Identification of the Sex Pheromone of the Spherical Mealybug Nipaecoccus viridis

Abstract

The spherical mealybug Nipaecoccus viridis is a pest of several major crops including soybeans, grapes and citrus varieties. Sessile virgin females of N. viridis release two volatiles, 2,2,3,4–tetramethyl–3–cyclopentene–1–methanol (γ–necrodol) and γ–necrodyl isobutyrate, on a circadian rhythm with peak at 17:00 (11 hr of photophase) as determined by automated, sequential solid phase micro extraction with gas chromatography−mass spectrometry analysis. The females increased the released amounts with age by about seven–fold from 5 to 6 d to 10–12 d of age. trans–3,4,5,5–Tetramethyl–2–cyclopentene–1–methanol (trans–α–necrodol) and trans–α–necrodyl acetate, found in essential oil of Spanish lavender, Lavandula luisieri, were rearranged to γ–necrodol and then used to synthesize γ–necrodyl isobutyrate. GC–MS and NMR data confirmed the identifications. In a petri dish bioassay, N. viridis males were significantly attracted to filter paper discs impregnated with γ–necrodyl isobutyrate but not to γ–necrodol or controls. A mixture of the two compounds was not more attractive than γ–necrodyl isobutyrate alone. Similar results were obtained with trapping flying adults, suggesting that the sex pheromone consists only of γ–necrodyl isobutyrate. This compound has not been reported previously in insects. Conversion of α–necrodol in lavender essential oil simplifies the synthesis of the sex pheromone and should allow its use in management of this cosmopolitan invasive pest.