Abstract

Blattella germanica (German cockroach) is an urban insect pest in Nigeria due to an increase in strains that are resistant to the commonly used insecticides. The purpose of this study was to determine which of the insecticides used by pest control professionals are still effective. The insecticidal efficacies of dichlorvos (organophosphate-called sniper^©) and alpha cypermethrin (a pyrethroid called alpha action ^©) were determined in laboratory bioassays against B. germanica. Efficacy and response were affected by application rate of insecticide and exposure period. Insecticides mixed with diesel were more effective than those mixed with water. Insects exposed to the insecticides in closed chambers gave higher mortalities than insects in open chambers. B. germanica was more susceptible to dichlorvos than to alphacypermethrin in both open and closed chambers. Mortality of B. germanica increased with increase in concentration of the insecticide used. Sniper mixed in diesel was fastest acting insecticide against B. germanica where 100% mortality was observed 5 min post exposure in closed and opened chambers. Both insecticides gave 100% mortality of all insects exposed within 4 h of the exposure period. Sniper mixed with diesel had the LT₉₅ of 10 min while sniper mixed in water was 17 and 23 min, respectively in closed and opened chambers. The LT₉₅ of alphacypermethrin (5% (v/v)) mixed with diesel and water in closed chambers were 10 and 125 min, respectively. The residual effect of sniper and alphacypermethrin was less than one week.

Key words: Resistance, commercial insecticide, susceptibility.