Aphids

Turnip aphid on canola

A wide range of aphid species can affect field crops. Most are small (only a couple of millimetres long) with oval-shaped green, brown or black bodies. Often occurring in colonies, aphids suck on plant sap, causing loss of vigour, and in some cases yellowing, stunting or distortion of plant parts. Secreted honeydew (unused sap) can promote the development of sooty mould. In crops such as cotton, the honeydew affects fibre quality.

Their feeding rarely causes major damage in most crops, and control measures are usually not warranted, as a range of parasites and predators keep population numbers down. Exceptions may be where:

  • the crop is under moisture stress
  • heavy populations are observed
  • virus outbreaks are likely to be a problem.

Sampling and threshold information for aphids in cotton is available in the Cotton Pest Management Guide.

Aphid pests of field crops

Aphid species found in cereal crops include:

  • Diuraphis noxia—Russian wheat aphid
  • Metopolophium dirhodum—rose-grain aphid
  • Rhopalosiphum maidis—corn aphid
  • Rhopalosiphum padi—oat aphid, wheat aphid
  • Rhopalosiphum rufiabdominalis—rice root aphid.

Aphid species found in broadleaf field crops include:

  • Acyrthosiphon kondoi—bluegreen aphid
  • Acyrthosiphon pisum—pea aphid
  • Aphis craccivora—cowpea aphid
  • Aphis glycine—soybean aphid
  • Aphis gossypii—cotton aphid
  • Brevicoryne brassicae—cabbage aphid
  • Lipaphis erysimi—turnip aphid
  • Megoura crassicauda—faba bean aphid
  • Myzus persicae—green peach aphid
  • Therioaphis trifolii—spotted alfalfa aphid.

Aphids as virus vectors

When aphids transmit viruses, the impact on crop growth and yield can be significant. The earlier the transmission of virus, the greater the potential impact.

Aphid species

Plant hosts

Vector for
Blue green aphid Canola, pulses, lucerne & other pasture legumes
  •  Cucumber mosaic virus (CMV)
Cabbage aphid Canola and other brassica crops and weeds
Corn aphid Sorghum, winter cereals, pasture grasses
  • Barley yellow dwarf virus (BYDV)
Cotton aphid Cotton and weeds
  • Cotton bunchy top (CBT)
Cowpea aphid Pulses, pasture legumes, potatoes
  • Cucumber mosaic virus (CMV) in lupins, lentils, faba beans, chickpeas
  • Bean yellow mosaic virus (BYMV) in faba beans, lupins
  • Alfalfa Mosaic virus (AMV) in lentils, lupins, chickpeas
Faba bean aphid Faba bean and vetches, lucerne
  • Bean leaf roll mosaic virus (BLRV)
  • Pea seed-borne mosaic virus (PSbMV)
Green peach aphid Canola, wild radish and wild turnip, lupins, capeweed plus others
  • Beet western yellows virus (BWYV)
Oat aphid Winter cereals, pasture grasses
  • Barley yellow dwarf virus (BYDV)
Pea aphid

 

 Faba beans, field peas, lucerne
  • Cucumber mosaic virus (CMV)
  • Pea seed-borne mosaic virus (PSbMV)
  • Bean yellow mosaic virus (BYMV)
Rose grain aphid Winter cereals, grasses
  • Barley yellow dwarf virus (BYDV)
Russian wheat aphid Barley and wheat highly susceptible. Oats tolerant. Other winter cereal crops intermediate

Not known to build up in sorghum.

 Can transmit BYDV, but is not as effective a vector as the other cereal infesting aphid species.
Soybean aphid Soybeans Not known to transmit virus within Australia. In China it transmits soybean mosaic virus.
Turnip aphid Canola and other brassica crops and weeds

Aphid parasitism

Parasitised aphids (mummies) by the wasp Aphidius colemani

Aphid parasitoids are small wasps that lay their eggs inside the body of aphids. The larva develops, slowly eating the aphid and killing it before the wasp completes development and emerges from the dead aphid. In the process of developing, the wasp larva spins a cocoon inside the aphid. These swollen, brown ‘mummies’ are evidence of parasitoid activity in an aphid colony. The emerging wasp cuts an exit hole in the remains of its host.

Parasitoids detect aphids from odours produced by both the aphid and the infested plant. Parasitoids are able to detect small numbers of aphids, and therefore have the potential to suppress these small populations, preventing them establishing and increasing to outbreak proportions.

Common and widespread species of aphid parasitoids and their hosts include:

  • Lysiphlebus testaceipes: corn aphid, oat aphid and cowpea aphid
  • Aphidius colemani: green peach aphid, turnip aphid, corn aphid and oat aphid
  • Aphidius ervi: rose grain aphid, blue green aphid and pea aphid
  • Diaeretiella rapae: cabbage aphid

Parasitoids don’t have it all their own way. Aphids can fight back—wasps may be injured by large aphids, or entangled in the cornical wax that the aphids secrete in response to parasitoid activity in the colony.

Surveillance for resistance in cotton aphids

A CRDC-supported surveillance program of cotton aphids by NSW DPI has found populations from NSW, and southern Qld in the in 2022/23 season were susceptible to sulfoxaflor and thiamethoxam with very low resistance to clothianidin. Low levels of reduced sensitivity to diafenthiuron were recorded in some regions.

In contrast to previous seasons, moderate to high levels of resistance to Group 1 insecticides was present in aphids from most growing regions. Of the 69 populations tested only 13% were fully susceptible to pirimicarb, with the overall industry average of pirimicarb resistance at 27.5%.

Further information

The GPA insecticide resistance management strategy is available from IPM Guidelines for Grains

Beatsheet posts with a focus on aphids: