Aphids

Order: Homoptera
Family: Aphididae

Identification: The term 'aphid' is used to describe a number of different species coming in all shapes, sizes and colors. Adult aphids can be winged or wingless depending on many different factors. Aphids are small (~5mm), delicate, pear-shaped insects. Characteristically, aphids have piercing-sucking mouth parts. These are held underneath the body and resemble a beak or a needle. Aphids have a rather useful set of structures called cornicles located at the rear of the body. They also come in all shapes and sizes but will look like two tubes sticking out of the aphids back. These structures are used to exude honeydew and wax.

Life History: As most people have unfortunately experienced, aphids have an unusual capacity for reproduction; aphids are baby factories. In some species, it is possible to have an aphid inside an aphid inside an aphid; all are ready to reproduce as soon as they hit the outside world. The cabbage aphid can produce as much as 100 babies with in a month, and each of those babies has the same potential. Aphids can have an extremely complex seasonal life cycle that can involve hundreds of different host plant species. For example, the green peach aphid must overwinter on Prunus hosts as an egg. Eggs hatch and females start to reproduce for about 4 generations until May. Winged forms are produced and the aphids fly to spring and summer hosts that can, in Washington, consist of over 200 plant species! In some cases, the cue to grow wings can be in the form of physical abuse. If an aphid is kicked enough times by other aphids, it produces alate (winged) offspring that will disperse into much less crowded conditions. Usually, the winged forms are determined by day length or host development. Asexual generations are cloned on the respective host plants though out the summer. Males are not needed until the fall, when the aphids reproduce sexually for the overwintering eggs.

Damage: Aphids are different from most herbivores; instead of defoliating, they tap into the plants vascular tissue and steal all the nutrients being transported. Aphids are more like a plant parasite than a herbivore. Aphids can cause damage to our plants both directly and indirectly. Direct damage is produced by robbing the plant of nutrients and deformation of developing buds. Many developing buds and fruits will become wrinkled and deformed as the plant continues to grow. Heavy infestations will eventually cause death of the plant. Damage is also caused from the production of waxes and honeydew. Aphid excretions are a prime medium for growing sooty molds and mildew that can destroy fruits and foliage. These substances are excreted from the aphids' cornicles. Honeydew is often harvested by ants, so a good indicator of an aphid infestation is the presence of ant activity. To repay the aphids for their generosity, ants offer protection from other predators and parasitoids. Finally and most importantly, aphids are vectors of many plant viruses. The green peach aphid is known to vector as many as 300 viral diseases!

Control: Since aphids are so abundant, there are many predators and parasitoids that exploit them. The most famous are the lady bugs and lace wings; however, these can be difficult to recruit and keep around. There are many parasitic wasps that are specialized to feed on strictly aphids. So where ever you have aphids, you see that many of them are parasitized. When a wasp parasitizes an aphid, it becomes mummified. Inside the mummified aphid is a developing wasp larva that will emerge shortly as an adult to sting more aphids. Chemical controls can be in the form of very simple products. Oils and soaps are excellent to control and/or prevent aphid infestations when used at the right time. The most impressive form of chemical control is garlic. When I was studying aphids as a graduate student, I found that they would bail off my plants whenever I ate Italian. It took me a while to make the connection between my bad breath and the aphids' behavior. There are many different formulations of garlic available but surprisingly, most of the products I have worked with dissipated with in 12 hours of the application (especially on sunny days). Right when the application is made, the garlic stench is strong enough to make even garlic lovers gag. However, the smell does not persist very long and no residual garlic taste is left on the foliage or the fruit. Read the label on the product before using any garlic formulations on your garden to make sure that it states the persistence of the product and please do not use it for seasoning your food (it is a pesticide!