Garden aphids, also known as plant lice, include many different species in the Aphidoidea insect family. Their most common colors are green and black, though brown, reddish-brown, and gray aphids inhabit some parts of the country.
Aphid eggs overwinter attached to plants, then hatch as nymphs in the spring. Then, in the fall the nymphs will lay eggs that contain some male aphids. These males then mate with the nymphs to produce the eggs that will overwinter and start the next generation of aphids. Mature aphids lay three to six eggs per day. The rapid asexual reproduction cycle during the growing season is what leads to the rapid and widespread infestation so familiar to many gardeners. Aphids suck the sap out of tender plant's shoots and leaves using beak-like mouths, injecting the leaves with their saliva as they do so.
The damage to plants is twofold: drinking the sap can weaken the plant and injecting the saliva can spread diseases from plant to plant. In addition, aphids excrete a sticky, clear substance called "honeydew" which commonly fosters the development sooty mold. Sooty mold is unsightly and interferes with the plant's ability to photosynthesize. Because aphids are so tiny, sometimes the first sign that massive infestation is pending is the sign of many ants on your plants.
The honeydew secretion is a much-prized food for ants, so when you see many ants on plants, there is a very good likelihood that aphids are also present. Aphids can weaken a plant, stunt its growth, cause leaves to curl or wilt, and delay fruit or flower production. There are a number of non-chemical ways to combat or discourage aphid infestations. Aphids are easily killed by standard chemical pesticides. In spring, the eggs hatch and the aphids migrate onto their summer host when available.
These female aphids can reproduce without mating and hold eggs in their bodies to give birth to live young. By eliminating mating and egg-laying, aphids have shortened their life cycle and increased their reproductive capability.
Throughout the summer, wingless females predominate, but winged forms may arise when populations become too large for the available food source.
In late summer, in response to the shortened day length, wingless females and males are produced for the purpose of mating and laying of fertilized eggs that will survive adverse winter conditions. Because of the spotty nature of infestations, a number of plants in several areas should be examined for aphids. Examine the terminals of 15 consecutive plants or other sample unit and rate the plants as infested or uninfested. Repeat checks at weekly intervals to determine the need to treat.
Cultural: Predators such as ladybird beetle adults and larvae, green lacewing larvae, syrphid fly larvae, and several parasitic wasps all help reduce aphid numbers when insecticides are not used. Heavy rains help dislodge aphids from the plant and, during periods of high humidity, fungal diseases may greatly reduce populations.
The remarkable reproductive capacity of the aphid normally overcomes the effects of natural controls in spring when cool temperatures hinder the development of natural enemies. These natural controls are most effective in the warmer weather of summer and fall. Chemical : Treat with an insecticide when threshold levels have been reached.
Keep in mind however, that green peach and melon aphids have shown resistance to several insecticides. In particular, resistance to organophosphate insecticides has been reported. Ask Your Gardening Question. We teach, learn, lead and serve, connecting people with the University of Wisconsin, and engaging with them in transforming lives and communities. Connect with your County Extension Office ». Find an Extension employee in our staff directory ».
Facebook Twitter. However, after several generations there can be a lack of space on the host plant. This triggers the birth of a generation of winged aphids, which can migrate to other hosts. Some species of aphid develop only on plants of a particular species. These types of aphids are called monoecius. The most common species that attack crops are heteroecious aphids.
Heteroecious means that they feed on different plant species. Heteroecious aphids that reproduce sexually at least once in their lives start their cycle when the winter eggs hatch on the primary host.
The primary hosts are usually annual weeds, shrubs or trees. A couple of parthenocarpic generations reproduced without fertilization then give rise to a generation of winged females that migrate to the secondary host. This is usually a cultivated plant. In this new environment the aphids reproduce asexually for several generations of females until the arrival of autumn, when there is a generation of winged males and females which return to the initial host plant and lay fertilized winter eggs, closing the cycle again.
Aphids are among the most feared pests among growers in temperate regions. What kind of damage can they do? The removal of phloem sap for food weakens the plant and causes a metabolic imbalance, twisting of the leaves and, in extreme cases, leaf loss. Leaf loss affects the quantity and quality of the final harvest. They also introduce toxins into the plant, systemically altering its development. The honeydew secreted by the aphids is an ideal culture medium for various fungi which form a barrier on the leaf, stopping it from taking in all the light that hits it.
But the most harmful consequence for the crop is the transmission of viruses. Aphids can transmit dozens of viruses from a diseased plant to healthy in few seconds, especially through the winged generation. The biggest problem with viruses is that there is no remedy for them, so that the infection of a plant that is not tolerant or resistant to the virus leads inevitably to a decline in the final production. The way to understand the degree of danger that virus transmission by aphids may represent and to choose an appropriate method of prevention is to understand the mechanisms by which these viruses are transmitted.
Potato plant damaged by the Potato Virus Y which is transmissible by aphids. When an aphid inserts its stylus to feed on a plant infected with a virus, some viral particles attach to the mouth parts or are ingested with the sap. This is what is called the acquisition phase and it lasts a few seconds to several days depending on the type of virus. When the aphid migrates to another healthy plant and inserts its stylus to feed, the inoculation phase begins.
Depending on the mechanism of transmission, viruses are classified as non-persistent and persistent. Non-persistent viruses can infect a healthy plant immediately. This type of virus transmission by aphids is the most difficult to avoid because once the aphids carrying virus have attacked the host plant, infection occurs immediately, with consequent loss of production.
Fortunately, however, the number of plants that can be infected is very low. The time within which an aphid with the virus can transmit the disease to other healthy plants is called the retention period, and for non-persistent viruses the retention time is a few minutes.
If the acquisition phase and retention time are longer, the virus is known as semi-persistent. For this type of virus, the solution is to prevent access of aphids carrying the virus to the crop and prevent the aphids that feed on infected plants from dispersing.
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