Pheromone Chemistry of the Citrus Borer, Diploschema rotundicolle (Coleoptera: Cerambycidae).

The citrus borer, Diploschema rotundicolle, is a Neotropical longhorn beetle that has become a serious citrus pest in southern South America. Management strategies for this insect rely on trimming off damaged shoots, which is expensive and inefficient. We studied the chemical communication system in D. rotundicolle in search of attractants for monitoring or control. GC-MS and enantioselective GC analyses of volatile extracts from field-collected adults showed that males produce (R)-3-hydroxy-2-hexanone, irregularly accompanied by minor amounts of 2,3-hexanediol (all four stereoisomers) and 2,3-hexanedione. Males emit the compounds only at night, when the adults are active. GC-EAD analyses of natural and synthetic compounds showed that both male and female antennae respond to the natural enantiomer (R)-3-hydroxy-2-hexanone, suggesting that it may function as an aggregation-sex pheromone as seen in many cerambycines. The non-natural (S) enantiomer as well as the minor component 2,3-hexanediol did not trigger antennal responses. Field tests with the racemic 3-hydroxy-2-hexanone, enantiomerically pure (R)-3-hydroxy-2-hexanone, as well as a mixture of racemic 3-hydroxy-2-hexanone and 2,3-hexanediol, showed in all cases low capture levels of D. rotundicolle. However, increasing the elevation of the trap and the emission rate of dispensers enhanced field captures in traps baited with racemic hydroxyketone. Incidental catches of another native cerambycine, Retrachydes thoracicus, in traps baited with 3-hydroxy-2-hexanone are also reported. This is the first report of pheromone chemistry in the genus Diploschema and in the tribe Torneutini, reaffirming the pheromone parsimony well established for the Cerambycinae. Potential factors explaining the weak attraction of D. rotundicolle in the field are discussed.