| During the dormancy of pest oversummering and overwintering period,the ecological service functions of natural enemies and beneficial microorganisms play an important role in controlling the population base number of pests under different farmland landscapes.In this study,we chose Pieris melete,which oversummering and overwintering as pupae.Based on the multi-layered farmland landscape background of Jiangxi Province,we investigated the survival dynamics of diapause oversummering and overwintering populations under different landscapes.The role of farmland landscape pattern in controlling the natural predators,parasitoids,beneficial microorganisms,and their ecological pest control functions were analyzed,and the effect mechanism of farmland landscapes on the survival of the oversummering and overwintering populations of butterfly.The main results are as follows:1.Survival dynamics of oversummering and overwintering populations of P.melete under different farmland landscape patternsThe artificial Bait-card was used to monitor the surviving dynamics of the oversummering and overwintering populations of the cabbage butterfly on 8 different farmland landscapes in Jiangxi Province.The results showed that the fresh pupa in all the sites attracted a large number of natural predators and parasitoids,resulting in a sharp decline.In general,the WD population decreased gradually,instead the SD population was quickly descend.There three sites respectively of SD population occurred extinction in the middle period for 2-yr.Naturally,the survival rate of WD population(33.43±5.72%,2017;57.50±5.12%,2018)were much higher than that of SD(7.77±3.35%,2017;1.17±0.79%,2018)by the end of monitor round,and the results were consistent for 2-yr.A clear seasonal survival dynamics of P.melete diapausing pupae was illustrated in different test sites.Moreover,there were some differences in the survival dynamics of the diapause population of P.melete in each site.The model analysis found that the landscape factor had a certain correlation effect on the survival dynamics of P.melete.2.Effects of farmland landscape patterns on the parasitiods and their controlling functions of P.meleteIn order to find out the lethal factors of the diapause pupae of P.melete in different farmland landscapes,all the pupae of P.melete turned black or unhealthy were collected individually.The emerged adult parasitoids were identified using gross morphology under a stereomicroscope and combined with molecular identification.The results showed that the oversummering population of the cabbage butterfly was parasitized by two parasitoids,Brachymeria femorata and Diadromus collaris.However,the parasitic percentages of the two parasitiods varied greatly,B.femorata,was the predominant specie accounting for 100% and 97.7% of total parasitism in2017 and 2018,respectively.Due to the influence of low temperature environment,no parasitoid was collected in winter.There was no significant difference in the parasitism rate between different sites.The total parasitism rate in 2017 was 0.47%-27.66%,and in 2018 was 0-23.98%.Regression analysis showed that the correlation between the parasitism rate of various sites and the mortality rate of the cabbage butterfly was low,which indicated that the parasitoids were effective in controlling the diapause population of the cabbage butterfly,but it was not the most important key lethal factor.Analysis with related landscape factors showed that the parasitism rate of P.melete was not significantly correlated with landscape factors such as landscape diversity,non-crop habitat,forest,and cultivated land proportion,but as the non-crop habitat and forest area proportion increased,the parasitism rate also increased,however,with the increased proportion of cultivated land,the parasitism rate decreased.3.Effects of farmland landscape patterns on predators and their controlling functions of P.meleteFrom the video surveillance,we found ants were the major predator,no other predators were detected provisionally.A total of 17 species of ant samples were identified,and the most abundantly collected species was Polyrhachis dives,a large number of ant species were collected at S8.The average predation rates of the oversummering population in 2017 and 2018 were 68.41 ± 24.96% and 73.98 ±20.45%,which were significantly higher than the overwintering population predation rates(47.31 ± 22.25% and 34.18 ± 17.87%).Two-year results found significant differences in predation rates for overwintering populations in different farmland landscapes,but not significant differences in oversummering populations.The predation rate of each site was significantly positively related to the mortality rate of the cabbage butterfly,indicating that predatory was one of the key factors controlling the number of the cabbage butterfly.The predation rate was not significantly correlated with the proportion of non-crop habitat and forest area.4.Effects of farmland landscape patterns on entomopathogenic fungi and their control functions of P.meleteNaturally died individuals of P.melete were brought back for isolation and identification.A total of 206 fungal strains were isolated,belonging to 31 genera and81 species,Nigrospor was the dominant,and the species richness of S7 pathogenic fungi was the highest.In 2017 and 2018,there was no difference in the mortality rate by fungi among the overwintering populations of P.melete,but the difference in oversummering population was significant.In addition,the mortality rate by fungi(8.54%-43.88%)of the oversummering population in 2018 was significantly higher than that of the overwintering population(0-17.85%).The mortality rate by fungi was positively related to the mortality rate of pests,suggesting that the insect pathogenic fungi played an important role in the survival of P.melete.Bioassay experiments were performed on the six selected pathogenic strains,and the results showed that the mortality rate of Beauveria bassiana on the 21 st day was 73.33%,Nigrospora oryzae was 60%,and other strains were lower.The mortality rate of B.bassiana and N.oryzae were significantly better than other strains,showing a certain potential for biological control.In addition,the diversity of pathogenic fungi increased with the increaseof the proportion of non-crop habitats(such as forest)in farmland landscapes,and the increase in the area of cultivated land reduced the diversity of pathogenic fungi,and this correlation is more significant in small-scale landscape.This study clarified the mechanism of the impact of farmland landscape patterns on the survival of the oversummering and overwintering populations of P.melete,which was conducive to the comprehensive ecological management of regional pests and provided reference materials for biological control. |
