Effect of the combined application of microencapsulated synthetic oviposition pheromone (MSP) with different larvicidal agents on the oviposition of Culex pipiens biotype molestus.

BACKGROUND: Attract-and-kill strategies, in which a behavior-modifying stimulus (e.g. a pheromone) is integrated with a pest control agent, have lately attracted increased interest for mosquito control. Previously, it was demonstrated that the polyurea microencapsulated synthetic oviposition pheromone 6-acetoxy-5-hexadecanolide (MSP) was sufficiently attractive to gravid females of Culex pipiens L. biotype molestus Førskal (Diptera: Culicidae) for a period of 40 days. Furthermore, it was shown that MSP could be effectively combined with the organophosphate temephos to achieve efficient mosquito control. In the present study, the effect of the combined application of MSP with commonly used larvicides on the oviposition response of Cx. p. biotype molestus females over time was investigated in two-choice oviposition bioassays. As larvicides, the insect growth regulator diflubenzuron and the bacterial insecticide spinosad were evaluated at their lowest recommended label dose, whereas temephos was used as a control.

RESULTS: When MSP was applied in combination with diflubenzuron, the attractancy of MSP to gravid females was in all cases negatively affected, as fewer egg rafts were laid in pots treated with MSP and diflubenzuron compared with MSP alone. Spinosad did not reduce, but rather increased, the attractive effect of the oviposition pheromone at the beginning of the bioassay (at 2 days of ageing) when co-applied; however, the observed attractive effect was significantly reduced after 7 days of ageing and remained stable at the same level until the termination of the bioassay. Finally, the oviposition pattern of egg rafts laid on the pot with MSP and temephos was similar to that of egg rafts laid on the pot with MSP alone, showing that temephos did not significantly affect MSP activity.

CONCLUSION: The results of the present study highlight the effects of the combined application of MSP with spinosad and diflubenzuron on the oviposition of gravid Cx. p. biotype molestus females, which in most cases eliminated the attractive effect of MSP. © 2017 Society of Chemical Industry.