Biology, images, analysis, design...
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Identification & Distribution:Adult apterae of Staticobium staticis are dirty green or dirty red. The antennal segments I and II and the tips of the antennae, knees, tips of tibiae and tarsi are dark. The antennae are 0.6-0.9 times the body length. Short blunt body hairs are placed on small, dark scleroites. The body length of Staticobium staticis is 2.4-2.7 mm.
Staticobium staticis alates are green or red with rather distinct marginal sclerites and well developed postsiphuncular sclerites. The siphunculi and cauda are rather thin. The oviparae are dark brown with a reddish anterior. The apterous males of Staticobium staticis are green or olive with brown spots around the siphuncular bases.
The sea lavender aphid does not host alternate. Staticobium staticis feeds on Statice limonium (sea lavender) on the leaf blade and on the upper parts of the stem under the flowers.
Biology & Ecology:
We have so far only found the sea lavender aphid at one site in UK - at Keyhaven Marshes in Hampshire. This is partly because there are not that many areas on the South Coast of Britain where its host, that iconic salt marsh flower, the sea lavender (Limonium vulgare) can be found. This plant is a salt marsh specialist par excellence and typically form dense monospecific stands on marsh landscapes. It also grows on sea walls where it is rather easier to access and photograph (see below).
Foster (1984) recorded very high densities of more than 50000 Staticobium staticis per square metre on a salt marsh in Norfolk. The dense populations were in the middle of the marsh with low numbers in the lower and upper zones of the marsh. We have only ever found small isolated colonies (see below) - possibly because the delights of sloshing about in the middle of a salt marsh tend to keep us fairly close to the shore!
Four species of sea lavender occurred in the salt marsh in Norfolk: Limonium vulgare, Limonium humile, Limonium bellidifolium and Limonium binervosum. Foster (1984) found the sea lavender aphid on all four species of sea lavender, but their susceptibility varied markedly. Heavy infestations occurred on both Limonium vulgare and Limonium humile suggesting they were both equally liable to attack. Limonium binervosum was occasionally attacked in peak years but aphid density was very low. Only one aphid was ever seen feeding on Limonium bellidifolium. We have searched for it unsuccessfully on Limonium hyblaeum at Rye Harbour in Sussex.
Foster's study was mainly dedicated to 'disproving' a hypothesis put forward by Owen & Wiegert (1976) who suggested that aphids could actually benefit their plant hosts. They proposed that honeydew excreted by the aphids acted as a carbohydrate source for soil-living, nitrogen-fixing bacteria, thus increasing the rate of nitrogen fixation which would subsequently benefit vascular plants. Foster, however, demonstrated experimentally that the sea lavender aphid instead dramatically reduces the fitness of its host plant (as measured by its seed production) under natural conditions. Untreated heavily infested plants produced no seed at all, whilst plants in plots that were treated with insecticide to kill the aphids set seed normally.
One example cannot of course 'disprove' a hypothesis, and Adam (1993) pointed that the large dense single species populations of plants on saltmarshes are not typical of natural systems. In this respect saltmarshes are more similar to agricultural systems where we are fully aware that aphids may greatly reduce plant fitness. Another weakness of Foster's study is that the amount of honeydew reaching the salt marsh floor was not actually measured, and much of it may have remained on the plant. Nevertheless Owen & Wiegert's hypothesis has not gained many supporters in recent years.
Given the 'challenging' conditions on a saltmarsh, we would expect Staticobium staticis to show some clear morphological and physiological adaptations to its environment. One such modification is that the spiracles are covered by tubercle-like opercula. These apparently enable the aphids to survive several hours submergence in aerated seawater (Foster & Traherne, 1976) , albeit nowhere near as long as the root feeding aphid Pemphigus trehernei which can survive up to 20 days in aerated seawater.
Starý (1976) records Aphidius absinthii and Praon dorsale as parasitoids of Staticobium. In Slovenia Kos et al. (2012) found the parasitoids Ephedrus plagiatorand Praon necans parasitizing Staticobium limonii. They also described a new aphid parasitoid species Aphidius staticobii parasitizing Staticobium limonii on Limonium angustifolium. Apart from these observations very little has been published about predators and parasitoids of the sea lavender aphid. We found none attacking the Keyhaven populations.