Biology, images, analysis, design...
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Buckthorn - potato aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:The Aphis nasturtii aptera is rather bright pale green to yellowish-green in life and is not wax-powdered (see aptera below in a mixed species colony of Aphis fabae and Aphis nasturtii). The abdominal dorsum is pale and membranous without dark bands or sclerites. The antenna barely exceeds half the body length. The siphunculi are usually rather pale sclerotic becoming a little darker towards the apex. The legs are dusky or rather pale - the apices of the tibiae are slightly darker as can be seen in the micrograph ventral view below. The body length of buckthorn - potato aphid apterae is 1.1-2.4 mm.
Immature Aphis nasturtii are green (see second picture above). Aphis nasturtii alates (not shown) have some variably developed dorsal bands, but are always more lightly marked than Aphis frangulae alates. The pictures below are micrographs of an aptera in alcohol - dorsal and ventral view.
The buckthorn - potato aphid host alternates between common buckthorn (Rhamnus catharticus) or alder buckthorn (Frangula alnus) as the primary host and many herbaceous plant species as secondary hosts, the most economically important of which is potato (Solanum tuberosum). Sexual forms occur in autumn. Aphis nasturtii is now of almost world-wide distribution.
Biology & Ecology:
We have not found Aphis nasturtii very often because we have not visited many chalk or limestone areas where its primary hosts (buckthorn) are found. Neverthless we did find some mixed species colonies on curled dock near the South Downs in UK. The picture below shows Aphis nasturtii living with Aphis fabae. It is not uncommon to find different species of aphids clustering together when feeding to create a sink effect which improves the flow of nutrients.
Lamb et al. (2011) looked at abundance, persistence, and variability of populations of Aphis nasturtii, Macrosiphum euphorbiae and Myzus persicae in potato plots in Canada. Populations of Aphis nasturtii and Myzus persicae from this crop monoculture were less stable than previously studied natural populations of a native aphid species. In contrast, the population of Macrosiphum euphorbiae, a species native to Canada, had variability in a potato crop similar to that of the previously studied native species. It was proposed that the high population variability of Myzus persicae and Aphis nasturtii may be associated with their status as introduced species. Alyokhinet al. (2007) analyzed similar data in the USA. They found strong evidence of density-dependent regulation of aphid numbers for all three species. Another example of a mixed species population on dock is shown below comprising Aphis nasturtii (yellowish green), Aphis fabae (grey black) and immature Macrosiphum (green small).
Ant attendance does not seem to be reported very often for Aphid nasturtii, but they have been ant-attended when we have found them, as can be seen below.
Damage and control
Aphis nasturtii is an important vectors of potato viruses. It transmits potato viruses Y and A and potato leaf roll virus. There are few confirmed reports of insecticide resistance, but there is anecdotal evidence that it is often not controlled by pirimicarb (a selective acetylcholinesterase-inhibiting insecticide which does not affect predators such as coccinellids) on potatoes in the UK or mainland Europe (Foster, 2006 ).