Virus Pulls Bait and Switch on Insect Vectors(UNFINISHED)

This is a wingless morph of Myzus persicae aphid on squash plant. (Credit: Photo Credit: Kerry Mauck (courtesy of De Moraes and Mescher labs), Penn State)
http://www.sciencedaily.com/releases/2010/02/100201171758.htm

It was found that a common plant virus leads aphids to plants that infected. This is done by the plants making them more attractive but when the aphids taste the plant they move onto healthier plants. This rapidly spreads the disease.

This virus improves cues that the insects use to identify food. The virus elevates some aspects of traits that is already present in the plant. For example without changing the oder the virus elevates the oder cue. These type of host alterations has implicated beyond the basic agriculture, if pathogens can now alter their hosts to make transmission more efficient. It is believed they may be doing this through insect-transmitted human diseases such as malaria or dengue fever.

Some virus amongst plants entice the insects to visit there plants and fool them into believing that they are healthy, this them incorporates the virus into the insect's system. When the insects leave and find a new food source they transmit the virus to the new plant. This works only if the insect spends a decent amount of time feeding off of the infected plant. Researchers and looking into the cucumber mosaic virus because it is not persistent and the insects pick it up and transmit it from leaf to leaf by the first bite.

The researchers are looking at the cucumber mosaic virus because it is not a persistent virus. Insects pick up the virus when they take their first taste of leaf. When insects bite into a leaf the virus binds chemically to the mouth parts and releases when the insect feeds on another leaf. In most cases this only occurs to the first plants and not the ones afterwards. This then makes the virus a non-persistent virus.

The finding of this research was found in this week's online Proceedings of the National Academy of Sciences.

"Viruses like these (non-persistent ones) use a different system to ensure transmission," said Kerry E. Mauck, graduate student in entomology. "They have not been examined as closely as persistent systems."

The studies have investigated two species of aphids that transmit cucumber mosaic virus. This virus infects the entire squash family of plants. One of these species prefers squash but will also eats other things the other species prefer turnips but will also eat squash. The researchers developed a special insect arena that was developed to test the aphid’s responses to different plant odors. The studied showed that the insects could not see or alight on the plants so the result was they did not have color or taste cues. The insects could only access chemicals that the plants released into the surrounding air.

"We wanted to see where they aggregated most often," said Mauck. "They tended toward the plants that were infected rather than the healthy leaves."

They then tested the aphids to see which plants allowed them to reproduce the best. The results showed that the aphids reproduced less on the infected plants than they did on the healthier plants. The next step tested the aphids to see how long they would spend feeding on the infected or the healthy plants. The results showed that the insects spent more times on the healthier plants despite the increased odor cues that the infected plants gave out.

"We demonstrated that there were attraction cues combined with a repellant response when the plant was eaten," said Mauck. "We used two species of aphid to ensure that it was not a fluke that one aphid behaved this way."

Time studies where not done to see how many aphids actually visit sick and healthier plants over time. Studies were done and concluded that the infected plants produce more volatile chemicals than the healthier plants but are the same.

"If the viruses caused the sick plants to produce altered volatile cues, then the insects could learn how the sick plants smelled and avoid them," said Mescher. "Because the virus only increases the amount of chemicals, there may be no way for the insects to distinguish between sick and healthy plants until they feed on them."

The team of researchers are still working on similar questions that relate this study to human disease systems.

"We know that malaria-infected people are more attractive to malaria-transmitting mosquitoes," said Mescher. "We do not know if the same principles as in cucumber mosaic virus apply to malaria, but we are working on it."

"The U.S. Department of Agriculture supported this work.”