Insecticidal Properties of Pyrethrin Formulations against Immature Stages of Phlebotomine Sand Flies (Diptera: Psychodidae)
Ireri, Laban Njeru
Tonui, W. K.
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Breeding sites of sand flies are complex; consequently using conventional larvicides to control larvae is not realistic and need improved strategies. A study was therefore conducted to evaluate susceptibility of immature stages of phlebotomus duboscqi Neveu Lemaire (Diptera: Psychodidae), to two phyrethrin formulations incorporated in larval food; an emulsifiable concentrate (0.5%) used as a mosquito larvicide and a dusting powder (0.2%) normally used against crawling insects. The concentrate was prepared into 0.2, 0.5 and 1 mg ml-1and each mixed with 1g of larval food, dried overnight and introduced into vials containing 10 larvae per instar. Similar concentrations of pyrethrin powder were prepared, mixed with 1g of larval food then kept overnight and introduced in similar vials as above. All the experiments were done in triplicate and mortality recorded daily. The larvae showed significant mortality (p<0.05) effects to the two formulations at 48h of exposure. Second and 3rd instars were more susceptible to Moskil than PylarvexTM with LD50 of 0.23 and 0.3 mg ml-1 for 2nd instars and 0.1 and 0.14 mg ml-1 for 3rd instars in 0.2 mg bioassays, respectively. However, there was no significant difference (p>0.05) in mortality between formulations and instars but significantly (p<0.05) differed between concentrations used. None of the larval stages managed to molt to the next stage, hence no pupal stages were observed. The results of this study demonstrate the clear entomological efficacy of pyrethrin formulations in larval food and should be considered for use in integrated leishmaniasis vector control programmes.