Rhopalosiphoninus calthae

Identification & Distribution:

Apterae of Rhopalosiphoninus calthae are shining brownish black. The antennae are dark except for the basal part of segment III, and the legs are yellowish. The dorsum has an almost complete black sclerotic shield. The black siphunculi have a narrow, almost cylindrical stem, which widens abruptly to the swollen half which is about 3 times thicker than the narrower part of the stem. The siphunculi are 3.5-4.6 times the length of the cauda.

Alatae have a large black dorsal abdominal patch and strongly swollen siphunculi like the apterae. Immatures have wax deposits, especially over their anterior part.

The clarified slide mounts below are of adult viviparous female Rhopalosiphoninus calthae : wingless, and winged.

Micrographs of clarified mounts by permission of Roger Blackman, copyright AWP all rights reserved.

The marsh marigold aphid does not host alternate. It feeds on the underside of leaves of marsh marigold (Caltha palustris), especially those growing in the shade. Sexual forms occur in autumn. The male is small, black and apterous, and the ovipara lacks the sclerotic tergum and has slightly swollen hind tibiae. Rhopalosiphoninus calthae is found over most of Europe.

Biology & Ecology:

Large Rhopalosiphoninus calthae colonies may develop, with aphids covering most of the leaves.

Many of the immatures in this colony were alatoid - in other words they were destined to develop into alates, and then migrate to other host plants.

The function of the enormous swelling of the siphunculi, a feature this species shares with the polyphagous Rhopalosiphoninus latysiphon and a few other species, is still unknown (Heie, 2009).

We have recorded syrphid larvae predating Rhopalosiphoninus calthae on marsh marigold (see picture above). Ali et al. (2009) found that the syrphid Ischidon scutellaris was an especially efficient predator of aphids on water plants.

Other aphids on same host:

Rhopalosiphoninus calthae has been recorded from 1 Caltha species (Caltha palustris), but also from Aconitum leucostomum.

• Blackman & Eastop list 9 species of aphid as feeding on marsh marigold (Caltha palustris) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 8 as occurring in Britain (Show British list).

Acknowledgements Our particular thanks to Roger Blackman for images of his clarified slide mounts. Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors 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 Ali, A. et al. (2009). On the predation of aphids by Ischiodon scutellaris (Diptera: Syrphidae) under natural environment. Bionotes 11(3), 95-96.Full text Heie, O.E. (2009). Aphid mysteries not yet solved/Hemiptera:Aphidomorpha. Monograph: Aphids and other hemipterous insects 15, 31-48.  Full text