Reproductive performance of cotton leaf worm spodoptera littoralis exposed to necotinoids

Neonicotinoid insecticides, is the nicotinic acetylcholine receptors agonist, have been widely used against several insect pests. Insect individuals exposed to an insecticide, exhibit differences in susceptibility and responses to insecticide stress like Spodoptera littoralis (Boisd) (Lepidoptera: noctuidae) one of a distinct attacking crop pests in Egypt. Lifetable assessment after exposure become urgent need to evaluate newer insecticide efficacy. Laboratory rearing ad field batch from S. littoralis were exposed to sublethal dose for acetamiprid, thiamethoxam and imidacloprid for monitoring life table under this stress. Results reveals values of LC50 refers to imidacloprid was the most effective and acetamiprid was the less effective for both susceptible and field population. Survival rate of the developmental stages larvae pupae and adult was lower in susceptible than in field for the three insecticide, and control were more than 97%. The number of individual expected to live the same age but different stage is the Life expectancy (ex) of 4th instar larvae were ranged between (11.45, 5.2, 7.3 and 6.0) and (6.4, 3.5, 3.6, 3.0) for thiamethoxam, imidacloprid, acetamiprid and control, of susceptible and field population, respectively. The mean of reproductive rate (R0) of the susceptible ranged from (1.35 to 1.88) and (4.79) for control but field population R0 ranged from 1.19 to 1.52 and 3.77 for control. The mean generation time (T) for susceptible was 24.98, 24.12, 30.05 and 24.19 days for control, acetamiprid, thiamethoxam and imidacloprid respectively and field was 24.88, 23.31, 59.9 and 23.9 days for field respectively. The average intrinsic rate of increase (rm) allows the intrinsic birth, death rate, and the stable age distribution determination, and describe the population dynamics, and for susceptible was 0.063, 0.012, 0.016, and 0.026 and for field was 0.053, 0.007, 0.016, and 0.018 female per female per day. The finite rate of increase (λ) is the number of individuals in each age-stage group will increase λ-fold after one age was 1.056, 1.013, 1.017 and 1.026 for susceptible and 1.55, 1.07, 1.012, and 1.018 for field of acetamiprid, thiamethoxam and imidacloprid respectively. Results showed elongation in developmental period of treatments compared with control and the changes of oviposition period can affect population life table parameters and high significant in imidacloprid lower fecundity were found after insecticide treatment. Conclusion of this study suggested that nicotinoid at this concentration of treatment was enough to kill survivor individuals at less than this concentration or this population of S.littoralis were susceptible to those insecticides.