Absolute Configuration of the Invasive Mealybug <i>Delottococcus aberiae</i> (De Lotto) Sex Pheromone: Synthesis and Bioassay of Both Enantiomers

The mealybug <i>Delottococcus aberiae</i> (De Lotto) (Hemiptera: Pseudococcidae) is an invasive pest reported in Europe at the end of the first decade of the 2000s, causing severe damage to citrus production in eastern Spain. In a previous work, (4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate was identified as the sex pheromone emitted by females, a new compound with an unusual β-necrodol skeleton possessing one stereocenter. This compound was assigned to the (-)-enantiomer but the absolute configuration was then not reported. In the present study, enantiomeric pure samples of both enantiomers were synthesized. X-ray diffraction analysis allowed the (-)-enantiomer, identical to the one emitted by virgin <i>D. aberiae</i> females, to be unequivocally identified as (-)-(<i>R</i>)-(4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate. Bioassays carried out to test the activity of both enantiomers under field conditions suggest that the presence of the (+)-(<i>S</i>)-enantiomer has detrimental effects on the activity of the racemates.