Abstract:
The beet armyworm (Spodoptera exigua Hübner) is an important pest of many
agricultural crops all over the world. Most of the sugar beet growing regions in Iran are
infested. In this study, the acute lethal effects of Pyriproxyfen, Spinosad, and Indoxacarb
as well as sublethal effects of Pyriproxyfen on the 1st instar S. exigua were assessed by leaf
dip bioassay method. Mortality was recorded 48 hours after treatment. LC50 and LC90
values for Spinosad were 0.096 and 0.252 mg ai l-1, respectively, and for Indoxacarb, they
were 2.510 and 38.828 mg ai l-1, respectively. The LC50 value for Spinosad was 26 times
lower than that of Indoxacarb. Preliminary experiments revealed that Pyriproxyfen did
not cause acutely lethal effects on the beet armyworm larvae even following exposure at
recommended doses. Pyriproxyfen, however, did show considerable delayed effects
against this pest. Significant differences in biological, reproductive, and population
growth parameters were found in Pyriproxyfen treated insects in comparison with the
control insects. Population growth parameters including net reproduction rate (R0
), gross
reproduction rate (GRR), intrinsic rate of population increase (rm), and finite rate of
population increase (λ) were reduced by 14.7-, 6.63-, 2.33-, and 1.09-fold, respectively,
following Pyriproxyfen exposure. Additionally, mean generation time (T) and doubling
time (DT) of the population were increased by 1.12- and 2.3-fold, respectively.
Keywords: Insecticides, Lethal effects, Life table, Spodoptera exigua, Sublethal effects.
