INFLUENZA DI MONOTERPENI SULLE FEMMINE OVIDEPONENTI DELLA PROCESSIONARIA DEL PINO.

The preference shown by females of the pine processionary moth, Thaumetopoea pityocampa (Denis & Schiffermüller) for oviposition on certain species of pine may be influenced by semiochemicals released by the trees, in quantities differing according to the species and the period of the year. During investigations focused on identification of volatile metabolites present in needles of 5 pine species (Pinus nigra, P. pinaster, P.radiata, P. sylvestris and P. pinea) limonene concentration resulted higher in P. pinea, the least sought by the pine processionary moth than in other pines, particularly during the summer period, in concomitance with flights of the moths. Trials were carried out in 1999 in three young pure pine stands, composed respectively of P. nigra, P. pinaster and P.radiata, by spraying the trees with (R)-(+) and (S)-(-)-limonene and with (1S)-(-)--pinene and (1S)-(-)--pinene, other terpenes found in the needles. The trials were repeated in 2000 in a purpose-established pine plantation with specimens of the first two above-mentioned pine species and P. pinea. In all trial years, pines treated with limonene, and particularly those treated with the enantiomere (R)-(+), showed a significantly lower number of eggs compared to untreated pines. -pinene was shown to have an even more pronounced disorientating effect on females than limonene, above all in the year 2000. In contrast, -pinene exerted no activity. These results are of considerable interest as they suggest the concrete possibility of achieving protection of pine forests against the pine processionary moth by using terpenic compounds to disorientate females during the host location for oviposition.