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Aphis gossypiiHypericum aphid, Melon aphid, Cotton aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Colour Ant attendance Other aphids on the same host Damage & ControlIdentification & DistributionWingless females of Aphis gossypii are usually medium-sized and blackish green or dark green mottled with lighter green (see first two pictures below). In hot conditions or when crowded they are smaller, and these dwarf forms are a very pale whitish yellow (see third picture below). The dorsum has no dark sclerotized markings. The longest hairs on the third antennal segment are 0.3-0.5 times the basal diameter of that segment. The terminal process of the last antennal segment is 1.7-3.2 times the length of the base of that segment. The apical segment of the rostrum is 1.1 to 1.5 times as long as segment 2 of the hind tarsus. Marginal tubercles are only consistently present on abdominal tergites 1 and 7. The siphunculi are usually dark, but in the dwarf form they may be pale with dark tips. The siphunculi are 1.3-2.5 times as long as the cauda. The cauda is variable in colour from quite pale to dusky to quite dark but it is usually paler than the siphunculi and bears 4-8 hairs (cf. Aphis solanella and Aphis fabae, which have the cauda always dark like the siphunculi and bearing 7-24 hairs). The body length of adult Aphis gossypii apterae ranges from 0.9-1.8 mm.
Third image above copyright CSIRO under a creative commons 3.0 licence. Aphis gossypii alates (see fourth picture above) have 6-12 secondary rhinaria distributed on the third antennal segment and usually none on the fourth. Micrographs of whole mounts in alcohol are shown below.
The clarified slide mounts below are of adult viviparous female Aphis gossypii : wingless, and winged.
Micrograph of clarified mounts of aptera and alate, courtesy Favret, C. & G.L. Miller, AphID. Identification Technology Program, CPHST, PPQ, APHIS, USDA; Fort Collins, CO. The melon- or cotton-aphid is highly polyphagous and does not usually host alternate, reproducing all year round on its chosen host (see below for exceptions to this). In temperate climates it is most often seen in glasshouses on cucurbits (cucumbers and marrows) and begonias, and in gardens on ornamental Hypericum species. In the tropics Aphis gossypii is a major pest of cotton. It is distributed almost worldwide, and is particularly abundant in the tropics. Biology & Ecology:Life cycleAphis gossypii does not have a sexual phase in the tropics, nor in most of Europe. Some sexual reproduction may be taking place in southern France, although the primary host is unknown. Host alternation and a sexual phase occur more regularly in parts of east Asia and in North America.
In most of its geographical range Aphis gossypii consists of races, or divergent clones, which reproduce parthenogenetically.
Aphis gossypii often moves on to the flowers - the picture above shows them colonizing the flowers of Begonia grandis.
ColourAphis gossypii is quite variable in colour. The picture below shows a 'normal' coloured Aphis gossypii (mottled green) along with some darker aphids. It is possible that the darker aphids were also Aphis gossypii, since Aphis fabae is not recorded from this Hypericum species.
Alternatively this may be a mixed species colony. Our photos have revealed many examples of mixed species colonies, but these are seldom referred to in the literature and there has been little if any work on the dynamics of such colonies. Hill (1987) points out that many ecological studies have failed because of the inability of the observer/recorder to recognise a mixed species population. The most extreme colour form is the dwarf yellow form, shown below on a cucumber leaf in a greenhouse in Belgium.
Both images above by permission, copyright Marina Dhondt, all rights reserved. With this dwarf form the siphunculi are not black. As noted by Watt & Hales (1996), the siphunculi have just the apices the dark brown and the basal part yellow like the body. Production of yellow dwarfs in Aphis gossypii is very different from dwarfing produced through lack of nutrition. Although Aphis gossypii is well-known to show phenotypic plasticity in colour and size to an unusual degree even among aphids, the dwarf form seems to represent a distinct developmentally-programmed morph, in the same way as winged and wingless aphids do. Yellow dwarf Aphis gossypii have been observed in the field in Australia and in glasshouse conditions worldwide. Ant attendanceColonies may or may not be ant attended. One colony (see picture above) was found around a leaf petiole at junction of leaf and petiole of Hypericum androsaemum - no ants were attending the colony, but a Myrmica ant was feeding at an extra-floral nectary on the plant as shown in the picture below.
On other occasions ants were definitely attending the aphids, as shown above with a Lasius niger ant. Other aphids on same host:Secondary hosts
Damage and controlIn temperate climates Aphis gossypii is considered an important pest of greenhouse crops such as cucurbits, and ornamentals such as Begonia and calla lily (Zantedeschia aethiopica). Insecticide treatment may be recommended. Outdoors Aphis gossypii is a pest of Hypericum androsaemum and Hypericum inodorum. Leaves may turn yellow and on ornamentals the large amounts of honeydew and exuvia may look unsightly. Soap solution may be used to reduce numbers. In the tropics it is a major pest of many crops including cotton, cucurbits, coffee, cocoa, peppers and okra. Aphis gossypii is known to transmit at least 50 plant viruses.
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