Detrimental effect of cypermethrin treated nets on Culicoides populations (Diptera; Ceratopogonidae) and non-targeted fauna in livestock farms

Bluetongue (BT) is an important disease of ruminants which exhibits its most severe clinical signs on cattle and especially on certain breeds of sheep. The known vectors of BT are small insects of the genus Culicoides (Diptera; Ceratopogonidae). Two species from this genus - Culicoides imicola and Culicoides obsoletus - play the major role in the transmission of the disease in Europe. Several prophylactic methods are used to avoid transmission; however, an easy and cost-effective preventive technique would be very useful for the control of the Culicoides populations near the animals. In the present study, the insecticide effect of cypermethrin treated nets on a Culicoides population was evaluated. A polyethylene net sprayed with 1L cypermethrin solution (1%) surrounding a UV light suction trap was placed at a cattle farm in Majorca (Balearic Islands). Collections of Culicoides and other fauna from the trap and floor around the net were compared with a control. Results showed no significant differences in the collection of Culicoides midges between the insecticide-treated net and the control. However, significant differences were observed in the collection of the non-target fauna between the treated net and the control, indicating that the dose used in the present trial was enough to kill most of the arthropods that contacted the net. The reasons for these equivocal findings and means to improve this technique for the control of Culicoides midges are discussed.