Objective:To evaluate the effects of deltamethrin against field-collected adults of Aedes aegypti L(Ae.aegypti).Methods:The adults were selected with 0.025%deltamethrin for 40 successive generations.The selected adults were tested with 4%DDT and the emerging larvae were tested with various insecticides to study the cross-resistance spectrum.The knockdown and irritability studies were carried out in adult mosquitoes to investigate their behavioural response to deltamethrin.Results:Forty generations of selection with deltamethrin resulted in only 3.8-fold resistance in the adults of Ae.aegypti.The adults of parent(PS) and selected strains (DAS) exhibited only 0.8-fold cross resistance to 4%DDT.The larvae emerging from the PS and DAS strains did not develop appreciable levels of resistance to various insecticides tested.The knockdown studies revealed KTSO of 14.4 min in PS adults with no signs of recovery even after 24 h. The DAS strains could develop only 1.2 to 1.3-fold knockdown resistance(KDR).The knockdown response of DDT was though 5-6 times slower than deltamethrin but the continued response in deltamethrin-selected adults caused only 1.2-fold KDR.The PS and DAS strains exhibited significant irritability response towards deltamethrin and DDT.The DAS strains showed 5-6 fold increased irritability to deltamethrin as compared to the PS strain.Conclusions:The above results suggest the prolonged effective use of deltamethrin against Ae.aegypti as an adulticide. Objective: To evaluate the effects of deltamethrin against field-collected adults of Aedes aegypti L (Ae. Aegypti). Methods: The adults were selected with 0.025% deltamethrin for 40 generations generations. The selected adults were tested with 4% DDT and the emerging larvae were tested with various insecticides to study the cross-resistance spectrum. The knockdown and irritability studies were carried out in adult mosquitoes to investigate their behavioural response to deltamethrin. Results: Forty generations of selection with deltamethrin resulted in only 3.8-fold resistance in the adults of Ae. aegypti. The adults of parent (PS) and selected (DAS) included only 0.8-fold cross resistance to 4% DDT. The larvae emerging from the PS and DAS strains did not develop appreciable levels of resistance to various insecticides tested. The knockdown studies revealed KTSO of 14.4 min in PS adults with no signs of recovery even after 24 h. The DAS strains could develop only 1.2 to 1.3-fold knockdown resist ance (KDR). The knockdown response of DDT was though 5-6 times slower than deltamethrin but the continued response in deltamethrin-selected adults caused only 1.2-fold KDR.The PS and DAS strains exhibited significant irritability response towards deltamethrin and DDT. DAS showed 5-6 fold increased irritability to deltamethrin as compared to the PS strain. Conclusions: The above results suggest the prolonged effective use of deltamethrin against Ae. Aegypti as an adulticide.