Knowing Your Roots

Blog 13

Anyone who has tried to grow their own tasty potatoes has probably run into the ravages of the dreaded ‘potato bug,’ which often devours your potato vines before your tubers even had a chance! This black and yellow striped adult beetle (and its brick red, hump-backed young) is actually the Colorado potato beetle. It originated in Mexico and was innocuously living on buffalo burr plant in the arid prairies of the Western United States when early settlers introduced a new miracle food to the area—the cultivated potato. These beetles just loved this new nutritious food that settlers were now planting for them, and they adapted fast and began multiplying at astonishing rates, spreading eastward and devouring potatoes wherever they found them.  They even managed to cross the Atlantic and became the scourge of potato growers across Europe and Asia! This potato-eating machine quickly became the number one insect potato pest worldwide.

There are many reasons that account for the beetle’s continuing success and longevity as a pest, including their perfect synchrony with the potato ecosystem and the lack of natural enemies to keep them in check.  Their greatest achievement, however, has been their uncanny ability to develop immunity to every kind of insecticide that has been used to control them.  This ability dates back to the very early days; they were the first insect pests to be subjected to widespread and systematic applications of synthetic insecticides—nothing else could prevent total crop loss. This approach worked initially, but success was fleeting as the beetles quickly developed ways to biologically overcome the effectiveness of these crude sprays—just the beginning for the master of adaptability. Since then, the beetle has been able to resist more than 50 different insecticides representing virtually every mode of action that scientists have been able to devise, rendering some ineffective in as little as a year or two!  At times, it became so difficult to find an insecticide that still worked that potato growers commonly resorted to burning them off plants with propane and then vacuuming them from plants with huge motorized ‘bug-vacs!’  

Things began to change in the 80s when scientists developed cultural control strategies that exploited weaknesses in the beetle’s life cycle, and the U.S. Environmental Protection Agency began to actively encourage the registration of insecticides that posed reduced risk to both humans and the environment.  Anders Huseth, a graduate student with Professor Russ Groves at the University Of Wisconsin – Entomology Department (now at North Carolina State University) calculated that from 1970 to 2010, the environmental impact of insecticides registered for use against potato beetles decreased by over 90%!  The biggest impact came from a group of nicotine-like insecticides (the neonicotinoids or ‘neonics’ for short) that entered the marketplace in the mid-90s.  These materials were extremely effective at very low doses, safe for humans and the environment, and as a result, their popularity spread quickly among growers; they have been used on virtually all potato acres across the U.S. for the past two decades.

Neonics are still widely used today, but the beetles are once again showing their mastery of adaptability by developing resistance.  Resistance is Huseth’s specialty; he has calculated that the duration of effective control that growers get from when the neonics are applied at planting until they no longer work.  It has declined by over 50% since 1995—a whopping 50 days that growers now have to fill with other insecticides, eating into profit margins and increasing the risk of beetles being able to develop resistance to new materials.

Huseth and fellow UW researchers are now using advanced satellite-based, remote sensing technology to document the frequency of potato fields in the landscape and adding this information to the insecticides growers are using and the beetle’s genetic pre-disposition to estimate how quickly resistance will develop over time. They are using this information to design long-term plans that growers can use for managing resistance. These plans employ a combination of cultural control tactics to reduce beetle populations and switching between reduced-risk insecticides with different modes of action. The strategies now used to manage resistance to the Colorado potato beetle are prolonging the effective lives of new low risk insecticides, enhancing the environment and benefiting both growers and consumers.  Another good example of the far reaching impacts that research at the UW is having on how our potatoes are grown!

For more information contact Dr. Anders Huseth (ashuseth@ncsu.edu) and Professor Russ Groves (http://labs.russell.wisc.edu/vegento/)

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