Repellency of volatiles from Martinique island guava varieties against Asian citrus psyllids.
The phytopathogenic bacteria Candidatus Liberibacter asiaticus (C Las) is the causal agent of huanglongbing (HLB), a destructive disease affecting citrus worldwide. It is vectored by the Asian citrus psyllid Diaphorina citri, an invasive pest that has spread across the Caribbean Islands and Florida over the last 20 years. It has been suggested that intercropping citrus and guava could significantly reduce populations of psyllids and consequently of HLB. Volatiles produced by some varieties of guava were analyzed and were found to be repellent to D. citri; unfortunately, intercropping trials conducted in Florida failed to efficiently reduce the population of D. citri and hence prevent HLB. We hypothesized that repellency against D. citri may depend on the variety and that some wild varieties may be more repellent than domesticated varieties. In Martinique Island, we tested the repellency of four different guava varieties, two commercially available, two found in the wild. Of the four, only one showed significant repellency against D. citri tested in Y-tube olfactometer assays. GC-MS assays revealed a higher concentration of dimethyl disulfide, a-selinene, and ß-selinene and a-copaene in the repellant variety. In separate olfactometer assays, a-copaene lures were shown to significantly repel D. citri. Our study may help to develop a better strategy using guava as an intercrop to improve the management of D. citri in Caribbean islands.