The Aggregation Pheromone of Metamasius spinolae (Coleoptera: Dryophthoridae) Revisited: Less is More

The weevil Metamasius spinolae (Gyllenhal) is the most important insect pest of cultivated prickly pear in Mexico. A previous work reported that the pheromone of this weevil species was composed by three components. In this study, we reinvestigated the aggregation pheromone of M. spinolae using gas chromatography-electroantennography and gas chromatography-mass spectrometry to locate and identify new potential pheromonal compounds. The behavioral activity of identified compounds was evaluated in laboratory and field trials. Metamasius spinolae males released four compounds: 2-methyl-4-heptanone, 6-methyl-2-hepten-4-one, 2-methyl-4-octanone, and 2-hydroxy-2-methyl-4-heptanone. In the laboratory assays, depending on the concentration, the compounds were attractive, neutral, or repellent to M. spinolae. Field evaluation showed that traps baited with 2-hydroxy-2-methyl-4-heptanone singly or in most of the binary or tertiary blends where this compound was present captured a higher number of M. spinolae compared to live males and the other compounds identified. In conclusion, our results indicate that 2-hydroxy-2-methyl-4-heptanone is the main component of the aggregation pheromone of M. spinolae. We suggest that this compound should be used for developing a monitoring or a mass-trapping system for M. spinolae.