Photo 2. Shiny black adult citrus aphids, Toxoptera sp., and reddish-brown nymphs on the back of a citrus leaf. Note the two syrphid larvae, predators of aphids.
Brown and black citrus aphids. There is confusion in these names with brown and black given to both species of Toxoptera by different authors. CABI has the common names as follows: Toxoptera aurantii is the camellia aphid, and Toxoptera citricida as the black citrus aphid. Some accounts give the common name for Toxoptera citricida as the black/brown aphid!
In this fact sheet Toxoptera citricida is the brown citrus aphid, and Toxoptera aurantii, the black citrus aphid.
Toxoptera species. Toxoptera citricida, brown citrus aphid (CABI-black citrus aphid); Toxoptera aurantii, black citrus aphid (CABI-camellia aphid).
Worldwide. The brown citrus aphid (Toxoptera citricida) is present in Africa, Asia, North and South America, Europe, Oceania. It is recorded from Australia, Cook Islands, Fiji, Papua New Guinea, Samoa, Solomon Islands, and Tonga.
Worldwide. The black citrus aphid (Toxoptera aurantii) occurs in Africa, Southeast Asia, North (Florida, Hawaii) and South America, Caribbean, Europe (restricted), Oceania. It is present in Australia, Federated States of Micronesia, Fiji, French Polynesia, Guam, New Caledonia, Northern Mariana Islands, Papua New Guinea, Samoa, Solomon Islands, Tonga, and Vanuatu.
The brown citrus aphid (Toxoptera citricida) occurs on citrus, and perhaps close relatives. There are unconfirmed reports of colonies on new growth of plants in several families. The black citrus aphid (Toxoptera aurantii) occurs on over 120 hosts, including citrus, cocoa, coffee, Hibiscus, maize, Vanda orchids and tea.
Adult wingless aphids vary in colour; some are black, others brownish-black or reddish brown (Photo 1). It is difficult to tell the two species apart in the field; a microscope is needed to see the colour patterns on the antennae and legs, as well as differences in other organs.
The reddish-brown nymphs mature in 6-8 days at 20-25oC (Photo 2). The nymphs pass through four stages before they become adults. The adults start giving birth soon after they are mature, producing 5-7 nymphs a day, and 50 in a life time. They exist in two forms: winged and wingless. Most adults in the colonies on young leaves are wingless; winged forms develop when aphid numbers are high (or the leaves are old and less nutritious) (Photo 3). The winged aphids leave the colony soon after they are mature. They can travel up to 30 kms.
Populations of the aphids increase very quickly compared to other species, because of their simple life cycle. In most parts of the world, there are only females, and these give birth to nymphs which are all female. The reproduction rate is so fast that several thousand aphids could be produced within 3 weeks from one female aphid, if none of them were destroyed by natural enemies.
The aphids damage citrus in three ways.
Of the different ways that these aphids cause damage, it is their ability to spread Citrus tristeza virus that is the most serious. Direct damage from infesting shoot tips is usually minor. It is more serious in nurseries than in the field.
One of the most devastating citrus crop losses ever reported came after the introduction of the brown citrus aphid into Brazil and Argentina: 16 million citrus trees grafted on sour orange rootstock were killed by Citrus tristeza virus.
Look for large colonies of aphids, with dark brown to black adults, 1-5-2 mm in length, and reddish-brown nymphs, on the flushes of citrus.
Several kinds of natural enemies exist, including parasites, predators and pathogens. These usually keep populations low. The most common are ladybird beetles (adults and larvae), syrphid fly (hoverfly) larvae (Photo 2), 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".
However, it is not known how good the predators and parasites are in lowering the populations of brown and black citrus aphids and reducing either direct damage or, more importantly, the spread of Citrus tristeza virus.
Not a useful method of managing this aphid.
If ants are present, kill them with boiling water, without damaging the crop plants, or use synthetic pyrethroids. Without ants, predators and parasites will bring about natural control.
AUTHOR Grahame Jackson
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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