Continued efforts to rid cotton fields in the West and Southwest of the pesky pink bollworm (PBW) insect,Pectinophora gossypiella, are moving the industry closer to eradication, but an issue with “suspect moths” has industry leaders tweaking the process.
The PBW is the most damaging, profit-stealing pest in Arizona cotton. Wherever the pest is found, female PBW moths lay eggs on bolls. The emerging larvae damage the boll by feeding on the seed; damaging the lint in the process. The damaged boll creates a potential pathway for other insects and fungi to enter.
State-based PBW eradication programs in California, Arizona, New Mexico, and West Texas, plus northern Mexico, are working in harmony toward the ultimate goal of eradication — zero native moths.
These efforts include increased planting of Bt (insect resistant) Upland cotton varieties, sterile moth technology, pheromone rope mating disruption placed throughout non-Bt cotton fields, and Delta insect traps for detection.
The sterile moth component is a major weapon in the war against the PBW. At the USDA-APHIS sterile moth breeding lab in Phoenix, Ariz., PBW moths are reared on a diet including red dye. The moths are irradiated to sterilize the insect’s reproductive system.
Sterile moths are transported to drop-off sites in California, Arizona, New Mexico, West Texas, and northern Mexico as part of bi-national eradication activities. Small aircraft drop an equal mix of male and female sterile moths over cotton fields daily.
Once they reach the ground, sterile and native (non-sterile) moths attempt to breed, but fail to reproduce since one insect is sterile. Delta sticky insect traps can capture a mixture of native and sterile PBW moths.
The sterile moth component is a proven success story in reducing native moth numbers across the western Cotton Belt. For example in Yuma County, Ariz., native moth trap captures have plunged from 61,000 moths in 2007 to zero moths last year.
This year, about 14.5 million sterile moths will be released daily over the cotton-growing areas through state-conducted eradication programs.
“The ultimate goal across the region is zero native moth captures,” said Leighton Liesner, director, Arizona Cotton Research and Protection Council (ACRPC), Phoenix, Ariz.
Liesner updated growers and pest control advisers on the PBW eradication program successes and the suspect moth issue during the 2012 Southwest Agricultural Summit in Yuma, Ariz.
In cotton fields, traps containing insects are gathered weekly and sent to identification labs in each state for analysis. The insects are placed under a microscope with 70 to 100 times magnification to determine whether PBW moths are present and whether the moths are natives or steriles, based on the presence or absence of red dye.
ACRPC leaders were surprised last year when traps at the lab for microscopic evaluation contained PBW moths apparently without red dye, the trademark of reared sterile PBWs. This suggested the insects could be background native populations.
At least one moth was found in each of the western Cotton Belt states (except New Mexico) and northern Mexico.
“Laboratory tests on live captured moths indicated the insects were sterile and could not reproduce,” Liesner said. “We do not believe it’s a background population. The suspect finds do not appear as a reproductive threat to the pink bollworm eradication program.”
So what is the culprit for the suspect moths? In short, no one knows. The culprit could be related to sterile moth technology or a host of other factors involving environmental issues including field temperatures, low or high moisture or humidity, or others.
Due to the suspect find issue, the National Cotton Council’s pink bollworm technical advisory committee has fine-tuned the sterile moth process. Other changes will enhance PBW control in the field.
The USDA rearing lab has increased by a total of 30 percent (in 10 percent increments) the amount of red dye fed to moths compared to the early days of the sterile moth program. In addition, advanced testing technology has been installed at the USDA Center for Plant Health Science and Technology lab in Phoenix to more accurately check captured moths for red dye.
USDA has also placed a second elemental marker in reared moths.
“The two marker system will provide higher diagnostic certainty to more precisely examine the moths,” Liesner said.
The ACRPC will apply additional pheromone rope in all non-Bt cotton fields in Arizona; thanks to a one-time cotton pest appropriation approved by USDA-APHIS. In Mexico, the areas of Mexicali, Baja California and San Luis, Sonora will do the same in a coordinated effort.
“There will be no out-of-pocket costs for cotton growers planting non-Bt cotton for the extra pheromone rope,” Liesner explained.
The concept of PBW eradication began in the late 1960s in California when the pest was first found in San Joaquin Valley cotton. The insect first established itself in Mexico in the early 1900s and proceeded through Texas, New Mexico, Arizona, and finally California to become a serious pest of cotton in the West and Southwest.
“If it wasn’t for the California Pest Control Board, we would not be where we are today in PBW eradication,” said Robert Staten, retired USDA-ARS entomologist, Phoenix, Ariz.
Staten has 42 years in sterile moth technology including his first job working on the PBW sterile moth effort in the Coachella Valley.
“Today, the Cotton Belt with the PBW is running similar to the SJV — growers are not treating with insecticides for pink bollworm since the native population is so low,” Staten said.
“In Arizona, we’re on the cusp of pink bollworm eradication,” he noted.
Credit for the evolution of sterile moth technology to fight native insect populations began with E.F. Knipling, who Staten calls “the father of sterile moth programs.” Knipling first applied the sterile moth process in the battle against screwworms.
For 40-plus years, California has utilized PBW steriles and other methods to reduce native moth numbers. Today, California follows a maintenance program to manage low native numbers.
In the entire U.S.-Mexico, PBW-affected cotton growing region last year, a single larva was found in an experimental Pima cotton field in Mexico. No larvae were found within the program areas in the U.S.
“With an organism like the pink bollworm, zero is a hard number to achieve,” Liesner said. “Sterile moths will remain our tool of choice.”
Reduced PBW counts have increased the opportunity for profitability in cotton production through the reduced use of insecticides.
Peter Ellsworth, University of Arizona IPM specialist, says IPM efforts against the PBW, lygus, and whitefly insects in cotton have heavily reduced insecticide use in the Grand Canyon State.
“At one time, Arizona cotton growers averaged nine sprays per season, but the number today is about 1.5 sprays for insects,” Ellsworth said.
Arizona cotton growers now pay the lowest insecticide control costs in history — more than $388 million saved cumulatively through 2011. In addition, nearly 19 million pounds less insecticide active ingredient enters the environment (or 1.7 million pounds annually).
Ellsworth said, “On average, 23 percent of Arizona cotton acreage is never sprayed for arthropods anymore. That’s something we never thought possible on a single acre 20 years ago.”