Abstract:

Respiratory rates of 3－5 instar larvae of the susceptible strain (SS), near isogenic lines-resistant strain (NILs-RR), resistant strain (RR) ofthe beet armyworm, Spodoptera exigua (Hübner) to lambda-cyhalothrin were determined under the condition of 25±l℃, RH 70%， illumination 3 000 lx and photoperiod 14L∶10D. The results indicated that there were no significant differences in the respiratory rates of the same instar larvae among the three strains, and the increase of resistance level to lambda-cyhalothrin did not resulted in the change of the fundamental respiratory rate. Treated with lambda-cyhalothrin, all the larva respiratory rates of the three strains increased with the increase of treatment dose. However, the respiratory rate of the NILs-RR strain was higher than that of the RR strain, and both were higher than that of the SS strain under their respective LC₂₀ and LC₅₀ doses. The highest respiratory rate of the two resistant strains and the susceptible strain appeared at 5 h and 2 h after treatment, respectively. The high level periods of the respiratory rates in the two resistant strains were significantly longer than that of the susceptible strain. It would take 24 h and 15 h respectively for the resistant strain and the susceptible strain to recover to the initial levels of their respiratory rates. It was so inferred that correlation existed in some extent between the increasing rates of the respiratory rate and the ability of detoxification metabolism to lambda-cyhalothrin in S. exigua larvae after treatment.

Key words: Spodoptera exigua, insecticide resistance, resistant strain, susceptible strain, respiratory rate, lambda_cyhalothrin