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Aphidinae : Uroleucon rudbeckiae
 

 

Identification & Distribution

Adult apterae of Uroleucon rudbeckiae (see first picture below) are shiny bright vermillion red with mainly yellowish-brown legs and blackish antennae. Postsiphuncular sclerites and scleroites at the bases of dorsal hairs are pale and inconspicuous. Their femora are pale or dusky, sometimes with a darker patch at the apices. The siphunculi become gradually darker distally, so are much paler at the base than at the apex (cf. Uroleucon ambrosiae, Uroleucon leonardi and Uroleucon nigrotuberculatum, which all have entirely black siphunculi). The siphunculi are rather thick, less than 1.6 times as long as the cauda, with reticulation of small polygonal cells on at least the distal quarter of their length. The cauda is pale yellowish or sometimes dusky. The body length of adult Uroleucon rudbeckiae apterae is 2.4-3.2 mm.

Images above by permission, copyright Claude Pilon, all rights reserved.

Alatae of Uroleucon rudbeckiae (see second picture above) are coloured much the same as the apterae. The antennae are much longer than the body with a paler area near the base; they are sited on large antennal tubercles. The siphunculi are dark over a slightly greater extent than in the apterae, but the base is still pale. The cauda is yellowish red, constricted above the middle, with many lateral hairs on each side, upcurved and acute.

Images above by permission, copyright Claude Pilon, all rights reserved.

Uroleucon rudbeckiae live, usually in large colonies, on the stems of coneflowers (Rudbeckia spp.). Blackman in Aphids on Worlds Plants suggests that records from other Asteraceae genera are likely to be misidentifications. There is no host alternation, with the entire life cycle taking place on Rudbeckia. Sexuales develop in autumn (see picture of male mating with ovipara below), and eggs are laid on the foodplant stems.

Image above by permission, copyright Claude Pilon, all rights reserved.

Uroleucon rudbeckiae is widely distributed in North America from Canada to Mexico.

 

Biology & Ecology

Population dynamics

Lamb & MacKay (2017) used data from a nine-year study of Uroleucon rudbeckiae on Rudbeckia laciniata to investigate the pattern of seasonal abundance of this aphid. Abundance (mean aphids per stem) rose in mid-summer to late summer and then declined, peaking between the end of July and mid-September, earlier in years when the peak was higher. Prevalence (proportion of stems colonised) showed a more uniform and consistent peak than mean intensity (aphids per colonised stem). Most of the colonies were small and short-lived, but a small proportion were long-lived and reached 1000 aphids. Large colonies declined more slowly than moderately-sized colonies. Severe weather, shortening day-length, decline in host quality, density-dependent effects on rate of increase, and emigration failed to explain the population decline. An early rise and later decline in immigration, in conjunction with increasing predation through the summer, were consistent with the decline. {Note: if the 'errors' in these analyses were very non-normal, as seems likely, means may not have been the most appropriate measure.}

 

Other aphids on the same host

Uroleucon rudbeckiae has been recorded on 4 species of Rudbeckia (Rudbeckia amplexicaulis, Rudbeckia flava, Rudbeckia hirta, Rudbeckia laciniata).

Acknowledgements

We are grateful to Claude Pilon for pictures of Uroleucon rudbeckiae (for more of her excellent pictures see).

Identification of specimens photographed by Claude Pilon was confirmed by Eric Maw by microscopic examination and DNA analysis of preserved specimens. For taxonomic details we have used the account of Soliman (1927) and Palmer (1952) together with information from Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

References

  • Lamb, R.J. & MacKay, P.A. (2017). Seasonal dynamics of a population of the aphid Uroleucon rudbeckiae (Hemiptera: Aphididae): implications for population regulation. The Canadian Entomologist 149(3), 300-314. Abstract

  • Palmer, M.A. (1952). Aphids of the Rocky Mountain Region: including primarily Colorado and Utah, but also bordering area composed of southern Wyoming, southeastern Idaho and northern New Mexico. Full text

  • Soliman, L.B. (1927). A comparative study of the structural characteristics of the genus Macrosiphum of the family Aphididae, with special reference to the species found in California. University of California Publications in Entomology 4(6), 90-158.