The toxicological and residual properties of two insecticidal agents, Deltamethrin and Chlorpyrifos were evaluated against the German cockroach, Blatella germanica in laboratory bioassay. The insecticides were diluted in both aqueous and oil-based solvents and tested against the roaches in pre-determined concentrations and untreated control. Experimental cages were either completely sealed after exposure or perforated to simulate fumigation and disinfestation regimes, respectively. Mortality data generated from acute toxicity studies revealed that oil-based Deltamethrin (5%v/v) was more effective (100%) than aqueous solution (53.3%) within similar durations in both chambers. Chlorpyrifos (5%v/v) revealed an acute mortality of 100% for both oil-based and aqueous solutions in both chambers. Residual effect of both Deltamethrin and Chlorpyrifos was dose/time-dependent, with oil-based solution more effective than the aqueous solution. Computed lethal time revealed that LT50 showed significant difference (P<0.05) between aqueous solution of both insecticidal agents for fumigation treatment. A similar trend was observed for the oil-based solutions of both insecticides in the disinfestations treatment. The implication of this finding in terms of choice of insecticides for acute toxicity and residual efficacy, impact of diluting agents, and sustainable approach to roach control in Nigeria was discussed.
Key words: Blatella germanica, disinfestation, fumigation chambers.
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