| Myzus persicae(Sulzer)and Lipaphis erysimi(Kaltenbach)are important pests of crops with long-time damage and great occurrence quantity.The two species of aphids can colonize large number of plant species,e.g.,Brassicaceae,Solanaceae,and Compositae.In addition,they can also transmit a variety of plant viral during feeding.A.gifuensis is the dominant endozoic natural enemies of aphids,and it has stronger control on M.persicae and L.erysimi.At present,the research on A.gifuensis mainly focuses on the large-scale indoor propagation.However,there have been few reports on the control of A.ifuensis on winter aphids and the application of field release modes.Based on this,this paper took the two main winter aphids in Guizhou Province as the research object,compared the growth and reproduction of two kinds of aphids on different winter hosts,studied the control effect of A.gifuensis on aphids of different winter hosts,and further analysized and compared the insects decresae rates of aphids,the parasitic rates of A.gifuensis and the eclosion rates of mummified on the winter hosts.Finally,the control effects of different release modes of A.gifuensis were explored on the field.The main results of this dissertation are as follows: 1 Investigation on the occurrence regularity of M.persicae and L.erysimi in winter hostsTo clarify the harm of the two aphids to the winter hosts.The author investigated systematically the occurrence regularity of aphids on winter crops in Jinhua town of Fenggang county and Jiancha town of Dejiang county.The results showed that the main crops that were damaged by M.persicae were Brassica juncea(L.)Czern.et Coss.and Brassica pekinensis(Lour.)Rupr.and Raphanus sativus L.and Brassica campestris L.and Brassica campestris L.var.purpuraria L.H.Bailey.The highest rate of damage of M.persicae in Jiancha Town was 62.00%,and Jinhua town was slightly lower,accounting for 52.67%.The incidence rates of M.on R.sativus was the highest among the five kinds of hosts,followed by B.juncea.Among them,the number of M.persicae was 167.16 per plant,followed by B.juncea,which was 147.08 per plant.And there was no significant difference between B.campestris and B.campestris var.purpuraria in Jiancha town.The results of Jinhua town survey showed that the maximum amount of M.persicae on R.sativus was 135.28 per plant,followed by B.campestris,and the number of aphids was the least in B.campestris var.purpuraria.Through the analysis of the data of Jiancha town and Jinhua town,it was found that the damage of the Jiancha town was higher than that of Jinhua town on B.juncea and R.sativus,while that of the other three species was lower than that of Jinhua town.The survey results of L.erysimi showed that there was no significant difference in the total aphids between the two regions.In addition to the population of L.erysimi on R.sativus in Jiancha town,the number of other crops was lower than that of the evolved town.Consistent with M.persicae,the main damage of L.erysimi are R.sativus and B.juncea,and the highest number of aphids on R.sativus is 59.05 per plant in Jiancha town and Jinhua town was 32.88 per plant.In summary,it is known that both M.persicae and L.erysimi are mainly harmful to R.sativus and B.juncea.Therefore,it is important to control aphids on the above two crops.2.The control of A.gifuensis on aphids in different winter hostsThe population changes of the M.persicae,the control effect of A.gifuensis on M.persicae,and the eclosion rate of mummified aphids among seven winter hosts were explored under natural conditions.The results showed that the different natural growth of M.persicae populations on seven host plants was expressed follow as: Nicotiana tabacum cv.K326 > B.juncea > B.juncea var.gracilis > B.napus > R.sativus > B.campestris var.purpuraria > B.pekinensis.The parasitic rate of A.gifuensis on B.juncea is 70.56%,which is significantly higher than other winter hosts.The eclosion rates of mummified aphids are all higher than 70% on seven winter hosts.Eclosion rate of A.gifuensis is the highest on B.juncea(97.33%),while the lowest is on R.sativus(72.87%).In conclusion,M.persicae feeding on seven hosts could be parasitized by A.gifuensis and all have a higher eclosion rate of mummified aphids,but the natural growth population of M.persicae and the eclosion rate of A.gifuensis is highest on B.juncea.The population changes of the L.erysimi,and the reduce rates of L.erysimi and parasitic rate and the eclosion rate of mummified aphids among 6 winter hosts were compared via whether the release of A.gifuensis or not.The results showed that the growth trend of L.erysimi on R.sativus is significantly better than that of other five winter host plants in the absence of natural enemies.After A.gifuensis was released,on the 40 th day,the reduce rate of L.erysimi is highest in B.napus,followed by B.juncea,and the worst was R.sativus.The parasites rate of L.erysimi was the highest on B.juncea,which was 47.49% and obviously higher than the other 5 winter hosts.The eclosion rate of mummified aphids was higher than 80% on 6 winter host plants.The experimental results show that M.persicae and L.erysimi can be parasitized by A.gifuensis and can eclosion.Therefore,we can release A.gifuensis to control aphids on winter crops.Make it possible to establish natural populations in the field.and reduce the spread of aphids and damage to spring crops.3.Study on the control effect of A.gifuensis release mode on M.persicae in the fieldsTo explore the control effect of M.persicae via the auto-sustained release and adult bee-release modes of Aphidius gifuensis in the field.The effects of two kinds release mode on the populations of M.persicae in rape and tobacco fields were systematically investigated from March to May 2017 in Jiancha town Dejiang county of Guizhou province,and calculate the control effect based on the survey data.The results show that there are two significant differences between the amount of M.persicae per 10 plants ranged from 72.67 to 115.73 heads on the rapeseed field and the tobacco field as from 15.33 to 19.40 before A.gifuensis was released.The relative control effect of adult bee-release method was 53.12% in rape field and that in tobacco field was 52.81% after release,and the control effect was better than that of auto-sustained release method.However,the way of auto-sustained release in the late stage was as high as 76.76% for the prevention and control of M.persicae,and the persistence of control was strong.In summary,the two release modes have their advantages.Adult bee-release method can control the population of aphids in a relatively short period of time.However,the auto-sustained release method has a good persistence to the control of aphids.Therefore,it is suggested that we can reasonable combination of two release modes to improve its control effect when we use A.gifuensis to control M.persicae in the future. |
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