Effects Of Management Pattern On Aphids And Predatory Natural Enemies In Alfalfa Field

Aphids are one of the main pests that damage the alfalfa industry in Ningxia,where mainly relies on chemical pesticides for aphid control.It is of great significance for the ecosystem’s health to construct green control measures for aphids and carry out research on the environmental regulation of pests at multiple scales.In this paper,in alfalfa fields and marginal weed belts in different regions of Ningxia,by studying the species and population dynamics of aphids and predatory natural enemies,as well as their differences;the effects of different management pattern(irrigation and mowing)on aphids and predatory natural enemies in alfalfa fields,to enhance the biological control of pests of alfalfa field passing landscape regulation and rational farming technology.The main findings are as follows:(1)Population dynamics and differences of aphids and predatory natural enemies in alfalfa fields and marginal weed belts in Ningxia:The main aphid species are Therioaphis trifolli and Acyrthosiphon pisum;the main predatory natural enemies are lady beetles and lacewings,and a total of 6 species of ladybeetles and 2 species of lacewings were found,in the Yellow River Diversion irrigation district in northern Ningxia,the middle arid zone of Ningxia and the south mountainous area of Ningxia.However,there are certain differences in the species and quantity of lady beetles and lacewings between different habitats(alfalfa fields and weed belts).There were significant differences between different regions in the number of aphid predatory natural enemies and the morphology of main lady beetles.In alfalfa fields,the annual total amount of ladybeetles were 3.38 times,36.10 times,7.94 times and 6.30 times that of marginal weed belts respectively in Pingluo county,Hongsibu district,Pengyang county and Longde county,and the annual total amount of lacewings was 17.75 times,7.00 times and 3.54 times that of marginal weed belts respectively respectively in Pingluo county,Pengyang county and Longde county.There were significant differences in the numbers of aphids and predatory natural enemies and the body types of the main ladybirds between different regions,while the numbers of aphids and their predatory natural enemies in the same region varied greatly with the survey date.(2)Effects of mowing times on the populations of aphids and predatory natural enemies:mowing significantly reduced the number of aphids and lady beetles in alfalfa fields(P<0.01 or P<0.05).There were significant differences in the peak time,quantity and frequency of aphids and lady beetles in the treated alfalfa field,affecting the ratio of lady beetles to aphids in different stubbles of alfalfa.The results showed that mowing the first stubbles of alfalfa in mid-June when aphids had not grown rapidly in the mountainous area of the south mountainous area of Ningxia could significantly reduce the number of aphids.Still,it might lead to aggravation of aphids in the second stubbles.When mowing was carried out in late June,the first stubbles of alfalfa aphids did more damage,but the second stubbles of alfalfa aphids caused less damage.(3)Effects of irrigation pattern on the populations of aphids and predatory natural enemies:The irrigation pattern affects the populations of aphids and predatory natural enemies in alfalfa fields.In most periods,the number of predatory natural enemies in sprinkling-irrigated alfalfa fields was higher(1.23 times of flooding alfalfa fields),the occurrence of aphids is lower(37.79%of flooding alfalfa fields),and the number of predatory natural enemies to aphids is higher(2.20 times of flooding alfalfa fields)in the Yellow River Diversion irrigation district in northern Ningxia.The number of predatory natural enemies in flood-irrigated alfalfa fields was significantly higher in most periods in the middle arid zone of Ningxia(2.68 times and 1.73 times of sprinkler-irrigated alfalfa fields in 2020 and 2021,respectively),and in most periods of aphids(only in July 2021,the number of predatory natural enemies was significantly higher in flood-irrigated fields)occurred less(56.19%and 1.04 times that of sprinkler irrigation fields in 2020 and 2021,respectively),and the ratios of natural enemies to pests were higher(only in July 2021,the flood irrigation fields were significantly higher)(16.24 times and 72.63%that of sprinkler irrigation fields in 2020 and 2021,respectively).