Sublethal effects of Angelica sinensis and Ricinus communis extracts on the growth, development and fecundity of Spodoptera exigua Hübner

The toxicity regression equations for Angelica sinensis and Ricinus communis were established, and the sublethal dosage (LC₂₀ and LC₃₀ ) effects of the two extracts on the growth, development and fecundity of beet armyworm (Spodoptera exigua Hübner) and its F₁ progeny were determined in this paper. The results suggested that sublethal dosages of the two extracts had no significant effects on development duration of 2^nd~5^th instar larvae, pupal duration or male/female pupal weight of surviving parent and F₁ progeny of S. exigua. The fecundity of parent S. exigua decreased by 21.4% and 26.5% respectively in A. sinensis LC₂₀ and LC₃₀ treatments, compared with the control. Also the fecundity of S. exigua F₁ progeny decreased by 45.4% and 61.3% respectively in LC₂₀ and LC₃₀ treatments of A. sinensis. Similarly, the fecundity of parent S. exigua decreased by 23.5% and 27.3% in LC₂₀ while that of the F₁ progeny decreased by 52.7% and 61.0% respectively in R. communis LC₂₀ and LC₃₀ treatments. While pupation and emergence rates of parent S. exigua were not significantly affected by R. communis LC₂₀ and LC₃₀ treatments, the two indices significantly decreased under A. sinensis LC₃₀ treatment. Compared with the control, A. sinensis LC₂₀ and LC₃₀ had no significant effect on pupation rate of S. exigua F₁ progeny, while A. sinensis LC₃₀ significantly decreased emergence rate of S. exigua F₁ progeny. Also R. communis LC₂₀ and LC₃₀ significantly decreased emergence rate of S. exigua F₁ progeny and R. communis LC₃₀ significantly decreased pupation rate of S. exigua F₁ progeny. After treated with LC₂₀ and LC₃₀ sublethal dosages of the extracts, adult sex ratio orders of surviving parent and F₁ progeny of S. exigua were severely distorted. Meanwhile A. sinensis and R. communis LC₃₀ dosage largely affected the adult sex ratios of S. exigua parent and F₁ progeny, with sex ratios (♀∶♂) of 1∶0.5 and 1∶2.1, respectively. Our study revealed that sublethal dosages of the two extracts had some inhibitory effects on the growth, development and fecundity of S. exigua. The study therefore provided the theoretical basis for studying the sublethal effects of plant extracts.