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22 | February/March - 2017 | 23
R&D | THE FRONT LINE |
In this edition of The Front Line, AUSVEG Biosecurity Coordinator Callum Fletcher profiles the Black bean
aphid (BBA, Aphis fabae). BBA, also commonly known as Black fly, poses a potential threat to the potato
industry and other crop industries should it arrive and establish itself in Australia.
BLACK BEAN APHID:
A BIOSECUR I TY THREAT TO AUSTRAL IA
steadily multiplying and clustered aphids and it subsequently dies.
The broad host range is matched by BBA’s ability to transmit a
high number of plant viruses. It is known to carry approximately
42 viruses, making its potential arrival in Australia a problem for
the majority of plant growing industries. The optimal weather
conditions and broad distribution of host plants mean that the
potential for establishment and spread of BBA in Australia is
very high.
THREAT TO GROWERS
BBA ranges from 1.5-3mm long, is completely black (or very
dark green) in appearance and is usually found clustered together
in large numbers. Along with some feeding damage and secretion
of honeydew that causes Sooty mold, the main harm that this
aphid would bring to potato growers is that it transmits viruses,
including Potato virus Y (PVY), Potato leaf roll virus (PLRV) and
Potato virus A (PVA).
The aphid overwinters on European spindle plants (commonly
found in Australia) and winged aphids spread to host plants in the
warmer months. When colonies of aphids get too large for the
plant host and it begins to die, winged aphids are produced that
seek out new plant hosts.
It is these winged aphids, which fly into the crop during the
Australia is unique in that it is one of only a small number of
countries, along with New Zealand, where Black bean aphid (BBA,
Aphis fabae) is not currently present. The pest is found in higher
numbers in the temperate zones of the world and throughout
North and South America, Africa, Europe and Asia.
The closest countries to Australia where it is found are Malaysia
and the Philippines, although proximity is not the only determiner
of biosecurity risk. Pests have arrived in Australia after sailing
halfway around the world in shipping containers.
BROAD HOST RANGE
As its name suggests, the aphid is a major pest on bean crops
where it colonises in large numbers (adults can produce over
five young per day at the optimal temperature of mid-20 degrees
Celsius) and it causes severe feeding damage. However, the aphid
is not limited to these hosts.
BBA is highly polyphagous, meaning that it has a broad range
of host plants that it can feed on. There are 81 known host species,
including many common weeds and crops such as tomatoes,
spinach, carrot, maize and potatoes.
The aphid is attracted to the younger plants or the younger
shoots on a plant, compounding the effects of feeding damage
as the small plant is unable to cope with the large number of
spring and autumn months and find new hosts throughout the
summer, which are the major cause of concern for potato growers.
Winged BBA transmit PVY, PLRV and PVA as they fly from plant to
plant, probing the leaves, picking up and transmitting viruses as
they attempt to find a preferred host plant to begin colonising.
APHID VIRUS TRANSMISSION
The rate at which different aphid species are able to effectively
transmit viruses, which can be known as relative efficiency factors
(REF), is important to measure.
In terms of PVY transmission, Green peach aphid (GPA, Myzus
persicae) is the most efficient species of aphid vector. Experiments
have been conducted that measure how effectively various isolates
of PYV are transmitted by the different aphid species that feed on
potato crops. On a range of 0-1, GPA has a REF of 1, while BBA has
a REF of 0.07. These results have been published in Determination
of aphid transmission efficiencies for N, NTN and Wilga strains of
Potato virus Y. Other reports have given BBA a score of 0.1 for
PVY and 0.3 for PLRV.
Winged BBL can transmit PLRV into potato crops. This virus
is persistent, meaning that once it has been introduced to the
aphid by feeding on an infected plant, it stays in the aphid and
is able to be transmitted for the rest of its life.
Winged BBL can also transmit PVY, which is a non-persistent
virus. This means that when the aphid feeds or probes the leaf
to see if it is an appropriate host plant, the virus is introduced
into its mouthparts. When it probes another plant, the virus
can be transmitted.
As potato plants are not the most preferred host, winged
BBA tend to feed on them just for sustenance. They will tend to
move to multiple plants, spreading PVY, as they seek their
preferred host to colonise.
Overseas experiences of trapping in potato crops tend to find
large numbers of winged BBA, along with other potato aphids;
as a consequence it is not an insect that the Australian potato
industry would want to arrive on our shores.
ANTS AND BLACK BEAN APHID:
A UNIQUE RELATIONSHIP
Black bean aphid (BBA, Aphis fabae) is a species of aphid that
secretes honeydew and as a consequence, it has developed
a mutualistic relationship with many common species of ants
that farm them.
Ants collect the sugar-rich honeydew which serves as a
food source, and in return protect the aphids from predators.
It has been shown that a higher sugar content correlates with
a greater level of ant attendance.
Ants also milk the aphids, pushing on their abdomen to
encourage honeydew secretion. This symbiotic relationship
even extends to seeking out and destroying the eggs or
predators, like lady bugs.
Other protective behaviour that has been observed includes
moving aphid eggs to spend the winter in their own nests and
removing aphids infected with a toxic fungus away from the
others to stop the spread of infection.
When the number of aphids on a plant become too great,
ants move young aphids to new plants to start another colony
farm, rather than have winged aphids develop. This desire to
keep the colony in place has even resulted in observations of
the ants pulling the wings off aphids so they do not leave.
Any unusual plant pest should be reported immediately to the relevant state or
territory agriculture agency through the Exotic Plant Pest Hotline: 1800 084 881.
For further information, contact AUSVEG National Manager – Science and
Extension Dr Jessica Lye or AUSVEG Biosecurity Coordinator Callum Fletcher on
03 9882 0277 or or
The Vegetable and Potato Biosecurity Program is funded by the Plant Health Levy.
This communication has been funded by Horticulture Innovation Australia Limited
using the Fresh Potato Levy and funds from the Australian Government.
Project Number: PT15007
INFO
Ants defending Black bean aphids from a lady bug. Ants with Black bean aphids.