| The experiments were carried out to determine the pesticide-toxicity to 3rd instar larvae of experimental Plutella xylostella. The effects of Abamectin susceptibility were studied to 3rd instar larvae of the Plutella xylostella due to environmental facts, temperature, humidity, host plant and Imidacloprid. The Abamectin susceptibility to the 3rd instar larvae of Plutella xylostella from FuZhou suburb were also tested. The experimental results are presented as follows:(1) Under the conditions of 25±1℃, 70-80% R. H. and 14L: 10D, the Abamectin LC50 to experimental Plutella xylostella was estimated as 0.00647μg/ml. By contrast, Chlorpyrifos and Profenofos, it presented the lower toxicity to the experimental Plutella xylostella.(2) Due to the variations of temperature(X1), humidity(X2) and different dilution of Abamectin(X3) , the function equation is estimated for the adjustment mortality rate (Y) as:Y=-2.197×10-3+6.071×10-2X1—9.962×10-4X12—7.467×10 (-3) X22—2.450×10-8X32(r=0.9713, F=12. 53, P=0. 03241<0. 05)Due to the raising temperatureX1) and humidity(X2) , the function equation is estimated for the CarE activity index (Y) of the experimental Plutella xylostella as:Y=-9.274×10-2+1.812×10-1 X2—7.688×10-5X12—2.960×10-2X22(r=0. 9272, F=8.167, P=0. 03520<0.05)(3) Due to the habit of feeding different host plants the CarE vigor of the experimental Plutella xylostella was varied, and the susceptibility to Abamectin was significant varied. The LC50 values of Abamectin to the 3th instar larvae fed with cabbage, pakchoi, brussels sprouts, mooli and Chinese kale were 0.00536μg/ml, 0.00585μg/ml, 0.00743μg/ml, 0.00799μg/ml and 0.00884μg/ml respectively.(4) The toxicity study was conducted to test the Imidacloprid influence on the Abamectin susceptibility of Plutella xylostella. The linear regression equation for the relationship between the LC50 (dilution multiple) of Abamectin to the experimental Plutella xylostella (Y1) and the dilution multiple of 20% Imidacloprid (X) was estimated as: Y1=14205-12491n(X); and that for the CarE activity index of the experimental Plutella xylostella due to Imidacloprid (Y2) and the dilution multiple of 20% Imidacloprid was as: Y2 =-0. 0804+0. 0196 ln(X).(5) Be opposite in the recommendation density, the 3rd instar larvae of Plutella xylostella which from Fuzhou suburb had presented 4-6 times resistance to the Abamectin. |
