Rotenone:: Efficiency against olive fly (Bactrocera oleae Gmelin) and residual activity in olive oil

Rotenone solution (root extract of Derris elliptica; 10% or 20% a.i.) was tested as a bait with 2% hydrolysate protein in field trials to determine its efficiency against olive fly (Bactrocera oleae Gmelin). Olive trees cvs. Koroneiki and Tsounati located in the Nerokorou District of Chania, Crete were sprayed. Rotenone toxicity was tested against both adult and immature stages of olive fly in laboratory trials. A notable repellent action of the high concentration of rotenone solution was found while no selective activity of rotenone was observed between the two olive fly sexes. Duration of insect contact with the sprayed surface was crucial for the effectiveness of rotenone. Residues of both 10% and 20% rotenone solutions were monitored in olive oil extracted from fruit harvested immediately, and 4, 8 and 25 days after spraying. The rate of rotenone degradation was linear and fast in both treatments, depending on doses. Residue in olive oil was also monitored during storage in a tank in the dark at 20-26degreesC for 5 months followed by storage in transparent glass bottles in darkness or light at 20-26degreesC or darkness at -20degreesC for 3 more months. Monitoring of the residual activity in olive oil during storage (December 1996-August 1997) showed that light plays a dominant role in rotenone degradation. Rotenone residues were relatively stable in the dark at both temperatures. The rate of degradation after a period of 8 months was very slow (16%). However, olive oil samples stored for 5 months in the dark, followed by a three-month storage in the light showed a 44% decline in rotenone content.