4539, Ravalli County, Bitterroot River, ex Geranium , 29 August 2010 (4 ap, 1 al); NEW MEXICO, AJ 4657, AJ 4658, AJ 4659, AJ 4660, Sandoval County, Santa Fe National Forest, S. of La Cueva, ex Geranium richardsonii , 25 September 2010 (8 ap, 2 o, 3 am); AJ 4429, AJ 4430, Sandoval County, Valles Caldera, Sulfur Springs Rd., ex Geranium richardsonii , 24 September 2010 (2 ap, 4 o); OREGON: AJ 6418, Grant County, Hwy 26 near Austin Jct., ex Geranium richardsonii , 14 June 2013 (1 ap, 2 al); AJ 9295, Grant County, Hwy 395 milepost 9C S. of John Day, ex Geranium richardsonii , 23 June 2017 (2 ap, 1 al); AJ 8492, Lake County, Warner Mts., Can Spring, ex Geranium richardsonii , 11 June 2016 (2 f); Lake County, Fremont National Forest, near pipeline, Warners, ex Geranium richardsonii , 7 August 2020 (2 ap); AJ 12223, Lake County, Fremont National Forest, Rd. 28, mile post 77, ex Geranium richardsonii , 21 August 2020 (1 ap); AJ 10900, AJ 10901, Lake County, Slope above Lake Abert, ex Geranium viscosissimum , 19 May 2019 (2 ap, 1 al); AJ 10619 Lake County, S. Warner Mts., Dismal Swamp area, ex Geranium viscosissimum , 11 August 2018 (1 ap); AJ 10574, Lake County, Slope Above Lake Abert, ex Geranium viscosissimum , 22 July 2018 (4 ap, 1 al); AJ 9270, Lake County, West side of Lakeview valley, ex Geranium viscosissimum , 10 June 2017 (2 ap, 2 al); AJ 8800, Lake County, Warners near Rogger Meadow, ex Geranium richardsonii , 7 August 2016 (3 ap, 1 al); AJ 11064, Lake County, Fremont National Forest, Augur Creek, ex Aquilegia – stray?, 30 June 2019 (2 al); AJ 11510, Lake County, Fremont National Forest, N. Warners milepost ~16, ex Holodiscus – stray, 21 September 2019 (1 o); UTAH, AJ 5803, Summit County, Uintas, Bear River, ex Geranium , 21 July 2012 (1 ap); AJ 5816, AJ 5817, AJ 5818, Summit County, Uintas, Mill Creek, ex Geranium , 21 July 2012 (4 ap, 2 al); AJ 7790, AJ 7791, Utah County, Mt. Timpanogos Trail, ex Geranium richardsonii , 20 September 2014 (3 o).

Biology and Distribution. Macrosiphum aetheocornum feeds on native Geranium species, the species recorded by this author have been Geranium richardsonii Fisch &Trautv. and Geranium viscosissimum F. &M. Some collections listed above were recorded as Geranium due to the author’s limited plant taxonomy skills, but some of these were almost certainly species other than G. richardsonii and G. viscosissimum . In plants that are partially sticky–glandular, post–bloom, or that have the common intermediate pink flower color, the author struggles to confidently distinguish between the latter two species of Geranium , so not all species identifications can be relied upon.

Macrosiphum aetheocornum has a full–season life cycle with sexuales in September. This differs from another common aphid that frequently occurs on the same host plants, Nasonovia (Capitosiphon) crenicorna Smith and Knowlton. The latter species has an abbreviated life cycle with sexuales in July and early August. The author has studied an unidentified species of Amphorophora that also has an abbreviated life cycle on especially glandular– sticky populations of G. viscosissimum ; this aphid may be Amphorophora coloutensis Smith & Knowlton , which has a similarly abbreviated life cycle, but available identification keys and references are inadequate for species identification. These aphids with abbreviated life cycles often occupy stands of Geranium in dryer habitats that dry out and enter dormancy during summer. Macrosiphum aetheocornum , on the other hand, with its full–season life cycle occupies plant stands in habitats that support vegetative growth all summer and into autumn. Typical habitats for M. aetheocornum are forested riparian zones and the understory of pine forests, but it can also be found on hot and dry slopes with spring–fed wet soils (such as the slopes above Lake Abert in Lake County, Oregon).

The author has collected M. aetheocornum in Oregon , California , Montana, Idaho, Utah, New Mexico, and Colorado. It almost certainly occurs in neighboring states such as Washington, Nevada, Arizona , and Wyoming.

Comments. The original description of this species uses the presence of setae on the siphunculi as its distinguishing feature, but as noted by Blackman & Eastop (2006), not all specimens have these setae. This variation is within and between populations. Some collections have a mixture of seta–bearing and nonseta–bearing siphunculi, this variation sometimes within a single specimen. Other collections have no setae on siphunculi. The main challenge in recognizing this species, therefore, comes in populations lacking setae on siphunculi. Fortunately, M. aetheocornum has another feature that is unusual: a long, usually setose, R IV+V combined with a short HT II, resulting in an unusually large ratio of these two lengths, 1.21–1.62. Recognizing this species among aphids known to live on Geranium can be done using the key in Blackman & Eastop 2021. The current study revealed slight deviation from characters used in that key including: SIPH x cauda range was expanded to 1.9–2.5, the range of accessory setae on R IV+V was widened substantially to 9–24, and the maximum number of setae on the siphunculi was increased to 9.

Most of the collections this author has seen are easily recognized as M. aetheocornum except some specimens from New Mexico. These specimens, especially in terms of their R IV+V and HT II are concerningly similar to M. euphorbiae . One possible reason for this is that all New Mexico samples were collected in late September when specimens tend to be smaller and have reduced setation (e.g., as few as nine accessory setae on R IV+V).

The reason M. aetheocornum was included in this paper is its similarity to M. ginajo . Morphologically the two species are so similar in most regards that any redescription of M. aetheocornum we might offer would be almost identical to the description of M. ginajo offered above. There are, however, key features in addition to host plant and habitat that distinguish the species. First is the frequent presence of setae on the siphunculi in M. aetheocornum ; no specimen of M. ginajo has such setae. Second, the almost constant presence in M. ginajo of 4 or 5 setae on one or more tarsal segments I; of all M. aetheocornum specimens examined for this work, only one tarsal segment I had 4 setae, none had 5. In fact, some M. aetheocornum specimens have only two setae on some tarsal segments I, apparently lacking the middle “sense peg.” The exceptions within these characters between species further argues for a close relationship between the species and the need for backup characters to support identification of material in the absence of host plant records. One simple feature was recognized during this work: the relative ventral ornamentation of ANT I and II. Figures 7 and 8 illustrate the range of variation of M. ginajo , while Figures 9 and 10 depict M. aetheocornum . Note the much more extensive spinulation of the basal portion of ANT I in M. ginajo . In most specimens, M. ginajo also shows greater ornamentation of ANT II as in Figure 7 , Figure 8 showing unusually reduced ornamentation of this segment. Another general trend of variation between these two species is the shape of secondary rhinaria on ANT III: the small tuberculate rhinaria shown in Figure 9 are common in M. aetheocornum but unusual in M. ginajo , Figure 8 showing a specimen with one small tuberculate rhinarium.

Figures

FIGURE 7–10. Macrosiphum ginajo: 7, ANT I–II and basal part of ANT III of aptera showing typical ornamentation on ANT I–II; 8, ANT I–II and basal part of ANT III of aptera showing a specimen with reduced ornamentation on ANT II and an unusual tuberculate small rhinaria on ANT III; Macrosiphum aetheocornum: 9, ANT I–II and basal part of ANT III of aptera, a specimen with relatively heavy ornamentation on ANT II common tuberculate small rhinaria on ANT III; 10, ANT I–II and basal part of ANT III of aptera, a specimen with relatively typical ornamentation on ANT II. The scale bar equals 100 microns and applies to all four figures.