HortFACT
Identification
Adult females may be either wingless or winged.
The stout bodies of wingless (apterous) adults are about 2.0mm long and 1.0mm wide, tapering at each end. They are dull green to grey in colour and covered with a whitish waxy powder. There are several small black markings on the back, and at the rear of the body are two small upright projections called siphunculi. The head is small and dark with ruby coloured eyes and a pair of short slender antennae. The thin legs are about 1.5-2.0mm long, varying in colour from straw to black.
Winged adults, or alates have two pairs of strongly veined wings which, when held at rest, extend well beyond the rear of the body. In contrast to the wingless form, the whitish mealy powder is virtually absent. The black markings on the back are large and clearly visible giving the winged insect a striped appearance. The antennae are slightly longer than those of the apterae.
The immature stages or nymphs closely resemble the wingless form but are much smaller, about 0.5mm at birth. Nymphs pass through four instars before becoming adults. They are found together with wingless adults in colonies of various sizes on the plant.
Host plants
Cabbage aphids are found on all plants in the cruciferous family: cabbage, rape, swedes, turnips, broccoli, Brussels sprouts, cauliflower, kale, mustard and some weed species. It is the most common aphid found on these plants and usually the most abundant.
Damage
Aphids feed by sucking plant juices, causing yellowing and curling of leaves and seedheads, and wilting and stunting of plants, particularly during hot dry weather. Colonies of aphids can severely reduce the vigour and yield potential of a crop especially if it is being grown for seed production. Cabbage aphids also transmit a number of viruses within and between brassica crops. For example, they are important vectors of cauliflower mosaic and turnip mosaic viruses.
Vegetables infested with aphids are rejected for market (an economic loss to the grower) and heavily infected feed crops such as turnips and rape may also be unpalatable to stock.
Distribution
The grey cabbage aphid is cosmopolitan. It is present throughout New Zealand wherever cruciferous crops are grown, but occurs more frequently in the South Island.
Life cycle
 |
|
| Nymphs | |
| Adult | |
| Winged Adult | |
| Month | |
| Note: Coloured bars indicate periods of peak activity in each of the life cycle stages | |
All stages in the life cycle, wingless adults and nymphs, are present throughout the year. Female aphids are parthenogenic and viviparous, that is, producing live nymphs without mating. Males rarely occur but are similar in form to the winged female.
Although small numbers of winged (alate) aphids fly throughout the year, large numbers are produced in spring (October/November) and autumn (February/March) when the main dispersal flights to other crops occur. New colonies are then initiated by the winged aphids. Established colonies are made up of individuals of several generations of sedentary apterous aphids, with a single adult producing 22-26 nymphs. The rate of growth is dependent mainly on temperature, during summer development from nymph to reproducing adult takes 7-16 days, while m cooler winter conditions this period may be prolonged to 40-60 days. The life span of the aphid is usually about 28 days.
A.M. FERGUSON and H.E. BLAKE