Are Australian field‐collected strains of Cimex lectularius and Cimex hemipterus (Hemiptera: Cimicidae) resistant to deltamethrin and imidacloprid as revealed by topical assay?

Resistance profiling on Cimex lectularius and Cimex hemipterus in Australia has previously revealed the existence of resistance to pyrethroid insecticides and that multiple resistant mechanisms exist in field populations. To further investigate insecticide resistance in modern field populations of bed bugs, a program to collect and screen field specimens was initiated. Over 50 bed bug strains (a mixture that included both C. lectularius and C. hemipterus) have been collected from across Australian, with 35 subsequently colonised (31 C. lectularius and 4 C. hemipterus) for laboratory-based insecticide resistance testing. Bed bugs were exposed topically to pyrethroids at a discriminating dose of 2.5 g/L deltamethrin in acetone applied at a rate of 1 mu L/bug and, for neonicotinoids, a dose of 0.1 g/L of imidacloprid applied at a rate of 1 mu L/bug. Mortality was recorded 24 h post application. Twenty adult bed bugs of mixed sex and age in two replicates of 10 were used for the bioassays, plus controls. Results indicated a broad spread in the frequency of resistance against deltamethrin in C. lectularius, represented by a range of mortality values between 15 and 100%. Mortality was predominantly uniform with C. lectularius against imidacloprid at >= 95%, except for several recently collected strains that returned between 70 and 85%, indicating that a degree of tolerance may be developing in select strains. Three of four C. hemipterus strains returned mortality values at or below 10%, with the remainder recording 75% mortality, thereby indicating pyrethroid resistance is similarly advanced in this species. Normal susceptibility (>= 95% mortality) was otherwise evident in all four C. hemipterus strains to imidacloprid. These findings complement concurrent research, which indicates that variable patterns of resistance are present across the country and around the world. The results have profound implications for product manufacturers and registration authorities in ensuring that a product is as effective at controlling bed bugs in the field as the laboratory.