Aerial spraying of Bacillus thuringiensis var. kurstaki for the control of Thaumetopoea processionea in Turkey oak woods

Thaumetopoea processionea L. is an important oak defoliator whose outbreaks have become increasingly frequent in Europe and thus have received a great deal of attention from foresters. Field trials were carried out in central Italy (Tuscany) to test the efficacy of aerial spraying of Bacillus thuringiensis var. kurstaki [Btk] in early spring for the control of processionary infestations in Quercus cerris L. woods. The experimental sites were located in a hilly area of 1640 ha with a maximum altitude of 593 m a.s.l. and a yearly mean temperature of 10 degrees C. Turkey oak woods were divided into three areas to be treated with 31.75 BIU ha(-1) (2.5 l ha(-1)) on 578 ha, 44.45 BIU ha-1 (3.5 l ha(-1)) on 306 ha and 57.15 BIU ha(-1) (4.5 l ha(-1)) on 756 ha, respectively. Five days after treatment, larval mortality was less than 40% in the control plot, but over 60% in the treated areas. Thirteen days after treatment, larval mortality varied from 75.05% to 96.42% in the three treated areas. Surveys conducted 2 months after the treatment showed a strong decline in the number of oak processionary nests in all the treated plots. It was possible to control the pest effectively in turkey oak woods using Btk at 31.75 BIU ha(-1) distributed at ultra-low volume at the time of bud opening when nonurticating larvae were present.