Insecticidal and residual effect of chlorfenapyr on different surfaces for the control of Sitophilusoryzae

Abstract

The immediate and residual insecticidal effects of chlorfenapyr applied on concrete and metal surfaces were evaluated against Sitophilus oryzae adults in laboratory bioassays. The dose used was 0.016 mg active ingredient (a.i.)/cm2 which refers to the highest label dose in case of severe infestation. Treated surfaces were either kept in continuous darkness or exposed to light. A series of subsequent bioassays were conducted in the treated surfaces, starting from the day of application and continued for three consecutive months, with new insects each time. For each bioassay, mortality levels were recorded after exposure for 3, 7 and 14 days. At the same time, the dissipation of chlorfenapyr residues on the treated surfaces was estimated at different time intervals (0, 3, 7, 15, 30, 60, 90 and 120 days) after application using a high-performance liquid chromatography system with a UV-detector (HPLC-UV). According to the results, mortality rates of S. oryzae adults after direct exposure to chlorfenapyr-treated concrete surfaces were high, reaching 100% at the end of the first bioassay. However, we observed a gradual reduction in mortality with the increase of the storage (post application) interval. On the contrary, mortality on metal surfaces was high and reached in all cases 100% after 7 days of exposure, regardless of the storage interval. Regarding the residues of chlorfenapyr on the surfaces, they remained relatively constant on metal surfaces for the entire 120-day period in both illuminated and non-illuminated surfaces. On concrete, an initial 20–35% reduction was observed over the first 3 days, whereas chlorfenapyr residues remained constant for the rest of the period regardless of the presence of illumination. Our results indicate that chlorfenapyr is effective for the control of S. oryzae, but its residual efficacy is moderated by the time after application, the surface type and partially by the presence of illumination.