What percentage of wheat aphids carries the Barley Yellow Dwarf virus?
A team of K-State Entomologists and Agronomists led by Dr. Mike Smith, in cooperation with selected County Extension Agents, Area Agronomy Specialists, consultants, and producers, began a project in late fall 2012 to find out the percentage of wheat aphids in the state that carries a virus that causes Barley Yellow Dwarf (BYD). This three-year project is being funded by a grant from the Kansas Wheat Commission.
Barley Yellow Dwarf can be caused by several different viruses. The disease may cause serious problems in wheat, including death, especially if the young plants are infected in the fall. Spring infections are usually not as detrimental.
In either instance, the virus must be transmitted to the plant through the saliva of an infected aphid. Many different species of aphids may vector BYD, but in Kansas, it is most commonly attributed to bird cherry-oat aphids or greenbugs, the two most common wheat aphids in Kansas. Both aphid species oversummer in grasses including corn, sorghum, and volunteer wheat.
Aphids also migrate into Kansas from southern states in fall, late winter, and spring. These aphids suck juice from plants and, under stressful growing conditions, can be detrimental just due to their feeding. However, this is rare in Kansas, because lady beetles and parasitic wasps usually control aphid populations before they stress wheat plants directly. The main problem caused by aphids comes from their ability to transmit BYD. It only takes one infected aphid to transmit BYD to the plant.
Aphids become infected with the virus by feeding on an infected plant. BYD viruses have no known effect on aphids. Once the aphid is infected, she becomes a carrier and then can potentially infect other plants that she feeds on. Infected plants then become the reservoir and other aphids feeding on those plants can become infected. BYD spreads from there to infect more plants and more aphids, etc., until the disease has become a significant problem.
To determine what percent of the aphid populations have the potential to vector BYD into Kansas wheat, Dr. Smith’s team started by developing and testing a technique sensitive enough to detect the virus from individual aphids. The team then had to establish procedures to collect aphids and get them from the fields to the lab while still alive, because the virus degrades too much to be detected in dead aphids.
All of the samples collected during the spring of 2013 have now been tested and the first results from Dr. Smith’s team are presented in the map below. The blue numbers represent samples collected as assayed from each of those counties, and are the percent of the sample of aphids that are infected with BYD virus. For instance, Saline Co. has numbers 0, 17, 40, 90%. This means one sample had no virus, one sample had 17% infected aphids, another sample had 40% infected aphids, and the last sample had 90% infected aphids.
Since techniques and procedures have now been developed and tested, interested wheat cooperators will be able to submit samples of live wheat aphids to determine if they are carriers of BYD. Details on how and where to send live aphids will be available in the next 4-6 weeks as wheat planting gets underway. We want to wait until wheat fields have become established before collecting aphids this fall. This program will hopefully be expanded so many more aphids will be assayed to determine the potential for Barley Yellow Dwarf Virus all around the state.
Jeff Whitworth, Extension Entomologist