Megoura crassicauda is the latest unwelcome aphid pest to arrive in Australia, but what impact will it have to faba beans and vetch?
Where is it?
Megoura crassicauda is an aphid species native to north-east Asia, and was considered an exotic pest in Australia prior to its detection on broad bean plants in a suburb of metropolitan Sydney, October 2016.
After this initial detection in Australia, eradication of M. crassicauda was deemed unfeasible based on previous unsuccessful attempts to eradicate exotic aphid species.
It is not known how M. crassicauda first arrived in Australia.
The known distribution of M. crassicauda has expanded to the NSW North West Slopes and Plains, after high infestation levels were found in faba beans. In September 2017, Joop van Leur and Zorica Duric (NSW DPI) detected the infestations near Tamworth and in Breeza. The large distance between these two locations suggests M. crassicauda has established in the region.
It is unclear where else this aphid is present, or how quickly it is likely to spread into new regions.
Hosts and impact
Megoura crassicauda is oligophagous, meaning that it feeds on specific plant species. Its host range is thought to be largely restricted to the Vicia genus of plants, which includes faba beans, broad beans, and vetch.
It has also been reported in field peas in the Korean Peninsula, however this has not yet been observed in Australia and requires further investigation.
There is little known about the potential economic impact of M. crassicauda.
One scientific study demonstrated that while M. crassicauda delayed flower bud formation in narrow-leaf vetch, it did not reduce seed production.
However, observations of its activity in Australia so far indicate that the aphid has a high reproductive capacity and could threaten faba bean production.
For example, the initial M. crassicauda detection in metro Sydney was described as a high population density, covering whole stems and basal shoots of broad bean plants, resulting in blackened, dying shoots and pods. Similarly, in the Tamworth region, very high densities have been reported in several spots within the research trials.
Megoura crassicauda has a very distinctive appearance. Wingless and winged M. crassicauda adults are dark green and spindle-shaped, with long antennae that surpass the length of their bodies.
The head, cauda (‘tail’), siphuncles (‘exhaust pipes’), antennae, and legs are black.
While hard to see with the naked-eye, M. crassicauda has vibrant, red eyes.
They are relatively large aphids, approximately 2.5 – 3 mm in length.
Megoura crassicauda can form mixed colonies with pea aphid (Acrythosiphons pisum) and cowpea aphid (Aphis craccivora), two species which are widespread in Australia and infest faba beans and vetch.
In Australia, observations of M. crassicauda in faba beans suggest that it has similar colonisation habits to cowpea aphid, which form dense colonies on individual plants. However, as cowpea aphid is almost entirely black, it is can be distinguished from M. crassicauda with the naked eyed.
M. crassicauda is unlikely to be mistaken for pea aphid, which is light green with legs, antenna and siphuncles that are pale green-yellow in colour.
Some confusion exists around the common name of this pest.
Overseas, M. crassicauda is sometimes referred to as the vetch aphid, however this name more commonly refers to the closely related Megoura viciae, which is not present in Australia.
Megoura crassicauda is also sometimes referred to as bean aphid, however this should not be confused with the black bean aphid (Aphis fabae), also not present in Australia.
For now, it is appropriate to use the scientific name to avoid adding to the confusion.
Biology and behaviour
Available information on the lifecycle and behaviour of M. crassicauda is limited.
They are known to reproduce asexually (female aphids giving birth to live nymphs without mating), and sexually (females lay eggs after mating).
While the conditions necessary for the two modes of reproduction require further investigation, research shows M. crassicauda aphids produced from either mode have a poor survival rate in extremely cold environments.
Prospects for control
Chemical controls which have been tested to date in Australia include imidacloprid, petroleum oil, and pirimicarb.
The infestations at TAI have been successfully controlled with pirimicarb (500 g/kg) at a rate of 0.5 g/L.
Permits are being applied for pirimicarb, chlorpyrifos, dimethoate, and lambda-cyhalothrin.
The role of natural enemies in controlling M. crassicauda remains unclear. While likely that beneficial insects will be important in the ongoing management of this pest (as they are with all crop aphids), the presence of parasitic wasps, ladybird beetles, and hoverflies had no noticeable effect in controlling the initial infestation on broad beans in Sydney. Similarly, the NSW DPI researchers have observed only a few ladybird beetles feeding on M. crassicauda despite very high infestations. There is some evidence that the closely related vetch aphid (M. viciae) is toxic or unsuitable to certain species of ladybird beetle predators.
Where to next?
Undoubtedly, we will learn more about M. crassicauda in the Australian context with time, including the role of natural enemies, its potential as a virus vector, and how it will behave and spread in our climate.
Growers and agronomists are encouraged to report suspected cases in NSW to Zorica Duric (firstname.lastname@example.org) or Rachel Taylor-Hukins (email@example.com).
The NSW DPI will also be checking commercial faba bean crops and roadside vetches for M. crassicauda presence over the coming weeks.
Growers and agronomists can also seek identification assistance from the PestFacts team here at cesar through high quality photos and samples.
Zorica Duric – NSW Department of Primary Industries (North West Slopes & Plains, NSW)
Joop van Leur – NSW Department of Primary Industries (North West Slopes & Plains, NSW)
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Hales DF, Gillespie PS, Wade S and Dominiak BC. 2017. First detection of Megoura crassicauda Mordvilko (Hemiptera: Aphididae) in Australia and a review of its biology. General and Applied Entomology 45: 77 – 81.
Kasai A. 2016. Vetch aphid, Megoura crassicauda (Hemiptera: Aphididae), parasitism does not reduce the bean production of narrow-leaved vetch, Vicia sativa subsp. nigra (Fabaceae). Ecological Research 31: 189–194.
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