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Purple loosestrife aphidOn this page: Identification & Distribution Biology & Ecology: Colour Natural enemies Other aphids on the same host Biological Control of Lythrum Damage & Control
Identification & Distribution
Adult apterae of Myzus lythri (see first picture below) are light green to yellow. On their secondary hosts the anterior part of the body is frequently brownish, and the posterior parts reddish. The head and first two antennal segments are granular, and the cuticle is wrinkled. The antennae are 0.5-0.6 times the body length, and the antennal terminal process is 2.4-3.0 times the length of the base of the sixth antennal segment. The antennal tubercles are low and the median frontal tubercle is broad. The pale siphunculi are cylindrical, scaly, and 2.3-2.8 times the length of the pale tongue-shaped cauda. The body length of the adult Myzus lythri aptera is 1.5-2.4 mm.
The alate of Myzus lythri (see second picture above) has a light green to yellow abdomen, with a dark patch on tergites II-VI, and marginal and postsiphuncular sclerites. The siphunculi and cauda are brown.
In central Europe Myzus lythri host alternates from mahleb cherry (Prunus mahaleb) to purple loosestrifes (Lythraceae) and willow herbs (Onagraceae). In some other parts of the world (including Russia and possibly Britain) it reproduces parthenogenetically on Lythrum species all year round. The aphid is found throughout Europe and much of Asia, and has been introduced to central Africa (Burundi) and North America.
Biology & Ecology
The dorsum of the adult aphid is yellowish or orange-yellow, mottled with light green.
The picture above shows Myzus lythri on one of its (secondary) hosts, willowherb (Epilobium). The aphid's colour matches well with the greenish parts of the stem. The adult aptera also appears to mimic the buds in both size and shape as well as color, as can be seen in the picture below.
Their cryptic coloration aside, Myzus lythri adults are cryptophilic (= concealment-loving). They hide by putting the head and thorax into the leaf axil or under protruding buds (see picture below).
We have also found Myzus lythri on its namesake host, purple loosestrife (Lythrum salicariae, see picture below).
On the purple loosestrife there were both green forms and red forms of the immature aphids, the latter matching perfectly with the colour of the loosestrife stems.
Myzus lythri was one of the species examined by Francis (2005) who was looking at whether (E)-β-farnesene is the only volatile terpenoid in aphids. (E)-β-farnesene is a well-known aphid alarm pheromone released when aphids are attacked by predators, which had been found in all previous tested aphid species. EBF proved to be the main volatile substance in Myzus lythri (83.3% of the volatile substances released), but it was associated with two other molecules, an unidentified sesquiterpene hydrocarbon (3.9%) and an unknown molecule (12.8%). EBF was, however, not released by all the aphid species tested.
Other aphids on same host:
Myzus lythri has been recorded from 4 Prunus species (Prunus cerasifera, Prunus domestica, Prunus emarginata, Prunus mahaleb) - but not in Britain.
Potential for Biological Control of Lythrum in USA
The case for biological control of purple loosestrife in the USA is put forcefully by Blossey et al. (2001). The invasion of purple loosestrife into North American freshwater wetlands alters decomposition rates and nutrient cycling, leads to reductions in wetland plant diversity, reduces pollination and seed output of the native Lythrum alatum, and reduces habitat suitability for specialized wetland bird species.
Conventional methods, either physical, mechanical or chemical, have continuously failed to curb the spread of purple loosestrife or to provide satisfactory control. Although a number of generalist insect and bird species utilize purple loosestrife, wetland habitat specialists are excluded by encroachment of Lythrum salicaria. Blossey et al. conclude that negative ecosystem impacts of purple loosestrife in North America justify control of the species and that the detrimental effects of purple loosestrife on wetland systems and biota and the potential benefits of control outweigh potential risks associated with the introduction of biocontrol agents. Monitoring programs are in place to evaluate the impact of the beetles that have been released (two leaf feeding Galerucella species and a root feeding weevil, Hylobius transversovittatus) on purple loosestrife and other wetland biota. The picture below shows larvae of one of the leaf feeding beetles, Galerucella calmariensis.
Agriculture and Agri-Food Canada Archive, Agriculture and Agri-Food Canada, Bugwood.org CC BY 3.0, via Wikimedia Commons.
The European purple loosestrife aphid (Myzus lythri) was not introduced as part of the biological control programme, but was introduced accidentally to America in the 1930s. Voegtlin (1995) looked at whether the purple loosestrife aphid could supplement the biocontrol of purple loosestrife. The complex life cycle and low availability of primary host plants were hypothesized as limiting early-season development of aphid populations on purple loosestrife. Experiments were undertaken to determine if large populations of this aphid could influence the growth and development of purple loosestrife. Two-year plants each inoculated with five aphids showed significantly lower root and shoot weight after a 7 week period as compared with matched controls. Over half of 20 seedlings (3 months old) inoculated with two or five Myzus lythri were dead or clearly dying 11 weeks after inoculation. Mass rearing for early-spring release and planting primary hosts are possible methods to augment the potential of this aphid to function as a biological control agent for purple loosestrife.
Matos & Obrycki (2006) looked at how the presence of Myzus lythri may affect the biological control of purple loosestrife by Galerucella calmariensis. Various aphid predators including Harmonia axyridis and Chrysopa carnea are attracted to populations of Myzus lythri, but will also feed on Galerucella larvae. Based on their study, they predicted that an increase in Myzus lythri populations on purple loosestrife plants may initially reduce predation of Galerucella by providing a preferred alternative host. However, over a longer time period, these predatory species may numerically respond to Myzus lythri populations, resulting in an increase in the numbers of predators present on purple loosestrife plants, and increased predation on Galerucella.
Halbert & Voegtlin (2005) found that suction trap collections of Myzus lythri reflected the distribution of its foodplant, purple loosestrife, and could be used to successfully predict undocumented weed populations.
Damage and control
Purple loosestrife is not generally regarded as a pest in Europe, and is often grown as a decorative plant in gardens. Myzus lythri is sometimes regarded as a pest in this situation, but is seldom abundant enough to cause serious damage.