Photo 1. Adult, wingless, green peach aphid; the white remains of the skin of the last moult remain attached to two aphids.
Photo 3. Adults and nymphs of the green peach aphid, Myzus persicae, on sweetpotato. Note the brown tinge to many of the adults.
Green peach aphid
Worldwide. Asia, Africa, North, South and Central America, the Caribbean, Europe, Oceania. It is recorded from Australia, Fiji1, New Caledonia, New Zealand, Northern Mariana Islands, Solomon Islands, and Tonga.
Wide. Over 40 families are hosts. Peach, nectarine, plum and almond are the main hosts, but there are many vegetables, too: bean, cabbage, capsicum, lettuce, papaya, pea, potato, sweet potato, and ornamentals as well as weeds [(e.g., dock (Rumex), sowthistle (Sonchus), lambsquarters (Chenopodium) and pigweed (Portulaca)].
Adults and nymphs do the damage in three ways: first, they feed directly on young tender plant tissues, often drying out shoots, causing wilts and distortions; second, they produce honeydew which falls onto foliage and becomes blackened by sooty mould fungi; and third, they spread more than 100 viruses. However, although the importance of the aphid as a virus vector is well known in other parts of the world, very little is known about the aphid and its potential to spread viruses in Pacific island countries.
Adults are about 2 mm long, greenish-yellow, sometimes with a brown tinge (Photo 1-3). Adults may be winged or wingless. If winged, then the head and thorax - i.e., the segment that bears the first pair of legs - is black (Photos 4&5). The nymphs are similar to the wingless adults, except in size.
In tropical countries, males do not exist. Females give birth to living young without fertilisation. There are about 20 generations of the aphid per year. The average life cycle is about 18 days.
Spread occurs by the winged forms of the aphid, and also long distance in wind and storms. Spread also occurs associated with the international movement of plants and plant parts for food and propagation.
The impact of this aphid is that it spreads many important viruses. Some are "persistent" in that they multiply within the aphid and are spread during feeding for as long as the aphid lives; others are "non-persistent", do not multiply within the aphid and are lost quickly during feeding.
Some of the damaging viruses are potato leafroll, potato Y, beet western yellows, beet yellows, cauliflower mosaic, cucumber mosaic, lettuce mosaic, papaya ringspot, turnip mosaic, and watermelon mosaic. The green peach aphid is considered the most important vector of plant viruses in the world.
Look for the greenish-yellow aphids, tinged with brown, and the dark first segment on those with wings. However, in commercial crops, it is the presence of virus that is important, far more than the physical damage of the aphids. For this reason, aphids are trapped and tested for viruses.
Aphid predators and parasites usually keep populations low. The most common are ladybird beetles (adults and larvae), syrphid fly larvae, green lacewing larvae, and tiny parasitic wasps that lay their eggs in the aphids. The wasp larvae develop in the aphids eating the inside parts and turning the aphids into empty shells called "mummies". There are many parasitoids attacking the green peach aphid with, perhaps, species of Aphidius and Aphelinus, the most important. However, it is often the case that low aphid populations can still cause high virus incidence.
Most of the cultural control methods are aimed at controlling the viruses spread by the green peach aphid.
The green peach aphid is important mainly because it spreads viruses. This means that populations of aphids need to be kept very low, and that is difficult. It is particularly difficult to prevent aphids from spreading non-persistent viruses because they are spread very quickly. By the time the aphid has been killed by the pesticide, it has fed and infected the plant. Furthermore, aphids may be passing through the crop, checking the plants as hosts and in the process spreading viruses, and then moving on.
Where the aphids require time to acquire and spread viruses (persistent viruses), the use of insecticides can be useful. But note, that this aphid has shown an ability to produce populations tolerant to several insecticide groups, including organophosphates and pyrethroids.
AUTHOR Grahame Jackson
1Information from Swaine G (1971) Agricultural Zoology in Fiji. Her Majesty's Stationery Office. London; and CABI (2016) Myzus persicae (green peach aphid) Crop Protection Compendium (www.cabi.org/cpc); and Waterhouse DE, Sands DPA (2001) Classical biological control of arthropods in Australia, ACIAR Monograph no. 77, 560pp.; and from Myzus persicae (Sulzer) Entomology & Nematology. UF/IFAS, University of Florida. (http://entnemdept.ufl.edu/creatures/veg/aphid/green_peach_aphid.htm). Photos 1-6 Mani Mua, Sigatoka Research Station, Fiji.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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