It's been a great winter for the Texas Plains — unless you're a boll weevil. “We have lots of dead boll weevils,” says Jim Leser, Extension entomologist at the Texas A&M Research and Extension Center in Lubbock.
“We're a bit behind in checking overwinter sites because of rain, but with what we've found, plus findings from dig-up cages, we are extremely pleased,” Leser says, reporting on overwinter boll weevil survival rates for two counties: Dawson, which has completed one full year in the Boll Weevil Eradication Program, plus a fall diapause treatment; and Lubbock, which will begin a diapause program next fall. The analysis consists of eight sites in each county and three samples from each site.
“Last year, from the 24 samples we evaluated in Dawson County, we found five weevils and 80 percent were alive,” Leser says. “This year, we've found five weevils again and all are dead. All were found at one site, toward the western edge of the county, near Gaines County. We're not certain why that one site had weevils and the others did not.”
In Lubbock County, they found 287 weevils last year and 64 percent were alive. “This year, we've found only 18 weevils and all are dead,” Leser says. “We're not certain why and that baffles us. It is quite remarkable and tends to support what we're finding in dig-up cages.”
Leser says the winter has been wet, so scientists can not attribute the high weevil mortality rate to desiccation. Also perplexing is the high mortality in light of the way cold has hit the area.
Leser explains that for cold weather to kill weevils outright, temperatures need to get below 25 degrees. At that level, fluids freeze in the insect's cells, which rupture.
The coldest weather this year came with a cover of ice or snow that kept temperatures above the freezing point in habitat areas.
“High and low air temperatures in these areas would not differ more than one degree with snow or ice cover. That seems to be a fairly comfortable environment for boll weevils,” Leser say.
“We've seen some evidence, however, that mortality may result from chronic effects of several cold spells. We don't understand it yet, but it's the hypothesis we're working with.”
He says scientists are baffled not only by the high mortality rate of the weevils they've found but also the low number of weevils discovered in good overwinter habitat.
He says no evidence exists to indicate that warming temperatures in winter will tempt boll weevils out into the open where they may succumb to subsequent cold snaps. And they don't just disintegrate.
“Cold weather does not make weevils disappear, it kills them,” he says.
Dig-up cages in three locations, Seminole, Slaton and Plainview, reinforce the hypothesis that weevil numbers have been hammered by the winter cold snaps.
Technicians caught weevils last fall, brought them into a lab and fed them for three weeks to get them in superior condition to overwinter. They placed the weevils in traps, under good habitat conditions in the three locations and periodically dig the traps up to determine mortality.
Early mortality rates were disappointing, but since late January, survival has taken a significant downward trend.
Technicians checked Nov. 21 at all three sites and noted 100 percent survival. On Dec.15, 94 weevils still lived at Seminole (the southernmost site), 100 at Slaton (50 miles north), and 86 at Plainview (approximately 50 miles north of Slaton). By Jan. 5, numbers had dropped to 92 at Seminole, 78 at Slaton and 53 at Plainview. By Jan. 25, numbers had declined only slightly to 81 in Seminole, 50 at Slaton and 26 at Plainview.
“That still represented high survival rates,” Leser says. “I was disappointed.”
But the worm turned in February. On Feb. 14, only 67 weevils survived at Seminole; Slaton had 28 live ones and Plainview 16.
The last check, March 9, showed an even more precipitous drop: 31 at Seminole, 14 at Slaton and only four live weevils at Plainview.
“Our coldest weather occurred right around Christmas, so we did not see an immediate drop in survival,” Leser says. “It took them time to die.”
He compares the Slaton survival rate to previous years. “Ending survival counts include: 38 in 2000; 34 in 1999; and 57 in 1998. Match those figures, an average of about 45 live weevils per year, to the 14 left standing after the 2000-01 winter, and the spring looks promising.
“Anytime survival drops below 20 percent, we feel like we get some help,” Leser says. “If it drops below 10 percent, we feel like we've had a good winterkill. But 5 percent is what we want.
“Plainview has dropped below 5; and Slaton probably will by the next check. Seminole will not but likely will get closer to 20 percent.”
Leser says boll weevil mortality for 2000-01 will not be as dramatic as the winter of 1983-84, when only 1 percent survived. “It will be closer to the 1988-89 numbers, but that was and this looks to be an outstanding winter to help us with weevil control.”
He says benefits will accrue to farmers within active zones as well as those in zones that will start BWEP next fall.
“These high mortality rates will reduce the number of overwinter weevil applications required to control the pests early,” Leser says. “I expect a major positive impact.”
Leser says the low overwinter numbers also will help the Texas Boll Weevil Foundation through a year that's bound to be difficult. “They have a lot of new acres coming into the program and a lot of new personnel. If boll weevil numbers do not regenerate in the summer, fall populations will be lower and the foundation's job will be much easier.”
Leser says fewer overwintered weevil application sprays also may cause less disruption to beneficial insect populations and allow predators to take out more early-season and in-season pests.
“This year, because it's wet, does not look to be good for beet armyworm, either,” Leser says. “Farmers could be looking at a low pesticide use season.”
With the increased cost of energy and continued low cotton prices, farmers need anything that shows potential to improve the bottom line.
Leser also says potential to reduce overwintered and diapause treatments may ease pressure on malathion supplies, which could be tight due to manufacturing problems.
“Overall, I'm upbeat about the prospects for insect control for the High Plains cotton crop,” he says.
“In January I was disappointed. In mid-March, I was beginning to feel a little better. Now, I'm really smiling.”
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