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Aphis ruborum adult.
Aphis ruborum adult.
Aphis ruborum nymphs on strawberry plan
Aphis ruborum nymphs on strawberry plant.

Adventive Aphid and Natural Enemy Found in Mississippi

By Sandra Avant
November 20, 2019

Agricultural Research Service (ARS) scientists and their colleagues have discovered, for the first time, an adventive—meaning it just arrived in a new locality—aphid species as well as an associated parasitoid wasp on strawberry plants in Stoneville, Mississippi.

While sampling for plant pests and natural enemies, Eric W. Riddick, a research entomologist with the ARS Biological Control of Pests Research Unit, found the aphid, Aphis ruborum,on cultivated strawberries in his research high tunnels—unheated greenhouses.  It's not supposed to be here, he said. The species has spread in Europe, north Africa, India, Pakistan, Chile, Argentina, western United States (Washington state) and Canada.

The aphid was found predominately on newly emerged, not fully developed leaflets of daughter strawberry plants in 2016, Riddick said. By 2017, aphids were observed on fully developed leaflets on mother plants. The occurrence of A. ruborum in Mississippi represents a new state record and the eastern-most established record in the United States, he added.

The study, recently published in the Journal of Insect Science, cites another discovery. In 2017, Riddick found mummified aphids, which signaled that a parasitoid wasp, Aphelinus varipes, had attacked the aphid. The tiny wasp, which is a beneficial insect, is not known to attack this species of aphid.

This is first time an attack by the A. varipes waspon the A. ruborum aphidhas been documented anywhere in the world, Riddick said. The wasp layseggs that develop inside the aphid, killing it. ARS scientists in Beltsville, Maryland, identified the aphid, and non-ARS colleagues at the University of Georgia and Agriculture and Agri-Food Canada identified the parasitoid wasp, using molecular techniques.

The aphid seldom uses cultivated strawberry as a host plant, Riddick said. However, it frequently attacks blackberries, damaging foliage. As it feeds, the aphid also injects a virus, which can cause plants to wilt and die.

The next step is to figure out where the aphid came from. It is possible that previously undetected populations of the aphid have survived on uncultivated plants (such as wild strawberry, dewberry or blackberry) in the landscape surrounding Stoneville. Riddick plans to conduct a small-scale sampling for the aphid on wild plants in areas around Stoneville and study the rate at which the aphid is being attacked by the parasitoid.

The Agricultural Research Service is the U.S. Department of Agriculture's chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.