AgBioResearch

Insects have long threatened human health and crops. The tools used to combat that struggle vary from the humble fly swatter to complex chemical sprays and the introduction of rival insects to prey upon the pests. Today, Michigan State University (MSU) AgBioResearch scientists continue to break new ground, developing and implementing new tools and methods to help better understand and combat insects.

MSU AgBioResearch entomologist Zsofia Szendrei has developed a plan to help Michigan farmers detect and fight against aster yellows, a chronic disease that afflicts over 300 species of herbaceous plants. In Michigan, the most common victims are celery and carrots. Growers in the state produce more than 59 million pounds of carrots, valued at over $12 million, and over 105 million pounds of celery, valued at almost $15 million.

Michigan ranks second in the nation for both vegetables, so aster yellows poses a significant threat to the state’s agricultural industry. The disease is spread by the aster leafhopper, a tiny yellow-green insect that feeds on sap from plant leaves. The pest itself does little damage to the plant, but as it feeds, bacterium-like organisms called phytoplasmas are injected into the leaves through the insect’s saliva. Once infected, the plants experience a multitude of symptoms, including stunted growth, deformed growth, greening of flowers and reddening of foliage, which inhibits photosynthesis.

About 5 percent of leafhoppers carry the disease. Small outbreaks have resulted in significant yield reduction averaging 25 percent in carrots and occasionally rising as high as 80 percent.The only effective means of preventing outbreaks in either vegetable or ornamental crops is to reduce the leafhopper population through strategically timed pesticide applications. To do this, growers must accurately estimate both the number of leafhoppers in their fields and the level of aster yellows they carry with them. Four years ago, Michigan vegetable growers came to Szendrei asking her to devise a predictive modeling system.

Szendrei partnered with a Michigan-based field scout, who travels virtually all of the celery acreage in the state to assess populations, to collect aster leafhoppers in the field. Once collected, the insects are stored in a portable freezer and delivered to MSU, where the high-tech work begins.

Using a molecular biology technology called polymerase chain reaction (PCR) — which cleans up and amplifies samples of genetic code, allowing researchers to analyze it with greater clarity — Szendrei’s team developed a laboratory procedure that tests leafhopper specimens quickly and estimates the level of aster yellows in a field.

“The original protocol we inherited from earlier scientists took days to get results,” Szendrei said. “Growers, on the other hand, can’t afford to spend that much time waiting to know if they need to spray, so we had to come up with a better solution for them.”

After two years of testing and with support from MSU Project GREEEN, the Michigan Vegetable Council and the Michigan Department of Agriculture and Rural Development, Szendrei’s team implemented the new, improved PCR method. Szendrei communicates the results via text messaging to growers all over the state to ensure that Michigan crops are protected.

“The growers have really embraced this,” Szendrei said. “Having this cutting-edge technology at their service and being able to receive accurate data in real time has made a big difference in their fields.”

Applying advanced technology to seemingly low-tech problems is not the exclusive province of plant science. Lice are some of the most persistent and undesirable pests in human history, and they have been discussed scientifically as far back as the 15th century. Unable to produce certain vitamins on their own, lice rely on a single food source — human blood — to provide the nutrition they need to survive.

Through the work of MSU AgBioResearch entomologist Barry Pittendrigh and his team of international collaborators, the marvels of modern genomic technology have brought newfound understanding of and new strategies to combat these miniscule irritants.

Two types of lice afflict human populations: head lice and body lice. Head lice, though nuisances that cause stress for parents, children and schools, do not present any medical risks to their hosts. In contrast, and despite their considerable genetic similarity to head lice, body lice serve as the vector for a number of bacterial diseases, including typhus and trench fever. Given the global prevalence and genetic similarity of both types of lice, discovering why one readily spreads disease and the other did not, became a focus for Pittendrigh. He, along with a world-spanning team of more than 60 researchers, received funding from the National Institutes of Health to map the louse genome and unlock the secret behind this disparity. It took five years to get the answer.

The completed louse genome revealed that head lice have a more robust immune system than body lice. This greatly restricts the variety of microorganisms that can survive within them and, therefore, migrate from them to new hosts. They also discovered that body lice in particular cannot produce vitamin B5 on their own, despite requiring it to survive and grow. These insights, Pittendrigh hopes, will allow researchers to develop new techniques for controlling not only lice but other pests as well.

“Since lice have such a small genome, this project allowed us to develop new insights into how insects become vectors of disease and the role of that in insect survival,” Pittendrigh said. “This will inform the development of pest control strategies for lice and other insects going forward.”