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Bees, Beetles, and Bacteria: the Cucurbit Bacterial Wilt Dilemma

Erika Saalau Rojas, Laura Jesse, and Mark L. Gleason

Department of Plant Pathology and Microbiology
Iowa State University
mgleason@iastate.edu

THE CASE: PART A

A second-generation farmer, Henry DeSoto, has decided to specialize in muskmelon production in a fast- developing suburban area. He farms approximately 40 acres, and is one of the few farmers left in the area. For the past 3 years, he has been selling muskmelon at local farmers markets. His profits are high, especially because he is very successful at harvesting his fruit early in the season, when prices are relatively high. His major production challenge is controlling cucumber beetles and the deadly disease that they carry: bacterial wilt.

Henry has experienced damaging bacterial wilt outbreaks. One year, he was too late in controlling the beetles and lost 80% of his crop. Ever since, he takes no chances and controls the beetles with a systemic neonicotinoid insecticide at planting and contact insecticide sprays throughout the season. Systemic neonicotinoid insecticides readily move inside plants and can be applied as seed, soil, or foliar treatments. Neonicotinoids are effective against a wide range of sucking and chewing insects and have a long residual activity. In contrast, contact insecticides are not translocated within the plant and insect pests are controlled by direct contact during or after spray applications. Contact insecticides are also effective against a wide range of insects but usually have a shorter residual effect when compared to systemic insecticides.

In addition to insecticide use, some farmers monitor the beetle populations in their fields and use scouting thresholds for cucumber beetles to decide whether they need to spray their crop or not; but beetle populations are hard to predict and scouting can be time-consuming. Henry feels he is too busy to scout and instead he prefers to spray insecticides at regular intervals. Henry’s insecticide-based approach means that he makes at least eight to ten insecticide applications per season.

One October evening, Henry receives a call from Deborah Kopper, a local commercial beekeeper who participates in the local community agriculture. Deborah has kept bee hives for 15 years and is chair of the beekeeping association in the county. There are 25 beekeepers across the county, and three of them are located within a mile of Henry’s farm.

Deborah mentions that there is a major concern among the beekeepers about the number of insecticide applications he uses on his crop. “Some beekeepers are noticing that their hives are not doing very well, and they’re blaming your excessive insecticide use for their problems.” Deborah says.

Henry has heard rumors about beekeepers pointing fingers at farmers for endangering bee health with the use of certain insecticides, but he decides to sound calm and confident. “Deborah, I’m using the latest vegetable pest control recommendations from the state university. All of my pesticides are labeled for cucurbit use, so I don’t need to apologize for anything I’m doing.” Henry replies.

“Well, Henry, I can’t stop you… yet. But I thought I’d give you a friendly warning before we file a legal complaint. The latest scientific research supports our claims. We now know that insecticides pose a risk to foraging bees, bee hive health, and other beneficial insects. Have a good day.”

A couple of days later, Henry received a letter stating that a lawsuit had been filed. The document stated that Henry’s management practices are detrimental to bee and colony health and that at least three beekeepers are suffering economic losses. Henry had hoped that Deborah’s call had been a bluff, but he now realizes that this issue will require his immediate attention. He already knew that using less pesticide could be a way to avoid complaints from neighbors, but he hadn’t seen the urgency of changing his ways until now.

Henry was upset. He thought, “I did nothing legally wrong! I don’t think there is conclusive research that points to insecticide use as being the main factor involved in poor bee hive health, but beekeepers are losing their livelihoods and insecticides have been implicated.” Henry thinks about hiring a lawyer but he knows that lawsuits are time-consuming and very expensive. Even if he wins this lawsuit, Henry will have to deal with all the bad publicity and being called a ‘bee killer’. This may cause his customers to question his use of pesticides and decide to stop buying his produce at the market.

A week later, Deborah calls again. She wants to help Henry, but his use of pesticides has put them both in a difficult situation. “If you are willing to consider using less insecticide”, Deborah says, “I’ll set up a mediation meeting with the beekeeping association. But if you decide to have this meeting, Henry,” Deborah warns him firmly, “we expect to hear a detailed management plan against cucurbit bacterial wilt that dramatically cuts your use of insecticides.”

What should Henry do?

QUESTIONS

  1. What is the role of cucumber beetles in this disease system? Does this role change your view of the disease triangle? Justify your answer.
  2. What are the signs and symptoms of cucurbit bacterial wilt?
  3. Describe the cucurbit bacterial wilt disease cycle.
  4. Can bacterial wilt be controlled by using fungicides or bactericides? Why?
  5. What do you think about Henry’s statement: “I did nothing legally wrong!”? Can the beekeeping association prove that he is responsible for poor health of the bees in their hives?

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