| Tobacco-rice rotation cropping system is a alternating cultivation mode of tobacco and rice planted in the same field one after another,in which tobacco is planted in the Spring-Summer season while rice is planted in the Summer-Autumn season,respectively.Previous studies have showed that the number of brown planthopper（BPH）,Nilaparvata lugens（St?l）population in tobacco-rice rotation cropping area was significantly lower than that in rice continuous cropping area.However,the ecological mechanism of the inhibitory effects of tobacco-rice rotation cropping system on the population growth of N.lugens was not yet studied.To understand the mechanism of the system mentioned above,several laboratory experiments were conducted as follows:1).pot experiments were carried out to verify the nicotine uptake ability of rice from the nicotine residual soils,and then the effects of nicotine concentration,rice growth period and rice varieties on nicotine uptake by rice were studied.2)Effects of exogenous nicotine on the feeding behavior of BPH were studied by using electrical penetration graph（EPG）,as well as the interference effects of nicotine on the feeding behavior of BPH was verified by artificial diet technology.3)Motrtality Table method was used to study the multi-generation population changes of BPH fed on rice which were treated with with 100 ppm,10 ppm and0 ppm nicotine through root irrigation.by Motrtality Table.4)Field enclosure experiments were also conducted to study the population dynamics of BPH in tobacco-rice rotation cropping field and rice-rice continuous cropping field,and the damage of BPH to rice was evaluated after 2-3 generations of population expansion.The main results are summarized as follows:1.Nicotine content in rice tissues treated with different treatments was quantitatively analyzed by liquid chromatography/mass spectrometry（HPLC-MS/MS）.The results showed that rice could absorb nicotine from the soil.The highest nicotine content was in the root,followed by the stem,and the lowest was in the leaf.The nicotine uptake of rice and the nicotine concentration in soil were positively correlated.The nicotine content in rice tissues of seedling stage was higher than that of maturity stage,and the nicotine uptake of different rice varieties were different due to their different transpiration rates.2.The effects of different nicotine concentrations on feeding behavior of BPH were recorded and analyzed by piercing potential mapping technique.All typical electrical waveforms were generated by BPH feeding on rice plants treated with nicotine.The wave period of non-penetrating wave（NP）of treatment group was longer than that of control group by 41.17%-580.56%.The wave period of path wave（PW）in treatment group was onger than that of control group by 42.38%-69.15%l.The wave frequency of PW of treatment group was significantly lower than control group.The complete and average wave period of phloem feeding waveform（N4）was decreased by 23.62%-57.21%compared with the control group.The wave period and frequency both of NP and PW of the treatment group were significantly increased as nicotine concentration increasing in EPG records of BPH fed on artificial feed bags.The wave period of feeding wave（I）of BPH was decreased by 32.94%-94.32%as the nicotine concentration increase.3.BPH were reared for 7 generations fed on rice treated with different nicotine concentrations.the developmental duration of BPH nymphs were significantly prolonged from the second to fifth generations.The longevities of BPH adults in the treatment group was significantly shortened,response to 3rd,4th,5th and 7th generations,.The sexual ratios were not significantly different between treatment groups and control groups in each generation.The number of eggs per oviposition of per BPH female of treatment groups were significantly lower than that in control group during the second,third and fifth generations.In the first five generations,the intrinsic rate of increase of BPH population of the treatment groups was lower than the control groups.4.The developmental stage of second-grade ovaries of female BPH fed on the rice treated with 10 ppm and 100 ppm of nicotine was delayed by 1 day and 2 days,respectively,compared with the control group.The developmental stage of grade III and IV ovaries in the treatment group was delayed by 2 days compared with the control group.When the newly hatched nymphs of BPH fed on rice treated with 1000 ppm nicotine after 13 days,the oviducts of most female adults were shorter,thinner and more transparent than control groups.After feeding to 17th day,the eggs were developed,however,most ovarian tubules were still in opalescent transparent phase and gathering.The effects of 1000 ppm nicotine concentration on the reproductive capacity of three mating combinations of BPH were studied by comparing control treatment.The result showed that number of eggs per oviposition per female of♂n×♀CKand♂n×♀n groups was significantly deceased by 20.8%and 56.5%compared with the control group;and the hatching rate of eggs of these two combinations were also significantly deceased by 31.70%and 30.46%.5.Population dynamics of BPH was monitored quantitatively by using enclosure cages which were set on the tobacco-rice rotation field and rice-rice cropping area,ten samples were set in total and each sample with five cages.The same number of successful mating BPH females were placed in each cage simultaneously.After 40 days,the number of BPH in rice-rice cropping area was 4.17 times of tobacco-rice rotation area.The sexual ratio of BPH adults of tobacco-rice rotation area was 1.51,higher than that in rice-ricecropping area（0.83）.The proportion of unfertilized eggs in tobacco-rice rotation area was significantly higher than that in rice continuous cropping area.The 1000-grain weight of rice in tobacco-rice rotation area was 34.62%heavier than that in rice continuous cropping area.The yield per cage in tobacco-rice rotation area was 24.79%higher than that in rice continuous cropping area. |
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