Abdomen - Two long tubes like exhaust pipes (cornicles) extend beyond the tip of the abdomen.
- ends in a short tail.
Head - Bears two slender antennae angled back over body. At least as long as body.
Antennae - Uniformly dark colour.
Immature aphids - Smaller and paler than adults.
In Australia, the BGA has been found only as asexually reproducing females. The aphids thrive in mild weather, so are most likely to be found from autumn to spring. During dry months the BGA survive in very low numbers on host plants, usually as winged aphids. In autumn they migrate to germinating annual legumes or lucerne. With optimal conditions large colonies can rapidly develop.
It has 4 instars.
Origin and History:
The Blue Green Aphid infests lucerne, lupins, Faba Beans, Canola and a wide range of pasture legumes including subterranean clover, white clover, red clover and annual medics. In lucerne and medics severe infestations cause stunted growth, leaf curling, yellowing and eventual leaf drop. The aphid usually infests the growing tips of the stem first and gradually work down the stem towards the crown as numbers build up. The amount of dry matter produced can be greatly reduced.
Clover pastures infested with BGA have a patchy burnt appearance often known to be incorrectly attribute to moisture stress. Leaves wilt and turn over to show their pale underside. If infestations remain unchecked the leaves turn brown at the edge and wither until finally large patches of pasture completely dry off. The BGA are found widely dispersed under the canopy of clover swards, particularly on flower/burr stalks. Along with reduced dry matter production, seed yields of annual species can be reduced from 20-30%. The extent of damage varies, paddocks closed for seed production and subsequently with a greater amount of feed on offer are most susceptible.
In lupins BGA are found in buds and flowers in small colonies. Direct feeding of large numbers, slows growth, distorts flowers and reduces pod set and fill. Virus transmitted by BGA can cause a range of symptoms to lupins including stunted growth, leaf yellowing and characteristic 'shepherds crook'.
In lucerne, they cause shortening of the internode, leaf puckering and death of young seedlings.
Management and Control:
Sowing of resistant or tolerant cultivars of Lucerne, medic, clovers or lupins can play a major role in overcoming economic losses.
In Lucerne - 100 aphids per 5 m sweep of an insect net for fresh regrowth and increasing to 400 aphids for older stands. For seedlings - 1-3 aphids per plant is usually worth spraying.
For established plants - 20-40 aphids per stem is usually worth spraying.
On lupins, if 30% of the growing tips have more than 30 aphids then
a) on varieties with moderate or greater aphid tolerance. apply a single spray, one to two weeks after reaching this threshold or
b) on varieties with less than moderate tolerance, apply a spray immediately and a follow up spray in two weeks time if necessary.
Varietal Sensitivity to Aphids.
Wodjil Yellow Lupin
On Faba Beans and Lentils, aphid infestations probably have to be very heavy or early before it is worth spraying.
Parasitic wasps, hover flies, lady birds, damsel bugs, lace wings and fungal (entomophtora) disease are biocontrol agents. Biocontrol agents are only effective when aphid numbers are low. Under optimum conditions where aphids have the ability to rapidly multiply the use of insecticides maybe necessary.
There is a number of insecticides available for BGA control. Use of chemicals that are solely aphicides and 'soft' of beneficial insects in important to encourage biocontrol agents.
Francoise Berlandier, Agriculture WA (pers. comm.)
David Pfeiffer, Agriculture WA (pers. comm.)
Collated by HerbiGuide. Phone 08 98444064 for more information.