| Alfalfa is a characteristicindustry in Ningxia and plays an important role as an economic pillar in agricultural development.However,aphids have become one of the most serious pests of alfalfa with the intensification of alfalfa planting,chemical control will cause a series of resistance problems.In order to establish a set of green management mode suitable for alfalfa aphid control in Ningxia,this paper evaluated the resistance of different alfalfa varieties to Therioaphis trifolii and Acyrthosiphon pisum in Ningxia,and the feeding behavior of T.trifolii and A.pisum on different alfalfa varieties were explored by EPG(Electrical Penetration Graph)technology,the leaf structure of alfalfa varieties and the changes of alfalfa biomass under aphid stress were analyzed,and the control effect of alfalfa varieties and natural enemies on aphids were determined and compared.The effects of farmland landscape pattern on aphids and predators in alfalfa field were also discussed.The main research results are as follows:(1)Resistance evaluation of different alfalfa resources to aphids:The aphid resistance levels of different varieties in the field and laboratory were evaluated by aphid ratio method.The results showed that Algonquin was highly resistant to aphids in the field and laboratory.Santory was moderate resistance;Surprising was highly sensitive.In the field,fifty alfalfa resources resistant to aphids were evaluated indicate that seven varieties were highly resistant,twenty cultivars were resistant,thirteen cultivars were moderately resistant,five cultivars were susceptible and five cultivars were highly susceptible.The results showed that there were significant differences in the number of pests and natural enemies in the field between resistant and susceptible alfalfa resources(P<0.05).(2)Determination of aphid feeding behavior and leaf structure on different alfalfa varieties:The decrease rate of high-sensitive variety Surprising alfalfa variety aboveground biomass was the highest damaged by aphids,the biomass loss was significantly higher than other alfalfa varieties after aphids feeding(P<0.05).EPG technique was used to monitor the feeding behavior of spotted aphids T.trifolii and A.pisum on three alfalfa varieties.The results showed that the duration of E1 wave of spotted T.trifolii and A.pisumon the resistant variety Algonquin was the longest,32.14 min and 104.66 min respectively.The duration of E2 wave in the high-sensitive variety Surprising was significantly higher than other two alfalfa varieties(P<0.05),and the duration were 14.33 min and 15.81 min,respectively.The thickness of upper and lower epidermis of leaves of different alfalfa varieties was compared by paraffin section.The results showed that the resistant varieties were significantly higher than the susceptible varieties.In summary,the decline rate of aboveground biomass and leaf thickness of alfalfa were related to the resistance of alfalfa varieties fed by aphids.(3)Combined effect of alfalfa varieties and natural enemies on aphids control:different types of natural enemies were used to isolate and cover the aphids.The population number of aphids and natural enemies in the cage were investigated to calculate the population growth rate of aphids.The results showed that the number of aphids of the closed cage(no natural enemies)>the restricted cage(parasitic natural enemies to control aphids)>the false cage(predatory and parasitic natural enemies to control aphids).It was concluded that predatory and parasitic natural enemies could significantly inhibit the aphid populations under the combined action of field,and the control effect on aphid populations was the best.The control effect of restricted cage(parasitic natural enemy to control aphids)on fourteenth day was better than that on seventh day,but there was no significant difference amongdifferent alfalfa varieties on seventh day,and fourteenth day(P>0.05).(4)The effect of cropping landscape pattern on the population dynamics of alfalfa aphids and predatory natural enemies:The field survey of aphids and natural enemies in four areas with large planting area of alfalfa in Ningxia.This study was conducted the total number of predatory natural enemies were 56.5 per 20 nets,which were 45.70%ladybugs,28.52%predatory bugs and 14.06%spiders of the total number of individuals respectively.In Tongxin and Hongsipu County,the numbers of predatory natural enemies were not significantly correlated with the proportion of alfalfa and corn.However,in Pingluo and Huinong County,the number of predatory natural enemies were positively correlated with the proportion of corn(P<0.05),and negatively correlated with the proportion of alfalfa(P<0.05).Alfalfa aphid populations in Hongsibao and Tongxin County were higher than in Pingluo and Huinong County.The analysis showed that the complex farmland landscape pattern provided food sources and habitats for predators,and plays an important role in protecting predators during alfalfa growth period. |
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