Results and perspectives in the use of Bacillus thuringiensis Berl. var. kurstaki and other pathogens against Thaumetopoea pityocampa (Den. et Schiff.) in Italy (Lep., Thaumetopoeidae)

1998

S. 72-76

32 Lit. Ang.

Unselbständiges Werk

200104164

The pine processionary caterpillar, Thaumetopoea pityocampa is the most important defoliator of both native and introduced pines throughout Italy and is especially damaging in young plantations and on ornamental trees. A number of microbial pathogens have been isolated from larvae and pupae over the last 30 years. Some of them have been evaluated as biological control agents, and have provided encouraging results. However, only Bacillus thuringinensis var. kurstaki (Btk) has passed the experimental screening and is now available for routine treatments, although its application by air is subjected to strict regulation by the government. The erratic performance of a single application of Btk against Thaumetopoea pityocampa that has been observed in the field (20-85% mortality) is related to a great variability in both the application dose and some population parameters of Thaumetopoea pityoeampa. The emergence period of adults varies from July (Alps) to October (South) and its duration is related to the spreading of the cohorts (individuals with different length of prolonged diapause) over time. In addition, embryonic development takes from 20 to 45 days, depending strictly on the temperatures recorded in the egg masses. As a result, the most vulnerable larval instars (L1 and L2) are never thoroughly reached by one application only, as the persistence of the bacteria on the needles is usually limited. Two applications are requested to control the pest in stands where the egg hatching occurs over more than one month. Another possibility consists of a single winter application against L3-L4 with a higher dose, to be performed where a certain amount of damage is tolerated.