Study On The Diversity Of Insect Species Under Different Grassland Utilization Patterns In Guizhou

The sampling sites chosen for this study included four different grassland utilization patterns,namely shrub meadow,grazing grassland,no grazing grassland and abandoned farmland,in Xingsu Township,Dafang County Guizhou Province,China.From September 2018 to August 2019,through field investigation(sampling and field measurement)and indoor identification and mathematical statistical analysis,the characteristics of grassland plant community,insect community and their seasonal dynamics and the occurrence and damage of Mythimna separate Walk were investigated under four different grassland utilization patterns.The main results are as follows:A total of 52849 insect samples,belonging to 17 orders 85 families 288 genus 354 species(including 78 new record species for Guizhou Province),were collected and found by means of net sweeping,trap,yellow disk trapping,lamp trapping,sample line for butterfly and random collection methods.The dominant groups of grassland insects were different under different grassland utilization patterns,and Hymenoptera and Diptera were co-dominant groups.The dominant groups of shrub meadow were Hymenoptera and Diptera,the dominant groups of grazing grassland and no grazing grassland are Hymenoptera,Diptera and Coleoptera,while the dominant groups of abandoned farmland are Hymenoptera,Diptera and Homoptera.The dynamics of insect individual population is basically showed "bimodal type".The first peak appeared in spring and early summer,and the second peak appeared in August and September at the turn of summer and autumn.The insect Shannon-wiener diversity index of shrub meadow,no grazing grassland and abandoned farmland was the lowest in December,while that of grazing grassland was the lowest in May;the highest values of grazing grassland and no grazing grassland appeared in September,and the highest values of scrub meadow and abandoned farmland were respectively in June and August;and the insect Shannon-wiener diversity index showed a bimodal change in shrub meadow and no grazing grassland,while a three-peak change in grazing grassland and abandoned farmland.The calculation results of insect family diversity index showed that the Shannon-wiener index,effective diversity index,Pielou evenness index and family abundance of all patterns were abandoned farmland > no grazing grassland > grazing grassland > shrub meadow,Margalef's index of all patterns were abandoned farmland > no grazing grassland > shrub meadow > grazing grassland,and Simpson index of all patterns were shrub meadow > grazing grassland > no grazing grassland > abandoned farmland.The similarity of insects under different grassland utilization patterns was at a moderate level,with the similarity index between 0.50 and 0.75.A total of 150 species of plants,belonging to 55 families 120 genera,were also found.The main vegetation is Compositae,Rosaceae,Azaleaceae,Gramineae,Leguminosae and Cyperaceae,with species number accounts for 50.33% of the total.Among them,the number species of Compositae are the most(24 species),accounted for 16.00% of the total.Spearman correlation analysis between insect diversity and environmental factors showed that: soil temperature,air temperature and the number of plant species in shrub meadow are the main environmental factors affecting insect diversity index and insect individual number;the family abundance and individual number of insects in grazing grassland are most significantly affected by environmental factors;the index of insect diversity and the number of insect individuals in no grazing grassland are most obviously affected by soil temperature,air temperature and plant height;and the index of insect diversity and the number of insect individuals in abandoned farmland are affected by soil temperature,air temperature and the number of plant species.The occurrence of Mythimna separate Walker in the study area is characterized by "fast coming,fast going,strong momentum and strong regularity".The occurrence period in study area is about one month.We should pay attention to the monitoring of the invasion time and quantity,and pay attention to the physical trapping and killing of the adults,so as to control the number of the Mythimna separate Walker at a low level.