Sublethal Effect Of Fipronil And Abamectin On Diamondback Moth (Plutella Xylostella (L.))

In this thesis, the sublethal effect of fipronil and abamectin on diamondback moth (Plutella xylostella) 3^rd instar larvae was studied. Also, the effect of the 2 insectcides on the short time high temperature tolerace of the tested insects was investigated.After being treated at the sublethal dosages, the mortality of tested insects increased with fipronil concentration and observation time. Within the same treatment, the average feeding amount of dead individuals was lower than that of living ones. And the differences expanded as fipronil dosage rose. In CK, the average feeding amount of dead individuals was 1.20 leaflets, less than half of that of living ones which was 2.08 leaflets. But in the 12.50 mg/L fipronil treatments the respective feeding amount were 0.34 and 2.13 leaflets, where the gap was over 5 times. For the total feeding amount of all tested insects within one dosage treatments, compared with CK, 0.20mg/L fipronil could increase that by 22%, but the contrary was seen in all other treatments. In 0.39mg/L fipronil treatments, the total feeding amount was inhibited by 21% and that in 12.50mg/L ones, that was 70%. The pupation rate or average pupae weight decreased a little as fipronil dosage increased, although that was not significant. The pupation period increased as fipronil doasage rose. In CK, the average pupation period was 110h. Meanwhile, in 6.25mg/L treatments that was extended to 177.6h (p<0.05). No effect of fipronil treatment on adult emergence was found.Just the same as fipronil, the mortality after abamectin trating increased with dosage or observation time. Within each treatment, the average feeding amount of dead individuals was significantly lower than that of living ones and the gap enlarged with abamectin dosage. In CK, the average feeding amount of dead ones was near 1/3 that of living ones, but in 9.0mg/L abamectin treatments the ratio was 40. Abamectin under all the chosen dosages could inhibit tested insects feeding and the inhibition rate increased with the applied dosage. In 0.14mg/L treatments, the total feeding amount was 6.2% lower than CK, but in 9.0mg/L treatments that was 93.8%. After abamectin treatment, the pupation period and average pupae weight were changed a little but not significant. The pupation rate and adult emergence rate in all treatments except 0.14mg/L treated ones were significantly lower than those in CK, but no significant differences were found among the involved treatments.Treat the insects at 35℃ temperature for 0.5h showed protection role in insect survival,...