| Fertilizer is the key role to affect the development and nutrition characters of plants then affect the development,nutrition indexes and population dynamic of herbivorous insect that feed on the plant indirectly.Therefore,investigating effects of fertilization on plant and herbivorous insect can provide an important evidence for the management of insect pests.In this study,we use tobacco and Spodoptera litura as a model,investigated how the recommended fertilizer amount,75kg/hm2(A),90kg/hm2(B),105kg/hm2(C),120kg/hm2(D),and 135kg/hm2(E),affect the tobacco nutritional qualities and development,nutritional indices and feeding preference to S.litura.The main results followed as below.At the fertilization level of E,the plant height,pitch,maximum leaf width,maximum leaf length,leaf number,stem circumference was significantly higher than other fertilization levels of tobacco on the resettling growth stage.On the fast-growing stage,there was no significant difference on plant height,stem circumference,maximum leaf width among the C,D,E fertilization levels plots,while they were significantly higher than A&B fertilization levels plots.The plant height was 160.08 cm,which was significantly higher than other treatments.And stem circumference was12.02 cm,step was 4.06 cm,maximum leaf length was 57.06 cm,maximum leaf width was 29.18 cm on A treatment,which these agronomic traits were significantly lower other treatments on tobacco flowing stage.While,the leaf amounts there was no significance on tobacco fast-growing stage and flowing stage among the five fertilization levels plots.In summary,on the early growth stage,fertilizer applying could improve tobacco agronomic traits in certain fertilization levels,and there is a positive correlation between them.The nutrient contents of the same leaf position under five fertilization treatments were significantly different,but there was no obvious trend.The dynamics of soluble protein of three position leaves under five fertilization treatments were firstly decreased,then increased and then decreased.With the prolongation of tobacco growth time,the content of soluble sugar has an increasing trend.These results indicated that fertilizer could effects of tobacco leaves nutrient traits directly.High fertilization is more easily to improve nutrient character.In order to analysis the effect of tobacco leaves at five fertilization levels on the larval development period of the S.litura,we feed the larvae with different leaves at different fertilizer applying plots.Total larvae development time,pupa duration,sex ratio and survival rate were affected by the leaves at different plots significantly.The total larvae develop time and pupa duration was shortest on treatment D was significantly lower than other treatments,it were 17.61 d,and 10.72 d.While,the larvae survival rate and pupal duration survival rates at E plot were higher than other plots significantly.The pupal at fertilization level of A and E were significantly higher than another three fertilization levels.But there were no significant effects on pre-pupal duration,adult live longer and fecundity under five different fertilization levels.The male ratio at E was higher than other plots was 1: 0.85.The female ratio at B was higher than other plots was 1: 1.08.These results suggested that the fertilization level has an important effect on larval development period,survival rate and sex ratio.Super abundant fertilization using would induce the S.litura outbreak.In order to analyze the nutritional indices of S.litura feeding the five different fertilization level plots.The relative consumption rate in treatment E was 16.35,relative growth rate was 0.51,approximate digestibility was 90.80% in 4th,which was significantly higher other fertilization level.The efficiency of conversion of ingested food first decreased and then increased with increasing fertilization,the efficiency of conversion of digested food of B was higher than that of the other treatments.The relative consumption rate and approximate digestibility first increased and then decreased,the fertilization of D was significantly higher than other treatments in the 5th.The efficiency of conversion of ingested food and efficiency of conversion of digested food first decreased and then increased with increasing fertilization,the fertilization of E was significantly higher than other fertilization levels.The relative consumption rate increased from 0.1 on A treatment to 2.58 on C treatment and then decreased to 2.17 on E treatment.The relative growth rate increased from 0.02 on A treatment to 0.50 on D treatment and then decreased to 0.25 on E treatment.The efficiency of conversion of ingested food and efficiency of conversion of digested food of fertilization of D were34.57% and 66.57%,which was significantly higher than that of other treatments.The approximate digestibility of fertilization of A was 69.48%.The food consumption rate increased then decreased and then increased,the food utilization rate decreased then increased and then decreased,and the relative growth rate decreased from 0.21% on A treatment to 0.15% on C treatment and then increased to 0.26% on E treatment.The results indicated that the higher fertilization level was beneficial to promote the nutritional indices metabolism of S.litura.In order to investigate the feeding preference of 1st instar larvae,we fed 1st instar larvae with leaves at different fertilization levels.The results indicated that the selection coefficient of upper leaves at A,B,C,D were significantly higher than middle and lower leaves at 12h、24h、36h and 48 h.The selection coefficient of middle leaves at E was significantly higher than upper and lower leaves.The selection coefficient of middle leaves at E at 48 h was 42.5%,which was significantly different before 36 houres.The selection coefficient of upper leaves at A had the trend of increasing with the time.The A treatment had the trend of increasing with the lasting of time at 24 h,36h,48 h,which was significantly higher than other fertilization level Even there was no significantly different among five fertilizations,but the selection coefficient of lower leaves in A had the trend of increasing with time lasting.These results indicate that 1st larvae prefer to feed the leaves at low fertilizer plants. |
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