Further studies on the role of monoterpenes in pine host selection and oviposition of Thaumetopoea pityocampa

In a young mixed pine plantation (Pinus nigra and P. pinea) in central Italy, the influence of the pine needle monoterpenes (R)-(+)-limonene, (S)-(-)-limonene and (1S)-(-)-β-pinene on the oviposition activity of the pine processionary moth, Thaumetopoea pityocampa (Denis et Schiffermüller), was assessed. Two application methods were compared: spraying the trees with the substances emulsified with water, and setting up polyethylene dispensers from which the monoterpenes evaporated. During the moth's flight period weekly treatments (at 500 mg of monoterpene / l water) were carried out and the evaporation from the polyethylene dispensers (each with 5 g of a single monoterpene) was checked on each occasion by weighing the dispensers. The GLM analysis did not uncover any difference between the methods of application or between the pine species. T. pityocampa laid a significantly (P=0.01) lower number of egg masses on the trees treated with (1S)-(-)-β-pinene than on those treated with the other substances and on the control trees. A ∼45% reduction in egg mass number was obtained on the pines treated with (1S)-(-)-β-pinene, independent of the level of infestation, method of application or pine species. (R)-(+)-limonene and (S)-(-)-limonene were not effective.