HortFACT
Identification
Adults of both species are of two forms, wingless and winged.
BLUEGREEN LUCERNE APHID. Wingless adults are usually 2-4 mm long, dark green, and have a waxy appearance. The antennae, legs, and siphunculi (posterior projections) are uniformly brown or pale green. Winged adults are very similar to the wingless form, but have two pairs of wings that at rest extend beyond the hind end of the body. The area surrounding the base of the wings is normally pale brown.
PEA APHID. Wingless adults are similar in appearance to those of the bluegreen lucerne aphid, but differ from them as follows. They are usually 4-5 mm long, green, and have a shiny appearance. The antennae are pale green or brown, but always have a dark band at the joint of segments 3 and 4 (approximately one quarter of antennal length from the head). The other joints in the antenna are also usually banded. There is normally a dark band at the middle joint of each leg, which is otherwise pale brown or green, and the tips of the siphunculi are usually dark. As in bluegreen lucerne aphids, winged pea aphid adults are similar to the wingless form apart from having two pairs of wings. They differ from winged bluegreen lucerne aphids in having the area surrounding the wing bases pale green.
The nymphs (young stages) of both species resemble the wingless adults, but are smaller and pale green. First-instar (first growth-stage) nymphs are approximately 1 mm long, whereas older nymphs are almost as big as the adults. Aphids pass through four instars before becoming adults. Some pea aphid nymphs can be distinguished from those of the bluegreen lucerne aphid by having dark bands on the antennae, but otherwise they look identical.
Host plants
Both species are pests of many legumes. The bluegreen lucerne aphid attacks clovers, lentils, and trefoils, and is a very serious pest of lucerne in New Zealand, Australia, and California. It can occur in large numbers on white clover, but its impact on pastures is not well known.
The pea aphid is known to attack sweet pea, broad bean. red and white clovers, and some vetches and trefoils. It is a serious pest of lucerne, and can cause severe damage to peas (hence its name).
Damage
Both species suck juices from their hosts, and therefore reduce the vigour and production potential of the plants.
The bluegreen lucerne aphid injects a toxin (poison) into the host plant while feeding. In lucerne this often causes premature ageing of the leaves, resulting in heavy leaf fall and reduction in the quality of the remaining leaves as food for livestock. Other symptoms include yellowing or curling of leaves and stunting of stems. The toxin often has long-term effects on the ability of the lucerne plant to regenerate after harvest, and can ultimately reduce its life span.
The pea aphid does not produce a toxin, but it too can have long-lasting adverse effects on its host plants because it is a carrier of many important plant disease viruses. After feeding on an infected plant, the aphid may transfer the virus it has picked up to plants on which it subsequently feeds.
Distribution
The bluegreen lucerne aphid originated in central Asia. Though first recorded in Japan in 1937, it has appeared in California, Australia, and New Zealand, becoming a major pest in all three countries. First recorded in New Zealand in 1975, it is now found throughout both main islands.
The pea aphid is widely distributed around the world, but is not present in Australia. In New Zealand it has been found as far south as Otago; and populations attain pest proportions throughout the North Island.
Life cycle
| Immature Nymphs |
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| Nymphs | |
| Adult | |
| Winged Adult |
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| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
Summer. In summer the development of both species is very similar, though considerably influenced by temperature. At 20-25oC first instar nymphs grow and moult four times to become adult females after approximately 7 days. Males do not occur in summer. The females are parthenogenetic (i.e., do not need to mate), and bear live young. They can produce young 1 day after maturing, and then 5-15 per day for approximately 7-10 days. At temperatures below 12oC development is very slow, and females may produce young for more than 6 weeks. The summer life cycle is shown in the chart.
Winter. In cold climates both males and females are produced, mating occurs, and overwintering eggs are laid. The New Zealand pea aphid has been found to enter this winter life cycle in the laboratory, but it has not yet been seen to do so in nature.
R T. HILL.