Screening And Application Conditions Of Highly Pathogenic Entomopathogenic Nematodes In Loxostege Sticticalis

The beet webworm,Loxostege sticticalis(Lepidoptera: Pyralidae)is a major agricultural pest worldwide,its larval pest occurs rapidly,density is concentrated and huge,and very serious regional damage,resulting in crop yield reduction,or even extinction,will also affect the growth of pasture,seriously affecting the production and quality of agricultural products and livestock in China,and the massive use of chemical pesticides,easy to lead to environmental pollution,food safety,pest resistance,etc.Therefore,biological control of L.sticticalis is essential.Entomopathogenic Nematode(EPN)is a new type of biological agent with the advantages of host specificity,wide host range,and safety to human and animal,which is widely used for biological control of pests.In order to clarify the control effect of different entomopathogenic nematode strains on L.sticticalis and to screen out entomopathogenic nematode strains with good broad-spectrum insecticidal effect and market development potential,this paper used L.sticticalis as the research object and measured the nematodes of Steinernema and Heterorhabditis by bioassay method in indoor.The two nematode strains with the strongest pathogenicity were screened out,and the effects of different ages and environmental factors on the pathogenicity of the dominant strain were determined.The main results of the study were as follows:1.We ried out the pathogenicity of six entomopathogenic nematode against beet webworm larvae.The results show that,entomopathogenic nematode Steinernema carpocapsae SFSN,S.ceratophorum ScALL,S.ceratophorum XH-4,Heterorhabditis beicherriana LF,H.beicherriana D26-6,S.sp.YNb33 D7-15 administered at doses of 100 IJs / worm,the corrected mortality rate was 100.00%,92.41%,84.81%,74.69%,70.58%,and 58.48%,respectively.Among them,the lethality rate of S.carpocapsae SFSN and S.carpocapsae ScALL can reach more than 90%,and there is no significant difference between them,so these two entomopathogenic nematodes are considered the dominant strains for the control of borer larvae.2.We determined the sensitivity of beet webworm larvae of different instars to two dominant entomopathogenic nematode strains,S.carpocapsae SFSN and S.carpocapsae ScALL.The results showed that the smaller the age of the beet webworm,the faster the death rate and the higher the nematode was at the same concentration.S.carpocapsae SFSN kills 100% at 60 h,and S.carpocapsae ScALL achieves 90.56% at 72 h.It can be concluded that 3rd instar larvae are most sensitive to nematodes,followed by the 4th instar and 5th instar larvae are the least sensitive,indicating that as the larvae grow and develop.3.We clarified the lethality of S.carpocapsae SFSN and S.carpocapsae ScALL at different concentrations of beet webworm larvae.At 120 h,the lethality was 100% at 60 IJs / worm,100 IJs/ worm,with no significant difference between them,ScALL was 91.25% and 10 IJs / worm,respectively,at the concentration of 100 and 80 IJs / worm was 60 IJs and 80 IJs,respectively.4.We explored the optimal temperature of S.carpocapsae SFSN and S.carpocapsae ScALL at optimal applied concentrations.At 21℃and 25℃,the mortality rate of the two entomopathogenic nematodes was 98.65%,94.23% and 93.60% and 89.23%,respectively,and either too high or too low temperature could significantly affect the infection efficiency.Therefore,21 to 25℃ is the suitable environmental temperature for the infection of two entomopathogenic nematodes.