Inefficient weapon—the role of plant secondary metabolites in cotton defence against the boll weevil

Plant cultivar selection for resistance to herbivore pests is an effective, environmentally safe and inexpensive method to implement in integrated pest management programs. In this study, we evaluated seven cotton genotypes with respect to the production of volatile organic compounds (VOCs) and non-volatile compounds (terpenoid aldehydes (TAs)), and the attraction and feeding preference of adult boll weevils. Chemical analyses of VOCs from BRS-293, BRS-Rubi, CNPA TB-15, CNPA TB-85, CNPA TB-90, Delta Opal, and Empire Glandless showed that there were few qualitative and quantitative differences across the range of genotypes. In contrast, major differences in TA content were observed, with CNPA TB-15 and CNPA TB-85 producing higher levels of TAs compared to the other genotypes. Our results showed that boll weevil attraction and feeding behaviour was not positively or negatively influenced by the terpenoid content (volatile and non-volatile compounds) of cotton genotypes. The results in this study suggest that boll weevils have adapted physiologically to cope with cotton chemical defence mechanisms.