Review and analysis of damage functions and monitoring systems for pink bollworm (Lepidoptera: Gelechiidae) in southwestern United States cotton

Pink bollworm, Pectinophora gossypiella (Saunders), continues to be a significant pest of cotton worldwide. Two factors essential for effective integrated pest management (IPM) programs for pink bollworm include: 1) quantification of damage-yield relationships, and economic injury levels, and 2) practical sampling plans for estimating pest density, or classifying the pest population above or below an economic threshold. Research conducted over the past 30 years is reviewed in an effort to quantify damage functions, and to assess the advantages and disadvantages of several common monitoring methods for pink bollworm. Composite results of five independent studies from 1969 to 1991 show that yields are not reduced until the average seasonal larval infestation in bolls approaches 15%. Each study shows that insecticide applications are significantly reduced when economic thresholds (ETs, based on moth catches in pheromone traps, or egg or larval infestations in bolls) are used. Compared with scheduled applications, the average reduction in insecticide use, based on ETs, ranged from 23 to 37% with no reduction in yield. Although monitoring adult moth flights with pheromone traps continues to be a popular tool, the recent development of binomial (presence-absence) sequential sampling plans for pink bollworm eggs offers several advantages, including an indirect indicator of female moth activity and earlier detection of subsequent larval infestations in bolls. Recent commercialization of Bt-cotton, genetically transformed to express an insecticidal toxin from the bacterium, Bacillus thuringiensis, provides considerable promise for consistent control of pink bollworm. However, its continued use will depend upon rapid development and adoption of resistance management plans by growers. Moreover, the use of Bt-cotton is likely to be preserved longer if it is implemented within the context of an integrated pest management (IPM) program, rather than as a single tactic.