Suitable alternatives to organophosphates are available for Western cherry fruit fly, says a U.S. Department of Agriculture scientist. But achieving complete control with the new chemistries is difficult.
Western cherry fruit fly (Rhagoletis indifferens) is a quarantine pest for many sweet cherry growers. Certain markets, like California, have a zero tolerance for the pest in cherries shipped there. Though the pest is traditionally controlled with organophosphate and carbamate pesticides and preventative sprays, the industry is looking for reduced-risk alternatives.
Dr. Wee Yee, entomologist at USDA’s Agricultural Research Service laboratory near Wapato, Washington, is testing bait sprays that will attract and kill the flies, as well as insecticides to control the fly. He shared results of his research during the annual Cherry Institute meeting in Yakima, Washington.
Bait sprays have been routinely used to manage the Mediterranean fruit fly, according to Yee. The same concept of attracting flies to the bait and then killing them is being tested in Washington State cherry orchards.
An effective bait spray could have potential use in border rows to prevent flies from migrating into the orchard.
Yee tested three combinations of baits with spinosad (GF-120, Nulure, and Mazoferm) to measure the degree of attractiveness of the baits. Nulure and Mazoferm have been used as baits for other subtropical fruit flies. In both far-range and close-range tests, he found that the baits were not very attractive and did not lure flies to the baits.
In feeding trials, he found that cherry fruit flies fed longer on the GF-120 formulation than on the other two baits. GF-120 is composed of molasses, yeasts, and other compounds, plus spinosad (an insect growth regulator sold as Success and the organic formulation Entrust).
The duration of feeding is important, he said, because the longer the fly feeds on the bait, the more toxins it ingests. He also evaluated the effectiveness of the bait sprays in controlling flies.
“There was no clear relationship between attraction and control,” Yee said, adding that the baits and spinosad were similar in effect. “None of the baits were very attractive at the close or far range. The flies were just as likely to feed on water as the baits.”
He also noted that none of the baits were significantly different in control as long as there was spinosad in them.
Yee also compared different reduced-risk insecticides for efficacy. He tested the spinosad/bait product of GF-120, spinosad by itself (Entrust), and two chloronicotinyls Provado (imidacloprid) and Calypso (thiacloprid).
Laboratory tests showed that Entrust had high toxicity to cherry fruit fly for up to three days, but Provado, Calypso, and GF-120 also were effective.
When leaves were sprayed in the field, Entrust and GF-120 were more effective than Provado and Calypso on the application day. But on the third day, GF-120 began to outperform Entrust, he said.
“Even at 14 days, GF-120 was still effective in controlling the fly,” Yee said. “Under field conditions, GF-120 has some property in it that reduces the loss or breakdown of the chemical.”
When eggs were exposed to the materials, Calypso was the best initially at killing eggs, but all materials killed the eggs with constant exposure, he added.
Tests on single, infested trees showed that all materials were effective, though he noted that the trial had low fly densities. Other research has shown Calypso to be the least effective in reducing infestations, but Yee has been unable to confirm that.
He concluded that Entrust, GF-120, and Provado seem to be suitable substitutes for organophosphate insecticides in managing cherry fruit fly.
“But they need to be applied every seven days after the first fly catch,” he stressed. “Until more data comes in, I would be hesitant to recommend spray intervals longer than seven days.”
While data show that there are alternatives to broad-spectrum chemicals like Sevin, Guthion, malathion, and dimethoate, there are no silver bullets in eliminating the quarantine pest.
“The problem is that we are unable to achieve 100 percent control,” Yee said. This might be related to the lack of attractiveness of the baits, but it is clear that more research is needed, he said.
“We also need insecticides that protect the fruit from gravid flies that are full of eggs and come in from surrounding infested trees. Within-orchard control is much easier than controlling flies coming in from the outside.”