Insect and Related Pests of Foliage Plants
Aphids
Aphids and Biocontrol in Greenhouses and Nurseries
Aphids are a major insect pest of plants in greenhouses and nurseries. There are thousands of aphid species (>4000) in the world. Most of the economically important aphid species are polyphagous, but the norm for aphids is host specificity. Most species (ca. 3,500) are considered to be host-specific. The most common pest species include Myzus persicae (the green peach aphid, Figures 1 & 2), Aphis gossypii (the melon or cotton aphid, Figure 3), and Macrosiphoniella sanborni (the chrysanthemum aphid Figure 4). Promising biological controls have been identified that can be used to reduce plant losses and pesticide use.
Knowledge of aphids and biological controls is key to the use of these techniques. Aphids are soft-bodied, pear-shaped insects generally less
than 1/8 inch long. They feed by piercing-sucking mouth-parts and often can be found feeding on stem tissue of infested plants. Major foliage plant hosts of aphids are Aphelandra, Dieffenbachia, Gynura, Hoya and Schefflera.
Frequently the undersides of developing leaves are infested, and feeding causes distorted or stunted leaf development. Alert nursery personnel can often detect white skins shed by the developing aphids (see figure on the left below) on upper leaf surfaces. These shed skins are often the first sign of infestation. The green peach aphid, illustrated in this slide infesting the lower leaf surfaces of Aphelandra is one of the most common species found in commercial greenhouses.
In greenhouses aphid populations, most individuals are wingless, but when colonies become dense, winged forms are produced which disperse within the greenhouse and establish new infestations. Infestations are often first noticed on plants adjacent to greenhouse vents or evaporative cooling pads, as these are the locations where winged migrants frequently gain entry. Under such conditions, winged forms caught in air currents are rapidly spread throughout greenhouses. Under greenhouse conditions aphid populations are all females, with each producing living young. Multiplication rates are greatly increased by the higher temperatures common within greenhouses.
During most of the year in Florida, aphids give birth to living young.
Figure 3: Melon aphid adult.