Photo 2. Curly-top symptom on basil caused by large numbers of aphids feeding on the underside of young leaves.
Photo 3. Crazy ants tending aphids for their honeydew. The ants keep predators and parasitoids away and defend the aphids from their natural enemies. Winged aphids can be seen in the lower part of the photo.
Photo 4. Ladybird beetles feeding on aphids on maize. The yellow "worm-like" creature in the centre is a syrphid larva - the adults are hoverflies.
Photo 7. Syrphid larvae feeding on large numbers of aphids on maize. They are the larvae of hoverflies
Melon or cotton aphid. There are many aphids attacking a wide range of crops; Aphis gossypii, described here, is common in Pacific island countries.
Worldwide. In tropical, sub-tropical, and temperate regions. Asia, Africa, North, South and Central America, the Caribbean, Europe, Oceania. Aphis gossypii is recorded from American Samoa, Australia, Cook Islands, Fiji, French Polynesia, Guam, Kiribati, Marshall Islands, Federated States of Micronesia, New Caledonia, New Zealand, Niue, Northern Mariana Islands, Papua New Guinea, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu, Vanuatu, and Wallios & Futuna.
Aphids occur on many crops, ornamentalsand weeds; they are common on cucurbits (cucumber, melon, watermelon) and taro. They are also found on banana, bean, capsicum, chilli, citrus and eggplant.
Males are rare or not produced in tropical countries. Eggs are not laid. Females give birth to living young without mating. The young are adult in 4-7 days, after moulting four times. They then produce four to six young a day, up to 50 each. Because of this method of reproduction, populations grow rapidly, with many generations in a year.
Spread occurs by the winged forms of the aphid, and also long distance in winds. Spread also occurs associated with the international movement of plants and plant parts for food and propagation.
Aphids cause direct and indirect damage:
Look for groups of round, green (some may be light green, others dark green, almost black) insects on the underside of young leaves, on shoots and buds (Photo 1). They are about 1 mm long, with long antennae about the length of the body, and two tubes at the rear called "cornicles". Sometimes, winged forms occur, up to 2 mm long with prominent veins (Photo 3). It is difficult to see the detail of the body with the naked eye. Look for ants, they are often present, tending the aphids for their honeydew.
Aphid predators and parasites usually keep populations low. The most common are ladybird beetles (adults and larvae) (Photos 4,5&6), syrphid fly larvae (Photo 7), lacewing larvae, and tiny parasitic wasps that lay their eggs in the adult aphids. The wasp larvae develop in the aphids eating the inside parts and turning the aphids into empty shells, called "mummies" (Photo 8). Two impoprtant parasitoids are Lysiphlebus testaceipes and Aphidius colemani. Both exist as a number of different strains, so it is important to match the strain with the aphid strain and the environmental conditions.
Note, ants tend aphids for their honeydew. By doing so, they protect them from the activities of parasites and predators. To manage aphids, it is important to remove the ants, so that biological control can operate.
If ants are present, find the nest, and if not too close to the plant with aphids, destroy the nest with boiling water. Without ants, predators and parasites may bring about natural control.
AUTHORS Helen Tsatsia & Grahame Jackson
Information from Waterhouse DE (1998) Biological control of Insects: Southeast Asian Prospects. ACIAR Monograph no. 51, 548pp. Photo 6 Graham Teakle. Canberra, Australia. Photo 8 Caroline Smith. University of Tasmania, Australia.
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 for the Pacific Community.
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