Residual degradation and toxicity of insecticides against Bactrocera oleae

Field and lab trials took place in Crete (July to September 2016), concerning the residual degradation and toxicity of seven active ingredients applied as bait sprays against the olive fruit fly. Highest residues were recorded in olive leaves for dimethoate and phosmet (~ 60 mg/kg) immediately after application (day 1+), while a threefold and fivefold reduction was observed 1 week later, respectively. Residues of pyrethroids were determined at lower levels (< 10 mg/kg) but remained almost stable for a longer period of time. Finally, thiacloprid and spinosad residues were determined at 5.81 and 0.19 mg/kg respectively (day 1+), and rapidly decreased below the LOQ. Highest toxicity against the olive fruit fly was observed just right after the application of dimethoate (100%), a-cypermethrin (80%), and L-cyhalothrin (72.92%). Although the toxicity of dimethoate was significantly reduced 1 week after the application (80%) and then minimized, toxicity of pyrethroids remained almost stable (> 60%) for the first 2 weeks and then decreased to 30-40%, which remained stable up to the end of the study (8 weeks). Concerning phosmet, its toxicity ranged from 35 to 56% for 3 weeks with no significant reduction, while spinosad presented a lower toxicity profile (50% only for 1 week). The benefits of these results in the knowledge of insecticide residues and their toxicity against olive fruit fly can be used for improving olive fruit fly control.