Aphid infestation on a leaf

How Aphids Make Plants Sick

Aphids are small pear-shaped insects that you may find on your plants. They are usually innocent but in large numbers can harm the plants they feed on. These insects can devastate plants by overfeeding and the infecting them with viruses. 


Aphids are very small (about 4mm in length) and can be winged or wingless. These insects have the ability to reproduce asexually, which means their colony numbers can soar quickly. Aphid feeding in moderation isn’t bad for plants, but an aphid infestation can lead to overfeeding, causing weakness of the plant. In addition to this, aphids are major carriers of plant viruses. These viruses can lead to poor plant growth and low crop yields.  

Plant viruses

A virus is a microscopic particle composed of only genetic instructions (DNA or RNA) protected by a protein coating. To replicate, viruses insert their DNA into host cells, infecting the host organism and usually causing harmful symptoms. Well-known viruses affecting humans include COVID-19, influenza, and HIV. Viruses can affect plants as well as humans and other animals. Symptoms of plant viruses may include lighter colors or alternating lighter and darker colored (mosaic) patterns. Other signs are leaf curling and stunted growth.  

Lightly colored, diseased leaf on house plant

Diseased and discolored leaf on a plant

Aphids as virus vectors

The aphid is a major spreader of viruses between plants. Similar to mosquitoes spreading malaria, aphids act as a vector by which the virus transfers from infected plants to new plants. The way they spread the virus is through their mouthparts. Aphids feed on the sap from infected plants and then contaminate new plants with their saliva.  

A large number of the viruses spread by aphids are called potyviruses. Plants affected by potyviruses include beans, carrots, lettuce, sweet corn, and sweet potatoes among others. More information about aphids transmitting viruses to vegetable crops can be found here

There are two ways aphids can spread viruses, persistent and non-persistent. An aphid must feed for many hours to get the virus in a persistent way. However, aphids spread most plant viruses non-persistently. For this way, the aphid can both get the virus and infect other plants in a very short period of time. This means aphids can quickly move from plant to plant and don’t have to settle on one to spread the virus. More information about persistent and non-persistent transmission can be found here

As well as spreading viruses, aphids have other harmful effects on plants, including feeding on their sap which can cause plant weakness and leaf loss and introducing toxins into the plant through their saliva. Aphids also attract fungi to the plants through their honeydew secretions which can block the sunlight from reaching the plants.  

How to prevent plant viruses from spreading

Aside from harming the thriving plants growing in your yard, plant diseases can have a poor impact on crop yields, resulting in major losses each year. As of now, there is no cure for virus-infected organisms. Strategies to combat plant viruses involve preventing the spread of the disease. 

Preventing the spread of viruses in plants usually means stopping an infestation of aphids through techniques such as weeding around the plants, covering crops with nets, removing crop remains, and planting species that can host predators of aphids. The aphids’ natural enemies are ladybugs and lacewings. Insecticides usually can’t stop non-persistently spread viruses. This is because the virus spreads as soon as the aphid lands on a plant. Insecticides also motivate aphids to move to new plants faster so they can avoid them.  

More information on this topic can be found at the following links: 

Transmission of plant viruses by aphid vectors

Aphids- Pests & Diseases 

Aphid-transmitted viruses in vegetable crops

Aphids in home yards and gardens