Assessment Of Insecticide Resistance Risk To Commercial Gel Bait In Field Pyrethroid-Resistant German Cockroaches

In the present study, we tested three field populations of German cockroaches, which are characteristic of being susceptible to deltamethrin but resistant to fipronil (WF), low resistance to deltamethrin and fipronil (CR), and high resistance to deltamethrin and fipronil (BZ). The test cockroaches were subjected to fipronil-, imidacloprid- and indoxacarb-containing commercial gel baits. The surviving cockroaches were reared for the next generations. The lethal dose causing 50% population mortality was generated. The values of LD₅₀ from each population under respective treatments were compared with laboratory susceptible strain (EHI) to generate a resistance ratio (RR₅₀). The result showed that the RR₅₀ for fipronil in WF and BZ remained high throughout generations, with RR₅₀ ranging from 8.9 to 25.8. Increasing RR₅₀ (1.4 – 5.0) was also observed in CR. In contrast, a subtle or gradual increment in RR₅₀ was observed under imidacloprid and indoxacarb gel bait treatment in test populations irrespective of resistance status. In conclusion, the resistant status is essential in determining the performance of fipronil-containing bait.