Article 1-3 Pest Profile: Aphids
Aphids are major greenhouse pests because of their large host plant ranges, ability to produce high populations rapidly, ability to transmit plant viruses, their resistance to many commonly used insecticides and finally, difficulty in detection.
There are more than 4,000 species of aphids, but only a few of them are pests in the greenhouse. The most common aphids in the greenhouse are: GREEN PEACH APHID (Myzus persicae) and MELON/COTTON APHID (Aphis gossypii).
IDENTIFICATIONAphids are small (I - 3 mm), fragile, soft-bodied and pear-shaped insects generally found in colonies. Their antennae are approximately one-half the lengths of their body. The green peach aphid has long, laid-back antennae and bumps on the inside of the base, while the melon/cotton aphid has shorter, darker antennae without bumps. Color can vary (with temperature, season and population density) from green to rose pink (green peach aphid) and yellow, light to very dark green or nearly black (melon/cotton aphid). Aphids are distinguishable from other insects by the presence of a pair of cornicles or "tail pipes" on the rear of the abdomen. Green peach aphids' cornicles are the same color as their body and darker at the tip while melon/cotton aphids have entirely dark cornicles and they are always darker than the body. In the greenhouse aphids are usually wingless, but when the population density becomes great, young aphids develop wings and migrate to another area to begin a new colony.
LIFE CYCLEAphids in greenhouses are all female and give birth to more live females without mating. The fact that under greenhouse conditions adults give birth to live young, means that there are no dormant stages, such as eggs or pupae, which are less susceptible to insecticides. One adult can produce 50 to 250 young during her lifetime, depending on the host plant and its nutritional status. The nymphs can mature and begin reproducing in 7 to 10 days. The life expectancy of the adult can be from 7 to 21 days, making possible more that 30 generations a year in the greenhouse.
DAMAGEAphids feed by inserting their piercing-sucking mouthparts into the vascular system (phloem) of the plant and sucking out the sap. This causes discoloration, curling, crinkling and wilting of leaves, malformation and distortion of buds and shoots, leading to plant stunting and deformities, reducing the vigor of the plant. They also have the potential to transmit virus, which can cause further problems.
When feeding, aphids excrete honeydew, a sugar-rich, sticky substance, that coats leaves and flowers and which is a good medium for black sooty mold to grow. Molted skins also reduce the aesthetic value of ornamental plants. Aphids feed on all parts of the plant, but prefer tender young tissue. Green peach aphids often congregate near the growing tip of the plant, while melon/cotton aphids are more evenly distributed throughout the entire plant, making it harder to detect an infestation.