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Aphis citricidus (=Toxoptera citricida)
Brown citrus aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host Damage & Control
Identification & Distribution
Adult apterae of Aphis citricidus (previously Toxoptera citricida) are shiny, very dark brown to black, with dark siphunculi and cauda (see first picture below) (cf. Aphis spiraecola, which are yellow or green). The antennae of adult wingless forms and larger nymphs are not striped, but are dark on about the distal half of its length (cf. Aphis aurantii, which has black-and-white banded antennae; and cf. Aphis craccivora, which has the antenna dark on only the distal 0.3 of its length). The terminal process is 4.0-4.5 times as long as the base of antennal segment VI. The longest hairs on antennal segment III are 1.5-2.0 times the basal diameter of that segment (cf. Aphis aurantii, which has the longest hairs on that segment 0.5-1.0 times the basal diameter). The siphunculi are about 1.5 times as long as the cauda. The body length of adult Aphis citricidus apterae is 1.5-2.4 mm.
First image above by permission, copyright Sunil Joshi & Poorani, J. Aphids of Karnataka. (accessed 12/8/20).
Alatae of Aphis citricidus (see second picture below) have a shiny black abdomen. Antennal segment III is dark (cf. Aphis aurantii, which has antennal segment III mainly pale). The forewing has a pale pterostigma and a twice-branched medial vein (cf. Aphis aurantii, which has a very dark pterostigma, and usually a once-branched media).
Immature Aphis citricidus are a distinctive orange-brown (see two pictures below of colonies of the brown citrus aphid).
Aphis citricidus is mainly found on young growth of plants in the Rutaceae, although occasionally large colonies of aphids develop on young growth of other trees and shrubs. The main host is undoubtedly Citrus spp, where it rolls the leaves and stunts shoots sometimes causing significant damage. However, most damage results from transmission of the tristeza virus. Aphid colonies are ant-attended. When disturbed, the aphids may make stridulatory movements with their hind legs, but the sound produced is not audible. The species is anholocyclic in most parts of the world - but Komazaki (1988) recorded a sexual phase on Citrus unshiu in Japan, suggesting that is where the species originated. The brown citrus aphid is found in southern Africa, southern Asia, Australia, New Zealand, Pacific islands and subtropical and warm temperate parts of South America. More recently it has spread to important citrus-growing areas in Central America, the Caribbean and southern USA, as well as to Madeira, Portugal and north-western Spain. It has not so far reached the Mediterranean region nor the Middle East.
Other aphids on the same host
Damage and control
High populations of Aphis citricidus during bloom periods can cause direct feeding damage to citrus. But the major damage to citrus associated with infestations of Aphis citricidus is caused by transmission of Citrus tristeza virus (CTV or Tristeza virus). CTV is a closterovirus which causes possibly the most serious virus disease of citrus world-wide. More specifically it causes multiple disease syndromes, the most important of which are quick decline of trees on sour orange rootstock and stem-pitting in susceptible scions irrespective of rootstock. CTV transmission is thought to best fit the semi-persistent mode of transmission in which the virus is acquired and transmitted by aphids with feeding times ranging from several minutes to several hours, but usually not by brief probing. A number of studies have shown that Aphis citricidus is a relatively efficient vector of CTV when compared with other aphids that feed on citrus.
Historically, introduction of the brown citrus aphid has resulted in the rapid spread of CTV throughout entire citrus growing regions. The best examples of this are the virtual destruction of the citrus industry in Brazil and Argentina in the 1930s and 1940s (Knorr & DuCharme, 1951) and in Colombia, Venezuela and Peru during the 1970's (Lee et al., 1992). The brown citrus aphid was first detected in Florida in 1995, probably as a result of introduction on infested plant material rather than natural spread from the Caribbean. By the end of 1997, the entire Florida citrus production area had been colonized.
Halbert & Brown (1996, 1998) give an account of the introduction of Aphis citricidus into mainland USA, and also describe the different components for integrated pest management to achieve a measure of control over CTV. Components include cultural control (transition from sour orange rootstock to less susceptible rootstocks, protection of propagation sources, inoculum suppression), biological control, chemical control for protecting nursery stock and cross protection (deliberate infection with mild strain of CTV to suppress severe strains). A recent update is given in Batuman et al. (1995, 2020).