5. Aphids

5. Aphids -Toxoptera aurantii (Aphididae : Homoptera)
    Hosts
    • This aphid has over 120 hosts that include camellia, cocoa, coffee, Ficus, Hibiscus, Ixora, kamani, lime, macadamia, mango, mock orange, Pittosporum, pomelo and Vanda orchid.
    Damage
    • Aphids feed by sucking sap from their hosts. This often causes the plants to become deformed, the leaves curled and shriveled and, in some cases, galls are formed on the leaves.
    • In most cases the black citrus aphid is a minor pest of coffee wherever it is found.
    • This pest congregates on the tender young shoots, flower buds and the undersides of young leaves.
    • They are not known to feed on the older and tougher plant tissues On coffee it causes some leaf distortion and malformation of growth of leaves and tips of shoots.
    • It is often more a serious pest in nurseries.
    • Aphids Like other soft bodied insects such as leafhoppers, mealybugs and scales, aphids produce honeydew.
    • This sweet and watery excrement is fed on by bees, wasps, ants and other insects.
    • The honeydew serves as a medium on which a sooty fungus, called sooty mold, grows.
    • Sooty mold blackens the leaf, decreases photosynthesis activity, decreases vigor and causes disfigurement of the host.
    • When the sooty mold occurs on fruit, it often becomes unmarketable or of a lower grade as the fungus is difficult to wash off.
    • Aphids vector many plant diseases which cause substantially greater losses than caused by direct feeding injury.
    • This is often the most damaging feature of an aphid infestation.
    • The black citrus aphid is a vector of virus diseases of Coffea liberica, Coffea arabica var. bullata (blister spot) and Coffea excelsa (ringspot). Fortunately, aphid vectored viruses of coffee have not been reported in Hawaii.
    • On Citrus it is a vector of Citrus tristeza virus, citrus infectious mottling virus and little leaf and lemon-ribbing virus of lemon.
    • Presently, Citrus tritesa virus is the only known citrus virus that occurs in Hawaii.
    Biology
    • The development of this aphid is temperature dependent. At 77°F a generation (nymph to adult) may take as little as 6 days.
    • In cooler temperatures (below 59°F), a generation may take as long as 20 days.
    • Higher temperatures also reduce development rate, at 86û F populations of this aphid will sharply decline.
    • Generations are continuous throughout the year in Hawaii.
    Eggs
    • Eggs are not produced by this species.
    • Females give birth to living young.
    • Infested young shoots
    Nymphs
    • There are four nymphal stages of this aphid.
    • The first stage is approximately 1/36 inch in length and the last about 1/17 inch.
    • They are without wings and brownish in color.
    Adults
    • Only females are found.
    • They are oval, shiny black, brownish-black or reddish brown in color, either with or without wings, measuring 1/25 to 1/12 inch in body length and having short black-and-white banded antennae.
    • Winged individuals tend to have darker abdomens and be slightly thinner.
    • The incidence of winged individuals is dependent on the population density and leaf age.
    • Reproduction is partheneogenic or non sexual.
    • Females start reproducing soon after becoming adults.
    • They produce 5 to 7 live young per day, up to a total of about 50 young per female.
    Behavior
    • Newly born nymphs are found grouped together since mothers do not move about while birthing.
    • This is the only aphid with an audible stridulation or high piercing sound caused by the aphid rubbing two parts of it body together much like crickets.
    • Large colonies will produce this scrapping sound when they are disturbed.
    Management
    Non-Chemical Control
    • Several natural enemies of the black citrus aphid keep this pest under control.
    • Sometimes to the extent that insecticides are usually unnecessary.
    • Predators in Hawaii include Allograpta obliqua Say, Chrysopa basalis, Chrysopa microphya McLachlan, Coccinella inaequalis Fabricius, Coelophora inaequalis, Platyomus lividigaster Mulsant and Scymnodes lividgaster.
    • The parasites in Hawaii include Aphelinus semiflavus Howard and Lysiphlebus testaceipes (Cresson).
    • There are many other predators and parasites to this pest throughout the world.
    • This pest is also controlled by the entomogenous fungus Acrostalagmus albus.
    Chemical control
    • If chemical control becomes necessary either insecticidal oil, or a synthetic aphidicide (insecticide) may be used.
    • Chemical control should only be applied at the first signs of damage during periods of flush growth.
    • Flush growth (young red leaves) on coffee should be completely moistened after application of chemicals.

Last modified: Monday, 6 February 2012, 9:16 PM