Hypericum aphid, Melon aphid, Cotton aphidOn this page: Identification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Wingless females of Aphis gossypii are usually medium-sized and blackish green or green mottled with dark green (see first picture below). In hot conditions or when crowded they are smaller and are a very pale whitish yellow. 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 the length of segment 2 of the hind tarsus. Marginal tubercles are only consistently present on abdominal tergites 1 and 7. The siphunculi are dark. The cauda is usually paler than the siphunculi and bears 4-8 hairs. The body length of adult Aphis gossypii apterae ranges from 0.9-1.8 mm.
Aphis gossypii alates (see second 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.
Micrograph of clarified mounted aptera (first image) courtesy PaDIL. Copyright Rebecca Graham (Department of Agriculture, Western Australia) under Commons Attribution 3.0 Australian License. Alate micrograph (second image) 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. 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:
Aphis 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. Several unrelated plants are utilised as primary hosts.
Aphis gossypii often moves on to the flowers - the picture above shows them colonizing the flowers of Begonia grandis.
Colonies 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.
Aphis gossypii is quite variable in colour. The picture below shows a 'normal' coloured Aphis gossypii (mottled green) along with some darker aphids. It seems likely 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.
This particular colony had several predators actively reducing its numbers, including the syrphid larva shown above.
Damage and control
In 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.