Surface contact toxicity and synergism of several insecticides against different stages of the tropical bed bug, Cimex hemipterus (Hemiptera: Cimicidae)

Abstract

Five formulated insecticides (lambda-cyhalothrin at 10 mg m⁻², bifenthrin at 50 mg m⁻², fipronil at 10 mg m⁻², fenitrothion at 50 mg m⁻², imidacloprid at 5 mg m⁻²) and one active ingredient (DDT at 500 mg m⁻²) were evaluated using a surface contact method against early and late instars and adults of two strains of the tropical bed bug, Cimex hemipterus (F.). Synergism of lambda-cyhalothrin and fipronil using piperonyl butoxide (PBO) was also assessed. The order of susceptibility of different stages of bed bugs was as follows: early stage-lambda-cyhalothrin > bifenthrin = imidacloprid > fipronil > fenitrothion > DDT; late stage-lambda-cyhalothrin > bifenthrin > fenitrothion > imidacloprid > fipronil > DDT; adult-lambda-cyhalothrin > imidacloprid > bifenthrin > fenitrothion > fipronil > DDT. The late instars exhibited significantly higher LT₅₀ among the life stages. The addition of PBO to fipronil increased the susceptibility of the insects. Lambda-cyhalothrin, bifenthrin, fenitrothion and fipronil at the recommended application rates were effective against C. hemipterus. Although imidacloprid demonstrated good initial response against C. hemipterus, the insects showed substantial recovery 72 h post-treatment. The late instars (fourth and fifth instars) should be used as the model for toxicological evaluation.