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Identification & Distribution

Dysaphis crithmi live concealed in the sheathing leaf bases of rock samphire (Crithmum maritimum, see first picture below) growing in sheltered locations. Adult Dysaphis crithmi apterae (see second picture below) are grey to greenish grey, with a reddish area around their siphunculi. The colour is largely obscured by a thick layer of wax-powder. The antennal terminal process is 2.0-3.0 times the length of the base of antennal segment VI. The longest hairs on antennal segment III are 0.6-1.1 times longer than the basal diameter of that segment. The head and abdominal tergites VIII may have very small spinal tubercles. The rather short black siphunculi are only 1.25-2.0 times longer than the cauda. Their cauda is helmet-shaped, not longer than its basal width in dorsal view, with 4-5 hairs. The body length of adult Dysaphis crithmi apterae is 1.7-2.2 mm. Early instars (see third picture below) are pale ochreous, turning to greenish grey with a reddish area around the siphuncular bases as they mature.

The micrographs below show dorsal and ventral views of a Dysaphis crithmi aptera in isopropyl alcohol.

Alate Dysaphis crithmi (not pictured live) are pale ochreous greyish on the non-sclerotised parts, with slight wax powdering on the ventral surface. They have large dark marginal marginal sclerites and a black mid-dorsal patch on the abdomen (see second clarified mount below).

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

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

Dysaphis crithmi colonies live in the sheathing leaf bases of samphire (Crithmum maritimum) growing in sheltered situations, such as rock clefts and crevices in sea walls. Their colonies are usually ant-attended. Dysaphis crithmi is thought to be completely anholocyclic - sexual forms are unknown. It is found in western and southern Europe, including the Iberian peninsula and the Mediterranean islands of Corsica, Malta, and Cyprus.

 

Biology & Ecology

Habitat

The host plant, rock samphire (Crithmum maritimum) is found on the southern and western coasts of Britain and Ireland, and on the Mediterranean and western coasts of Europe including the Canary Islands, North Africa and the Black Sea. The rock samphire aphid has, so far, only been found on western and southern European coasts and the coasts of Mediterranean islands. In Britain Stroyan (1963) reported finding Dysaphis crithmi common on Crithmum over a wide stretch of the south-western coasts of Britain, from Pembrokeshire to the Isle of Wight. We have found it on plants growing between rocks emplaced to protect the underclif base at Barton-on-Sea, Hampshire (see picture below), but so far not further east (East & West Sussex) despite the presence of its food plant.

Dysaphis crithmi live out of sight concealed in the leaf sheaths of Crithmum. Stroyan (1963) noted that he had never found it on Crithmum growing in fully exposed situations, or where the roots did not emerge from cracks or crevices of some kind. He hypothesised that this was because aphids needed to penetrated such sites for shelter in the winter, there being no evidence that they retained the sexual stages (males and oviparae), and so could not overwinter as eggs. The pictures below shows Dysaphis crithmi colonies living in the leaf sheaths of the plants above.

Life cycle

Very little is known about this species other than that reported by Stroyan (1963). It, like its very close relative Dysaphis tulipae, is entirely anholocyclic. Neither sexual stages nor fundatrices are known, despite samples having been taken in late autumn and early spring.

The picture above shows two adult viviparous apterae together with a ?second instar nymph.

The picture above shows a first instar nymph. Very young nymphs are pale ochreous with a slight pinkish hue over the anterior parts.

Third instar nymphs (see picture above) are grey-green with marked orange-red coloration around and between the siphunculi.

The last picture above shows an adult aptera along with a nymph. We sampled at Barton-on-sea in September, so it is not surprising that we found no alates in the colonies. Alates have been observed in colonies in Britain between April and July (Stroyan, 1963).

Ant attendance

The aphids we found were usually attended by ants, which provided the best way to identify infested plants. However attendance was not close, and the ants always departed when the colonies in the leaf sheaths were exposed.

The ants that we found (see picture above) have yet to be identified. Stroyan (1963) found Lasius niger attending large colonies in the Isle of Wight in April, but reported that there was no ant attendance for smaller colonies in Devon and Cornwall in September and October.

 

Other aphids on the same host

Blackman & Eastop list 5 species of aphid as feeding on Samphire (Crithmum maritimum) worldwide, and provide formal identification keys.

Of those aphid species, Baker (2015) lists 5 as occurring in Britain: Aphis fabae, Cavariella aegopodii, Dysaphis crithmi, Hyadaphis foeniculi, and Macrosiphum ?centranthi.

We have found two species of aphids, other than Dysaphis crithmi, on Crithmum maritimum growing on the Dorset coast. The first was a Cavariella species, most likely Cavariella aegopodii since for the alate the ratio of the antennal terminal process to the base of antennal segment VI (PT/base) was slightly less than 1.5 (see pictures below).

The other species was most likely Aphis fabae.

 

Damage and control

It is unlikely that Dysaphis crithmi would be considered a pest, let alone be controlled, given that only a small proportion of rock samphire plants (those in sheltered sites) are likely to be infested, and the plant is little-used at present. Prior to the early 20th century however, large quantities of rock samphire (also known as sea fennel or sea asparagus) were picked for food.

In Victorian times rock samphire was apparently harvested from the south coast of Britain, and transported to London in casks of salt water to be sold in street markets (Grigson, 1948). The fresh young growth consisting of fleshy leaves and stems was either eaten raw as a salad vegetable, cooked with fish or pickled and served with for example quails eggs. Although no longer available commercially, rock samphire may be coming back into fashion amongst enthusiasts and restauranteurs - see Galloway Wild Foods and Produce Business UK.

Acknowledgements

We have made provisional 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

  • Grigson, G. (1958). The Englishman's Flora. The Readers Union, Phoenix House. London.

  • Stroyan, H.L.G. (1963). The British species of Dysaphis Börner. (Sapaphis auct nec Mats.). Part 2. HMSO, London.