Biological Fitness of Spodoptera littoralis Adult Females from Emamectin Benzoate-Susceptible and -Resistant Cohorts

In this study, emamectin benzoate resistant strain was compared with susceptible strain based on the life table analysis.  Age specific survival rate (I_x) of adult females is mostly colony dependent and minimally temperature dependent.  This means that temperature regimes ranged from 15 to 35^oC are within the optimum zone for adult female surviving.  Gross reproductive rate (GRR) was the lowest at 30^oC that was 705.6 for susceptible colony compared to 565.8eggs/female from resistant colony. The net reproductive rate (R₀ or ∑ I_xM_x) for susceptible colony ranged from 470.36 at 15^oC to 303.41 female/female at 30^oC.  The corresponding values for resistant colony were from 287.85 at 15^oC to 113.16 at 30^oC.  The intrinsic rate of increase (r = R_m = R_max) for susceptible colony, was 0.0669 at 15^oC and increased gradually to reach 0.2861 at 35^oC.  Correspondingly, for resistant colony, the maximal intrinsic rate of natural increase elevated from 0.0538 to 0.2129 female offspring/mother female/day.  Similarly, the finite rate of population increase (λ) for susceptible colony elevated from 1.0692 to 1.331 female/female/day when temperature increased from 15 to 35^oC, respectively.  For resistant colony this parameter increased from 1.0553 to 1.2374.  Time required for duplicating the population of adult female was greater for resistant colony.  It was 1.24, 1.22, 1.37, 1.32 and 1.34-fold greater for resistant colony than that for susceptible colony at 15, 20, 25, 30 and 35, respectively.  In present study with emamectin benzoate selected colony, life table parameters (GRR, R₀, R_m, F_r), except Dt were less for resistant colony which refer to decrease the biological fitness with the evolution of resistance to this insecticide.