Aphids, also commonly called plant lice, belong to the family Aphididae. Aphids are one of the top major pests for the home gardener and crop growers alike. This is a pest that can be found world-wide. There are very few ornamental plants, also some trees and shrubs that are unaffected by this pest.
Depending upon which species you have, aphids can come in an array of different colors. You may see green, brown, brown-black, pink, yellow or even red bodied ones. Most aphids are monophagous, which means that they feed on only one type of plant and in some cases are named after the plant they feed upon.
Aphids are slow moving insects, with soft bodies. The soft bodies are because most of this particular species do not have a waxy coat covering to protect their bodies , which helps in their elimination from natural and unnatural elements.
If you look closely at an aphid, you will notice that aphids have a pear-like shaped body, with the bulging area at the rear of the insect. They range from 1/16" to 1/8" ( 4-8 mm) long. From the front of the body, two long slender antennae are easily seen.
Near the rear end of the abdomen, projected are two tube-like appendages called cornicles. It is this pair of cornicles that distinguishes aphids from other insects. When a parasitoid, ( an insect that will lay it's eggs in another insect, killing it when the larvae hatch) is noticed by the aphid, these cornicles will emit a defensive type of pheromone (smell) alerting the neighboring aphids of danger.
Adult " Stem Mother" aphids with nymphs.
When an aphid detects a predator, usually it will try to fall off or jump to another area for protection. Also there are some aphids which are called "soldiers." These soldier aphids are strictly for protecting the colony. Soldier aphids will not reproduce , nor will they feed. They serve one purpose and one purpose alone, that of guarding.
Most aphids can produce several parthenogenetic generations a year. Parthenogenetic means that these insects are asexual. They do not need a male to mate with. They give live birth to the next generation of aphids and are commonly called "stem mothers." While aphids are parthenogentic, they are also viviparous ( giving live birth during the spring and summer) and oviparous ( females mating with a male and laying eggs in fall) during the fall.
It is this ability to produce live births that can cause a single aphid to rapidly become a destructive population in a matter of a few days. Generally, a single aphid will give birth to 10-12 live nymphs a day. Each one of those nymphs, over the course of a two day period, will molt, shed it's skin and become an active birthing adult immediately. Within a one week period a single adult aphid has now produced a colony of several thousand aphids. It is interesting to note that due to genetics, those eggs that are overwintering in the ground, are already developing the embryos of the daughters and the granddaughters and so on of each new generation inside their bodies even before the nymphs are hatched.
When populations of aphids build up to a significant number, birth will then be given to nymphs who will grow up to be winged adults. These winged adults can either fly to neighboring plants and start the reproduction of another colony or they will try and climb to the highest point on a plant and try and catch a wind current to fly on.
Being almost microscopic and light weight, they can travel great distances on these wind currents which makes containment of this species nearly impossible. They do most of their flying during the day preferring to feed at night when the plants are doing their most active growth and the nutrients they seek are abundantly flowing. These winged aphids are especially looking for plants that give off a yellowish-greenish color. Plants that are unhealthy, sick and diseased showing leaves with these colors are very attractive to them.
Insects can feed in many ways. Some prefer chewing,some rasping and some sucking, or a combination of both. Aphids feed by the sucking method. Aphids have a proboscis (mouth-part) from which a slender stylet (looks like a long slender needle) protrudes out from proboscis when they want to feed. Some types of aphids will feed intracellulary. This means they will stick their stylet between the cell walls to feed. Others like to directly pierce through the center of the cell and these are called intercellular feeders.
Which ever way they prefer, what the aphids feed upon is the phloem, or sap, of the plant. The phloem moves carbohydrates in the form of sucrose (sugar) as food for plants to feed upon. When the aphid finds a particular cell it wants to feed upon, it does not immediately just start sucking the sap.
First it has to stiffen the stylet. A special chemical liquid is produced in the body that will make the stylet hard and stiff. Then the aphid will inject some of its own saliva into the cell. The aphid saliva kind of shores up the cell walls to keep it from collapsing on the aphid during puncture of the wall. Even after securing up the cell wall, it can take as long as a full day or longer before the aphid will actually be able to start sucking sap from the plant. This long process to secure food is the main reason that the aphids are so slow moving.
Some aphids are vectors of plant diseases. During feeding as the aphid is collecting sap, some of that sap is regurgitated back into the stylet and back down into the cell. This is how the aphids vector viruses from one one plant to another. Some aphids are only able to vector a viral plant disease for a very short period of time, while some aphids contain the genetic ability to pass the viral disease on to their young and future generations.
Removal and disposal of plants with viral infections will help to keep aphids from infecting other plants.
One of the by-products from the aphids feeding is called honeydew. This excretion from the anus is the removal of excess sugars from the body. The honeydew secretion causes many problems. It not only makes the surface of leaves sticky, but it also promotes the growth of an Ascomycete fungi commonly called "sooty mold." This black sooty mold blocks the light from the plant leaves preventing photosynthesis and the plants ability to produce nutrients to survive.
Another major problem caused by the honeydew excretion is the attraction of ants to the plants. Ants have a love-hate relationship with aphids. Ants are sugar lovers too and love nothing better than "farming" and "milking" aphids. Some species of ants will just walk behind the ants feeding on the honeydew on the plant parts. Others will walk up to the aphids and using a method only known to them, will gently stimulate the aphid from the underside ( milking) causing it to produce honeydew.
When a colony of aphids is building up and honeydew production slows down, the ants will pick up an aphid and carry it (farming) to another plant to feed. The aphid allows this with no harm to the ant. In the fall when when male and female aphids mate, the ants will gather the aphid eggs and carry them down into their nests for the winter.
In the nest the ants will care for the eggs and feed the nymphs right along with their ant young. As soon as environmental conditions are favorable in the spring, especially when new plant shoots are emerging, the ants will carry the aphids back out of the nest and place them on the plants to start feeding and reproducing. Some ants will even construct special structures to protect the aphids. That is the love part of the relationship.
This is the hate. If conditions are unfavorable or the aphid population gets too large in the ant nest. The ants will destroy eggs and aphids and feed them to their own young. If the ants also want to keep the aphids in a certain area and keep them from lying away, they will chew off the wings of the aphid to prevent its flight.
Ants usually are more easily seen on plants than aphids. If you see an ant hill forming in your garden or yard near your plants or crops, or ants climbing on them, scout your plants good as it usually means aphids are present or will be present. Now some plants have to have ants for pollination or for flower blossoms to open, but those particular cultivators are few and specific.
Controlling aphid populations is not easy. While most aphids feed up the upper parts of plants, the leaves and stems, some are also root feeders. These root aphids are not easy to spot and can do serious damage to your bulbs and the roots of many plants. With the feeding of root aphids, the bulbs and plants are opened up to fungal and bacterial diseases. You may see your plants become stunted, turn a yellowish color and have brown tipped edges.
There many ways biological and conventional to try and remove this pest. Some may work better in some areas than others. Some may not work at all. Before attempting any type of conventional control, one of the best things you can do is do is to capture the pest in a small clear bottle with a lid that can be sealed/filled with rubbing alcohol in it for proper identification. Also, before trying any method on a large area of your plants, do a testing on one plant or a few leaves and observe the reaction. Check to see if the aphids are dying and that damage is not sustained to your plant.
No one method is perfect or works all the time, but a combination can help to keep them in control.
There are many predators of aphids. Aphids generally appear before they do, but if you can use the simple basic conventional methods first, then these predators can take over for you.
Some of the best and easily purchased biologicals are those of the Green lace-wing bug, Lady beetles (Lady bugs) and the aphid eating gall-midge. These predators will increase their populations as needed to control the aphid populations. As they will lay eggs, it is best to try not to use any chemicals that would destroy them.
Other predators that will eat the aphids are, soldier bugs, spiders, syrphid flies, and damsel bugs.
There are also many parasitoid (an insect who will lay it's eggs in the aphid body and the larvae will kill it ) insects that attack aphids. Some of these are Tachinid flies, Braconid wasps and other types of wasps.
Promoting birds to your yard is also another type of biological control you can use. The picture below is that of a House Wren eating aphids off of a Lupine.
In the spring, it is a common practice when plants are emerging to apply a lot of nitrogen to your plants. High nitrogen applications can increase your aphid population. High nitrogen promotes growth of new tender shoots which are very tasty and full of sugars. try holding back on nitrogen until plants emerging or new seedlings are more able to withstand aphid attack.
Plant companion plants that deter the aphids, such as nasturtiums,garlic, chives, and petunias. Make sprays from crushing leaves of these plants and spraying on your plants.
Jet spray plants with dish soap product like Ajax. Make sure you rinse the plant leaves well afterward. Be sure to spray underneath the leaves that are tight knit, pull,apart and get down in cracks and crevices. Direct your spray down, not sideways. If you spray sideways there is the possibility that all you will do is spray the aphids off one plant and on to another.
With aphids being attracted to the color yellow, set up yellow dishpans of soapy water on the outskirts of your plants.
Wheat straw mulch instead of pine straw. Wheat straw has a chemical property that confuses the ants. It keeps the ants from emerging early in the season when plants are new and tender. This gives your beneficials time to emerge and be ready for when they do emerge. With the ants being confused and in the ground longer, food supplies wil get low and they will use the aphids as food for their young.
Aluminum foil mulches. Take pieces of cardboard and glue the foil to it and lay out. The cardboard will help keep the weeds from emerging and hold the foil in place. Reflection of the sun off the foil confuses the aphids and they don't know which way they are flying. This method basically only works when your plants are small. Once they get a lot of foliage on them the foil may become hidden.
Horticultural oils and insecticidal soaps can also be used. Make sure you read the directions, especially the temperature that the oil needs to be to be effective.
All photographs are courtesy of JRsbugs (Janet) at BugLife
All photographs are copyrighted to JRsbugs. Unauthorized copying is prohibited.