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Toadflax flower aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Adult apterae of Myzus linariae (first picture below from USA, second & third from UK) are yellowish-green to yellow, with a pale dorsum that is uniformly sclerotized, and wrinkled in parts, with tranverse rows of spinules. Dorsal hairs are very short. The head has large antennal tubercles, with a wide, low median frontal tubercle. The antennae are 0.6-0.75 times as long as the body, with the apices of antennal segments V & VI darker. The terminal process is about 2.35-2.85 times the base of antennal segment VI (cf. Myzus antirrhini, which has the terminal process 3.74-4.95 times the base of segment VI). The terminal process is shorter (0.65-0.85 times) than antennal segment III (cf. Myzus persicae, which usually has the terminal process longer (0.90-1.49 times) than segment III). Antennal hairs are short and blunt, about 0.25-0.33 times the basal diameter of antennal segment III. There are no secondary rhinaria. The rostrum reaches to, or slightly beyond, the middle coxae, with the apical rostral segment (RIV+V) 0.63-0.88 times the second hind tarsal segment (HTII). The siphunculi are dusky with a pale base and dark apex, slightly swollen in the apical half, and 1.5-1.8 times the caudal length. The cauda is elongated, tongue-shaped with a dusky, usually wax-covered tip. The body length of adult Myzus linariae apterae is 1.6-2.3 mm.
First picture above, copyright Andrew Jensen, under a creative commons licence.
Alatae of Myzus linariae (see pictures below) are green with large marginal sclerites on segments II-IV, plus rather narrow antesiphuncular and large postsiphuncular sclerites. They also have a wide tranverse bar on VII and a small one on segment VIII, with a central trapezoid pattern on tergites III-VI. The antennae are dark except for the very base of segment III, and on that segment bear 10-16 rather flat secondary rhinaria arranged along the whole length of segment III. The siphunculi are distinctly swollen, dusky on the basal half, then pale on the distal half, but with dark tips.
Myzus linariae feeds on the upper parts and inflorescences of toadflax (Linaria spp). Like Myzus antirrhini (but unlike Myzus persicae) they live in dense colonies (see picture below). The species is monoecious holocyclic in Europe, with oviparae and apterous males in September-October. The species is native to southern Europe (Czech and Slovak Republics, Serbia, Hungary, Italy) and west Asia (Turkey). Andrew Jensen in AphidTrek has recently reported its occurrence on Linaria dalmatica in western USA, and we now report it here from southern England.
Biology & Ecology
Discovery in Britain
Until 2022 Myzus linariae was unrecorded in Britain. In May 2022, in Rye Harbour Village, East Sussex, England we came across some flowering plants of purple toadflax (Linaria purpurea) that were heavily infested with green aphids. In appearance they resembled Myzus persicae or Myzus antirrhini. However, Myzus persicae tends to feed dispersed on the lower, older leaves, whilst these were dense, crowded populations on the young leaves and inflorescences. Given the dusky swollen siphunculi, we first thought that these were Myzus antirrhini, a species present in England, but which we had yet to find. The other possibility was Myzus persicae, albeit neither of these polyphagous Myzus species have ever been previously recorded on Linaria purpurea.
Subsequent examination of several apterae (n=4-6) revealed certain interesting characteristics. The terminal process was only 2.6-3.0 times the base of antennal segment VI, much shorter than for either Myzus antirrhini (3.75-4.95 times) or Myzus persicae (3.14-4.10 times). Moreover, the terminal process was shorter than (0.78-0.93 times) antennal segment III, whereas both Myzus antirrhini and Myzus persicae have a terminal process usually longer than (0.90-1.49 times) antennal segment III. The apical rostral segment was also shorter (0.83 times) than the second hind tarsal segment, whilst both Myzus antirrhini and Myzus persicae have the apical rostral segment 0.9-1.2 times the hind tarsal segment. A short terminal process and short apical rostral segment are key characteristics of the monophagous Myzus linariae, and rule out both the polyphagous species in the Myzus persicae species group.
Purple toadflax (Linaria purpurea) is a small but conspicuous herbaceous flower, introduced to the UK many years ago, and now common not only in flower beds, but also on walls and in waste ground. We have often looked it over for aphids and never found any, and infestations by this species are very conspicuous. The appearance of this 'warmth-loving' aphid in two separate locations strongly suggests a recent introduction to southern England, either through the plant trade, or by natural alate dispersal via convective air currents (e.g. during thunderstorms) from continental Europe as the climate warms.
Other aphids on the same host
Myzus linariae has been recorded on 4 toadflax species (Linaria genistifolia, Linaria genistifolia ssp. dalmatica, Linaria heterophylla, Linaria propinqua), to which we can add Linaria dalmatica from Western America and Linaria purpurea from UK. The only aphid species previously reported on Linaria purpurea was Brachycaudus linariae.
Blackman & Eastop list 2 species of aphid as feeding on Linaria genistifolia worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 2 as occurring in Britain (Show British list).