What is in this article?:
- New insect birth control strategy zaps cotton pests
- Refuge incompatible with eradication
- Combining pest-resistant cotton with the controlled release of sterile pink bollworm moths, a UA-led initiative has virtually rid Arizona of one the world’s most damaging cotton pests.
- Using pests as part of an insect birth control program helps to get rid of them, University of Arizona researchers have found.
The new approach that combines the planting of pest-resistant cotton and releasing large numbers of sterile moths has virtually eliminated some of the world's most destructive cotton pests from Arizona fields.
The novel control strategy, described in the Nov. 7 advance online publication of the journal Nature Biotechnology, has allowed growers to maintain high cotton yields without spraying insecticides to control pink bollworm.
"We are running the pesticide treadmill in reverse," said Bruce Tabashnik, department head of entomology in the UA's College of Agriculture and Life Sciences. "Our new approach has resulted in huge environmental gains. We are using cutting-edge technology to create sustainable cotton farming practices."
The new approach is part of a multi-pronged team effort to eradicate pink bollworm from the Southwestern U.S. and Mexico, in which Tabashnik and his co-authors play a leading role.
Caterpillars of the pink bollworm (Pectinophora gossypiella) are one of the most detrimental pests to cotton production worldwide. First detected in the U.S. in 1917, this invasive insect species wreaked havoc on Arizona's cotton-growing industry, with larvae infesting as many as every other cotton boll (the fruit capsule containing the precious threads).
A breakthrough came in 1996 with the introduction of Bt cotton, a genetically engineered crop containing a gene transferred from the bacterium, Bacillus thuringensis, endowing the plants with a protein that kills some, but not all insects. Unlike typical broad-spectrum insecticides, which kill most insects, pests or not, the Bt toxin only targets certain insect species. Pink bollworm caterpillars munching on Bt cotton die before becoming adults and therefore do not reproduce.
Bt crops have allowed farmers to cut back on spraying, but, much like antibiotics, have suffered from pests evolving resistance to the toxins, sometimes very rapidly. In fact, Tabashnik was the first to discover and document a case of a moth – not pink bollworm – evolving resistance to Bt toxins in crop fields.
"The most widely used strategy to delay resistance is to set aside refuges – patches with regular, non-Bt cotton where the pest can feed without ingesting the Bt toxin."
"If you plant Bt crops with no refuges, the vast majority of the caterpillars will die, but a tiny fraction will be resistant. These rare resistant survivors will emerge as adults and mate with each other."
The result is obvious: an exploding population of resistant insects.
The refuges ensure a substantial population of non-resistant insects will be around, fluttering about in search for mates. Given the abundance of non-resistant insects relative to the scarce resistant ones, chances are slim that two resistant moths will mate with each other. Instead, most, if not all, resistant moths will mate with a susceptible partner. When resistance is inherited as a recessive trait, the hybrid offspring produced by mating between resistant and susceptible moths are also susceptible.