May 3, 2005

Stuck on you: Yellow traps catch cantaloupe beetles, study finds

WEST LAFAYETTE, Ind. – Cantaloupe growers who walk their fields searching for two crop-damaging insects can do just as good a job if they let the pests come to them.

A three-year study by Purdue University Extension entomologist Frankie Lam found that striped and spotted cucumber beetles captured with yellow sticky traps provided as accurate a pest count as traditional hand sampling. Lam's research also discovered that beetle activity is highest around midday.

The findings could lead to more timely and efficient insecticide applications for Hoosier cantaloupe growers.

Indiana ranks fifth among the states in cantaloupe production. Hoosier growers produced 50 million pounds of muskmelons in 2004 at a market value of nearly $10 million. Indiana's cantaloupe season runs from about late April to mid-July to meet peak demand around Independence Day.

The striped and spotted cucumber beetles, so named for the distinctive markings on their backs, are a danger to cantaloupe plants because the insects carry bacterial wilt disease. Once infected with wilt, cantaloupe plants die.

"Most growers sample cucumber beetles directly on the plants," Lam said. "It is difficult, time-consuming and labor-intensive."

Lam, who conducts research at Southwest-Purdue Agricultural Center near Vincennes, Ind., wondered whether yellow sticky traps might offer an alternative to hand sampling. The traps, which work along the same principle as flypaper, attract insects drawn to the bright yellow rectangles.

Lam placed traps randomly in research plots. Traps were positioned vertically just above the cantaloupe plants and horizontally at plant canopy level.

"I then counted the beetles every two hours from 8 a.m. to 4 p.m. on the following day after the traps were placed in the field," Lam said. "Each time I counted 10 plants on one replication. I sampled five times in a day and looked for the correlation between the beetles on the plants and the beetles on the traps.

"I found that if you have 20 beetles on a sticky trap within 48 hours, then you've reached the threshold of one beetle per plant on the muskmelon."

An average of one beetle per plant is a level sufficient for growers to consider applying insecticide, Lam said.

Lam's research also found that cucumber beetles are most active in the early afternoon. The insects apparently prefer warmer temperatures, he said.

"The beetles are most active at noon in the summer," Lam said. "For insects, different species may prefer different temperatures. I believe the cucumber beetle prefers a warmer temperature, but not a hot temperature. Early in the morning, the temperature may be too cold and the beetle may need to warm up before becoming active. Then after about 2 p.m., the temperature is hot and the insect is not so active. If growers want to sample for beetles, I recommend the best time to go out is roughly 11 a.m. to 3 p.m."

Sampling should be done two to three times per week in the first month of the growing season and once or twice per week after that until harvest, Lam said.

"The striped cucumber beetle has two generations during the crop season in Indiana but because harvest is tied to the Fourth of July, we're mainly concerned about the first population on cantaloupes," Lam said.

Sticky trap sampling should not add to cantaloupe growers' production costs, Lam said.

"The cost of direct sampling and using sticky traps may be similar," he said. "If you direct sample beetles, you'll have to hire people to count the insects. With sticky traps you don't need to do that. You only need to buy and set up the traps, wait for a few hours and then look at them and see how many insects you've got.

"Moneywise, it's more or less the same for both methods. But the sticky trap method may be easier than direct count."

More information on sticky trap sampling and cucumber beetle control is available in a pair of articles written by Lam for Purdue's Vegetable Crops Hotline newsletter. The newsletter is available online. "Using Sticky Traps to Sample Cucumber Beetles on Muskmelon" appeared in the newsletter's March 18 issue, while "An Integrated Pest Management Program for Cucumber Beetles on Muskmelons" appeared in the April 8 issue.

Ag Communications: (765) 494-2722; Beth Forbes, forbes@purdue.edu
Agriculture News Page

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: Frankie Lam, (812) 886-0198, wkflam@purdue.edu