The pink bollworm is native to Asia but has become an invasive species in most of the world's cotton-growing regions. It reached the cotton belt in the southern United States by the 1920s. It is a major pest in the cotton fields of the southern California deserts.
The female moth lays eggs in a cotton boll, and when the larvae emerge from the eggs they inflict damage through feeding. They chew through the cotton lint to feed on the seeds. Since cotton is used for both fiber and seed oil, the damage is twofold. Their disruption of the protective tissue around the boll is a portal of entry for other insects and fungi.
Transgenic Bt cotton is resistant to the pink bollworm. Infestation on susceptible cotton is generally controlled with insecticides. Once a crop has been harvested, the field is plowed under as soon as possible to stop the life cycle of the new generation of bollworm. Unharvested bolls harbor the larvae, so these are destroyed. The plants are plowed into the earth and the fields are irrigated liberally to drown out remaining pests. Some farmers burn the stubble after harvest. Surviving bollworms will overwinter in the field and reinfest the following season. Populations of bollworms are also controlled with mating disrupting chemicals and releases of sterile males which mate with the females but fail to fertilize their eggs.