155 Tropical Biomedicine 26(2): 155–164 (2009) Diminished reproductive fitness associated with the deltamethrin resistance in an Indian strain of dengue vector mosquito, Aedes aegypti L. Sarita Kumar, Anita Thomas, Thomas Samuel, Arunima Sahgal, Anita Verma and M.K.K. Pillai Acharya Narendra Dev College, University of Delhi, New Delhi 110 019. India Email: sarita.sanjay90@gmail.com Received 2 May 2009; received in revised form 15 May 2009; accepted 16 May 2009 Abstract. The susceptible (SS) and resistant (DLR) strains of Aedes aegypti selected with deltamethrin and combination of deltamethrin and PBO (1:5) at the larval/adult stage were studied in the laboratory for their reproductive fitness in terms of fecundity, hatchability and longevity of gonotrophic cycles. The DLR strains exhibited 73-88% reduction in the duration of gonotrophic cycles as compared to their SS counterparts. There was a considerable decrease in egg production and hatchability rates in the selected strains of Ae. aegypti, as compared to that of the SS strain. Data indicate deltamethrin being an effective insecticide against Ae. aegypti and a possible correlation between the deltamethrin resistance and disadvantages during reproduction. The most drastic and significant effect was observed in DLR1b strains exhibiting 36.7% decrease in fecundity and 32.4% reduction in hatchability. Another important observation was diminished reproductive fitness in DLR2 strains. This suggests the usefulness of synergized deltamethrin selections in reducing the frequency of resistant individuals. A significant finding was to observe the reproductive disadvantage in adult-selected strains having negligible resistance to deltamethrin implicating the efficacy of deltamethrin as an adulticide rather than as a larvicide. Various probable reasons for the reduction in the reproductive potential and the possible resistance-management strategies of Ae. aegypti are discussed. INTRODUCTION One of the most important vector borne diseases currently prevailing in most parts of the Tropics is dengue and the primary vector is Aedes aegypti L. In the Indian sub- continent, cases of dengue fever are on the rise and, therefore, the control of dengue vector needs immediate attention (WHO, 1999). The various measures for the control of this mosquito have been unable to control this, thus posing a serious threat to human beings. It has been observed that resistant and susceptible strains of insects frequently differ in fitness components, including longevity, fecundity and fertility, in addition to their susceptibility to insecticides (Arnaud et al., 2002). In general, resistant strains exhibit a reproductive disadvantage in the absence of insecticides (Roush & Plapp, 1982; Kono, 1987; Argentine et al., 1989; Li et al. , 2002), as a result of which, the frequency of resistant individuals may reduce over time (Roush & McKenzie, 1987; Arnaud & Haubruge, 2002). However, in certain cases, the resistant strains may have a fitness advantage and their frequency remains stable (Arnaud et al., 2002). A few researchers have reported that various insecticides reduce the fecundity of the treated Ae aegypti as compared to their susceptible counterparts. The adults of Ae. aegypti were found to lay few number of eggs after exposure to sublethal concentration doses of dieldrin (Duncan, 1963), d-phenothrin and d-allethrin (Liu et al., 1986) and abate (Reyes-Villanueva et al., 1990).