Pink bollworm

Pink bollworm (Pectinophora gossypiella) is one of the most destructive pests of cotton in many areas of the world, including in India, China, Brazil and the western USA. In its adult, or moth, stage, the pink bollworm lays its eggs on cotton bolls. The eggs hatch into larvae that eat the cottonseeds and damage and discolour the fibre.

The National Cotton Council of the USA estimates that the pink bollworm costs American cotton producers more than $32 million each year in control and yield losses. In 2002 the US cotton industry started a programme to eradicate pink bollworm from cotton-producing areas of the US and adjacent areas of northern Mexico, which has advanced in phases upon passage of grower referenda. The eradication program embraces IPM; sterile insect releases are combined with mapping of cotton fields, monitoring of insect populations, insect-resistant cotton varieties, mating-disruption pheromones and cultural controls. The release of sterile moths is a critical part of the eradication program. More information is available on the NCC website. Once the pink bollworm eradication programme is successfully completed, there will still be a need for low levels of releases of sterile moths to prevent re-infestation.

An SIT program in California’s San Joaquin Valley has successfully prevented establishment of pink bollworm since 1970. Sterile moths are supplied from a mass-rearing facility in Phoenix, Arizona. Here insects are reared, irradiated as adults to sterilise them prior to release and marked with a red food dye. This facility now serves the entire eradication programme.

In a sterile moth release control programme, it is critical to be able to accurately determine whether moths caught in traps are released sterile ones or fertile wild ones. This is even more important in the later stages of an eradication program. Misidentification of a wild moth as sterile means an infestation may be missed. Misidentification of a sterile moth as wild means that resources will be wasted dealing with a non-existent infestation. In the current SIT program, released moths are marked with Calco Red dye administered in the feed, but there is a concern that this is not reliable enough now that the eradication program is well progressed. The industry is therefore interested in alternate markers that could be used instead of, or as well as, the existing food dye. Oxitec has developed a strain of pink bollworm that contains a heritable fluorescent marker which is otherwise identical to the strain used in the current SIT program and is sterilized by irradiation in exactly the same way.