Pyrethroid resistance in the cigarette beetle Lasioderma serricorne (F.) (Coleoptera: Anobiidae)
Spraying application of contact insecticides onto building surfaces (walls and floors) is a key measure to control the cigarette beetle Lasioderma serricorne (F.) population in tobacco warehouses. Pyrethroids have been used widely as effective surface-spray agents since the 1970s. Recently however, resistance to deltamethrin (a popular pyrethroid) was found in a L. serricorne population collected in Germany. This study was conducted to ascertain if the pyrethroid resistance has spread among field populations of L. serricorne. Specifically, we examined the efficacy of two pyrethroids (permethrin and bifenthrin) for seven strains that were collected originally from tobacco warehouses at different locations. The treatment was applied by dipping adults for 10 s in the insecticide solution. Their viability was assessed 48 h after the treatment. Then LC99 was determined. Results show that both insecticides exhibited high efficacy against four of seven strains at practical dose levels (235-384 ppm in LC99 for permethrin and ≤25 ppm in LC99 for bifenthrin). By contrast, high resistance was observed in the other three strains: most insects survived exposure even at an over-label dose (10,000 ppm). These results suggest that pyrethroids lose their effectiveness against many L. serricorne field populations through resistance development. Therefore, pyrethroids cannot be recommended today as insecticides of primary choice for L. serricorne.
Considering the development of pyrethroid resistance, we evaluated three insecticides as potential alternatives (fenitrothion, pirimiphos-methyl, and spinosad) with respectively different modes of action from that of pyrethroids. The efficacy of insecticides to pyrethroid-susceptible and pyrethroid-resistant strains was assessed in the manner described above. Susceptibility of pyrethroid-susceptible and pyrethroid-resistant strains to those insecticides was not significantly different (within 2.3-fold resistance ratio). The results indicate that insecticides such as organophosphates (fenitrothion and pirimiphos-methyl) and spinosad have potential for use as surface-spray agent alternatives to pyrethroids.