Analysis of pest community diversity and temporal dynamics in thinned and unthinned litchi orchards

Abstract: 【Objective】Litchi is one of the most important fruits in south China. The cultivated area of litchi was increasing in recently year. Pests and diseases became more and more serious in un-thinned litchi orchard. In order to improve the environment of orchard, output and quality of litchi, the un-thinned litchi orchard must be thinned by reasonable thinning. The aim of this study was to reveal the community composition, species diversity, dominant pest species and annual occurrence of pests in thinned and un-thinned litchi orchards in Guangzhou, and to provide a theoretical basis for proper application of thinning and green control of pests.【Methods】A survey was conducted on the pest species diversity in thinned and un-thinned litchi orchards in Guangzhou from January to December in 2016. Some larva were collected and reared in laboratory. All specimens were identified by morphological characteristics and molecular biology and some of that we cannot identify were sent to taxonomists. Specimens were saved in Plant Protection Research Institution, Guangdong Academy of Agricultural Sciences. The pest community compositions, species diversity, dominant pest species and annual occurrence of dominant pests in different orchards were analyzed. And also, the number of species, relative abundance, Margalef richness index, Shannon diversity index, Pielou evenness index and Simpson dominance index were calculated.【Results】A total of 61 species were recorded, which belong to 35 families, 7 orders in un-thinned litchi orchard. The number of Hemiptera pests in the un-thinned litchi orchard had an absolute dominance. In thinned litchi orchard, there were 39 species belonging to 26 families and 6 orders and the Lepidoptera pests had the greatest species abundance. The number of pest individual abundance and species in un-thinned litchi orchard was obvious more than that in thinned litchi orchard. The Lepidoptera had the highest Margalef richness index, followed by Hemiptera and Coleoptera, while Isoptera and Thysanoptera were the lowest in un-thinned litchi orchard. Shannon diversity index decreased in order of Hemiptera, Lepidoptera, Coleoptera, Acarina, Diptera, Thysanoptera and Isoptera. The highest Pielou evenness index was Acarina, then Hemiptera and Coleoptera. The Diptera had the highest Simpson dominance index, followed by Acarina in un-thinned litchi orchard. In thinned litchi orchard, Lepidoptera also had the highest Margalef richness index, followed by Hemiptera and Coleoptera, and Thysanoptera was the lowest. The Shannon diversity index decreased in order of Lepidoptera, Hemiptera, Coleoptera, Diptera, Acarina and Thysanoptera. The Hemiptera had the highest Pielou evenness index, followed by Diptera. The Acarina had the highest Simpson dominance index, followed by Diptera.There were two obvious peaks in individual abundance with the main peak occurring between April and October. In the un-thinned litchi orchard, only one peak in species richness occurred in September. However, there were two peaks in species richness occurred in un-thinned litchi orchard from April to May and September. Different micro-environments within the orchards could have a different community composition. The dominant pest species in un-thinned litchi orchard were Conopomorpha sinensis, Thalassodes immissaria, Tessaratoma papillosa, Litchiomyia chinensis and Unaspis yanonensis. Unlike that though, the dominant pest species were Conopomorpha sinensis, Thalassodes immissaria, Tessaratoma papillosa, Protaetia brevitarsis and Oligonychus litchii in thinned litchi orchard. In un-thinned litchi orchard, the number of individual abundance of dominant pests were increasing with the increase of temperature, which reached the first peak between April and May, then the number of Thalassodes immissaria, Tessaratoma papillosa and Litchiomyia chinensis decreased from the flowering phase till the fruitlet phase over. From July to September, the number of Thalassodes immissaria, Litchiomyia chinensis and Unaspis yanonensis started rising again and reached the second peak at September. The pattern of annual occurrence of Conopomorpha sinensis was a humped-shaped model with a peak at August, and the number of Conopomorpha sinensis declined sharply with the end of longan harvest. The occurrence of Conopomorpha sinensis was consistent with the phenological period of litchi growth. The patterns of annual occurrence of dominant pests in thinned orchard were the same as that in un-thinned litchi orchard, but the number of dominant pests in thinned litchi orchard was less than that in un-thinned litchi orchard. The number of Thalassodes immissaria, Tessaratoma papillosa, Protaetia brevitarsis and Oligonychus litchii reached the first peak between April and May, and the second peak appeared between September and October. The annual occurrence of Conopomorpha sinensis was also a humped-shaped model with a peak in July.【Conclusion】The un-thinned litchi orchard has higher pest species diversity. After reasonable thinning, the pest species and quantity both decreased significantly in thinned litchi orchard. In the meantime the ecological environment, the output and litchi quality in the thinned litchi orchard were obviously improved. There was a strong correlation between the pest occurrence and litchi phenology. Therefore, a pest control should be carried out according to different phenological growth period of litchi. In addition, it is necessary to take an extensive and deep investigation about the species and biodiversity of natural enemies in the orchard, to provide scientific references for green production.