| The Asian citrus psyllid (ACP), Diaphohna citri Kuwayama (Hemiptera:Psyllidae), feeds on Murraya and citrus, the species of Rutaceae, and transmits citrus huanglongbing (HLB), causing tremendous lost to the citrus industry worldwide. In the present research, D. citri was studied on its biological characteristics such as the morphology and adult behavior, the host preference by adults, and the variation of super cooling and freezing points of the ACP over the overwintering period. At last, the study focused on isolation, identification and characterization of the fungal natural enemies against D. citri in Murraya groves. The main results are as follows:(1) D. citri eggs were 0.25±0.011mm in length and Mango-shaped with both slightly apiculate ends. With the growth of nymph instar, their body color is darkening and the size is increasing as well. The body length of five different stages from the 1st to 5th instar were 0.304±0.022 mm,0.46±0.035 mm,0.675±0.022mm,1.038±0.004 mm and 1.563±0.004 mm, respectively. It costed about 17 d for the psyllid to develop from newly-laid eggs to adult emergence at 27±1.5℃. The female could only be identified from the male by the preproduction organs. The preference of adult D. citri among 13 citrus varieties was determined in two types of experiments:A. alternative-choice experiment where a pair of detached shoots from different citrus varieties were put together for choice, B. multi-choice experiment where the detached shoots of all tested citrus varieties were put together for choice. The results showed that the adults of D. citri prefered to feed on the shoots of Citrus sinensis Osbeck cv. Newhall Navel Orange, Citrus tangerina Tanaka cv. Fuju and Citrus reticulata×Citrus grandis cv. Page, in comparison to the other tested varieties of citrus.(2) The super cooling point (SCP) of D. citri adults were is from -17℃ to -18℃, indicaing a strong tolerance of the psyllid to low temperature. Freezing temperature stress induced lower SCP for D. citri adults. The biochemical analyze of the groups of adults with different SCP suggested that integrated water, trehalose and amino acid play a key role in the decrease of SCP, conferring to adults more tolerance to low temperature.(3) Seven fungal isolates pathogenic to D. citri are FJAT-9620, FJAT-9621, FJAT-9622, FJAT-9623, FJAT-9624, FJAT-9719 and FJAT-9720, killing D, citri adults in mean mortality of 36.7%,6.7%,73.3%,3.3%,6.7%,83.3% and 50%, respectively. Based on examination under scanning electron microscopy and analysis of ITS sequces, the isolates such as FJAT-9620, FJAT-9621, JAT-9622, FJAT-9624 and FJAT-9719 were identified as Beauveria bassiana, while FJAT-9623 and FJAT-9720 were Beauveria asiatica and Lecanicillium attenuatum, respectively.(4) The further research on the biological characteristics of B. bassiana FJAT-9620, FJAT-9622, FJAT-9719 and L. attenuatum FJAT-9720 with different toxicity to D. citri showed that the PPDA culture medium was more suitable for the growth of fungus than PDA and SDAY according to hyphae growth rate, spore-bearing yield and bourgeon rate of spores.The determination of extracellular protease, extracellular chitinase and extracellular lipase produced by 4 fungal isolates suggested the motality of adults was correlated in different degrees with extracellular protease and extracellular lipase levels in these fungus. Influence of desiccation, ultraviolet, temperature and humidity on B. bassiana FJAT-9620, FJAT-9621, FJAT-9719 and L. attenuatum FJAT-9720 was investigated. The results revealed that the sprouting of these four strains was sensitive to the increasing concentration of PEG2000 and 254nm ultraviolet radiation. The optimum growth temperature for these fungi ranged from 25℃ to 30℃, in which the tested fungi also got a desirable infection to D. citri adults. High relative humidity is needed for fungi to infect D. citri adults. Infection by the fungi could not occur under the relative humidity less than 60%. |
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