|Crop Knowledge Master|
Aphis gossypii (Glover)
Jayma L. Martin Kessing, Educational Specialist
Ronald F.L. Mau, Extension Entomologist
Department of Entomology
Updated by: J.M. Diez April 2007
This is perhaps Hawaii's most common and destructive aphid. The cotton or melon aphid attacks a wide variety of plants. Economically important plants that are attacked include asparagus, avocado, banana, burdock, Chinese wax gourd, cucumber, edible gourds, eggplant, flowering ginger, green beans, guava, Hibiscus, hyotan, luffa, orchid, papaya, peppers, potato, protea, pumpkin, spinach, taro, togan, tomato, ti, watermelon and zucchini. Significant weed hosts include lamb's quarters, shepherd's purse, Malva and Bidens.
This insect is completely cosmopolitan, absent only in parts of Canada and Asia. It is know to be present in Australia, Brazil, East Indies, Hawaii, Mexico, South Africa, and the West Indies. Although scattered over the US Mainland, this aphid is far more common and injurious in the Southern and Western States. It was first reported on Oahu in 1909, and is now present on all islands throughout the State.
Aphids feed by sucking sap from their hosts. The undersides of leaves are preferred, other leaf surfaces and flower buds are its next choice, but the entire host may be covered when populations are large. Infested leaves often become cupped downwards and may appear wrinkled. Heavy infestations on some hosts may result in wilting. Young plants may have reduced or stunted growth.
Like other soft bodied insects such as leafhoppers, mealybugs, and soft scales, aphids produce honeydew. Copious amounts of honeydew, a sweet and watery excrement, may be produced. Honeydew serves as a medium on which sooty mold grows. Sooty mold blackens the leaf and decreases photosynthetic activity (Elmer and Brawner, 1975). When found on the fruit, honeydew and sooty mold reduces the marketability of the fruits. Growers respond by washing fruit before marketing them. Unfortunately, fruits often becomes unmarketable or of a lower grade because the fungus is difficult to wash off. Honeydew is also fed on by bees, wasps, ants and other insects, which may provide protection for the aphids from natural enemies.
Aphids vector many plant diseases which cause substantially greater losses than damage caused by direct feeding injury. This is often the most damaging feature of an aphid infestation. The melon aphid is an important vector of over 50 plant viruses. It is able to vector both P (PRSV-P) and W (PRSV-W) strains of Papaya Ringspot Virus. PRSV-P manifests itself on papaya. PRSV-W does not infect papaya, but does infect cucurbits and watermelon. PRSV-W is also called Watermelon Mosaic Virus 1 (WMV-1). This aphid also transmits Watermelon Mosaic Virus 2 (WMV-2). Cucumber Mosaic Virus (CMV) is transmitted by more than 60 species of aphids, and the most significant vector is the melon aphid. CMV can be acquired in 5-10 seconds and be transmitted in less than 1 minute. The ability of CMV to be transmitted declines after about 2 minutes and is usually lost within 2 hours (Francki, et. al., 1979). The melon aphid also vectors Celery Mosaic Virus.
Both apterae (wingless) and alate (winged) aphids are able to transmit viruses. Nonpersistent transmission occurs when the virus is taken up into the aphid's mouth while feeding on an infected plant and transferred to a healthy plant during the next feeding or probing of mouth parts. This process may require less than a minute. The virus reproduces in the plant and the aphids simply aid in transporting the virus.
Since winters in Hawaii are mild, there is no need for an over wintering egg stage. Reproduction does not involve mating and egg laying. Females give birth to live female nymphs. As a consequence of this type of reproduction, populations are composed solely of females and there are no males present. There are many generations of this aphid throughout the year in Hawaii.
In temperate regions this aphid over winters as eggs. The shiny black eggs are often laid on the bark of fruit trees. Females do not lay eggs in Hawaii.
This insect has four nymphal stages separated by molts. Each stage lasts from 1-3 days for a total nymphal period of 4-12 days. Nymphs resemble adults except for their smaller size. They do not have wings.
Adult melon aphids are soft bodied insects. They are pear shaped and range from 1/16 to 1/4 inch in length. Color varies from yellowish green, to brownish green, to almost black. Adults are smaller and paler in high temperatures. Adult females produce 8-22 young per day.
Melon aphid adults are generally wingless. Adult aphids generally remain wingless until high population densities are reached. A high population density induces the production of winged individuals which can migrate to new food sources.
Dry weather conditions are favorable to aphids. Heavy rainfall decreases population sizes.
There are several beneficial insects that help to control aphid populations through parasitism and predation. Parasites to this aphid found in Hawaii include Aphelinus gossypi (Timberlake) and Lysiphlebus testaceipes (Cresson). Some of the predators include Chrysopa spp., Nesomicromus vagus (Perkins), Zelus renardii
(Kolenati), Platyomus lividgaster (Mulsant), Coelophora inaequalis (Fabricus), Allograpta obliqua (Say) and Leucopis nigricornis (Egger).
Insecticides should be used sparingly and in conjunction with other non-chemical control methods to decrease the development of resistance. Various aphid populations in Hawaii were studied for their susceptibility to endosulfan, esfenvalerate, methomyl, and oxydemeton-methyl (Hollingsworth, et. al., 1994). The study found endosulfan as the best choice for aphid control. However, the sites with the highest levels of resistance were also the sites with the highest use of endosulfan.
There is no listing for endosulfan and oxydemeton-methyl has been delisted as of April 2007.
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