Ecology and Vectorship of the Citrus Psyllid in Relation to the Prevalence of Citrus Huanglongbing

• Main Authors: Shih-Cheng Hung, 洪士程
• Other Authors: Chiou-Nan Chen
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/06178585711084415875

博士 === 國立臺灣大學 === 昆蟲學研究所 === 94 === Huanglongbing (HLB) caused by Candidatus Liberibacter asiaticus is the most destructive disease of citrus in Taiwan. It affects most citrus species, hybrids, and cultivars. Pathogens can be transmitted by grafting and by insect vectors. Once the healthy seedlings are planted out in the field, control of huanglongbing depends on control of the psyllid vector. Huanglongbing affected 4 genera of the Rutaceae, namely Citrus, Poncirus, Fortunella and Severinia. Diaphorina citri feeds and breeds on the entire group of horticultural Citrus, with additional hosts in seven different genera belonging to the Rutaceae, namely Citrus, Poncirus, Fortunella, Severiniam, Murraya, Clausena and Feronia. Psyllids in citrus orchards showed that the population of adults had three peaks per year which were coincided with the periods of citrus flushing at spring, summer and fall. The number of adults was most abundance in the first population peak. Flight phenology of D. citri occurred from March to May when adults that emerge from nymphs and psyllid populations are highest. Citrus psyllids acquire the huanglongbing bacterium primarily in the nymphal stage, and adult psyllids arising from nymphs that feeding on diseased shoots are easy to become vectors. A single adult of D. citri can transmit HLB. Citrus psyllids are not highly efficient vectors of huanglongbing in Taiwan, and epidemics occur only when high vector populations and an extensive inoculum reservoir are present. The trend of natural infectivity during the year indicated a high proportion of D. citri collected in March and August were PCR-positive for the pathogen. The efficiency of huanglongbing transmission is related to high vector population, percentage of psyllids that carrying pathogens and vector dispersal activity. Thus, flight activity and seasonal rhythms of D. citri populations would be very important considerations for management. The epidemic pattern follows the typical sigmoidal curve. The disease is cumulative and increases with time, depending on the abundance of the vector and the availability of infected plants. It starts slowly, increases gradually year after year until it reaches the exponential stage and only then the epidemic increases rapidly. Control strategy is to prevent disease damage from exceeding that level where profit or required yield is significantly diminished. Reduce the initial inoculum and reduce the rate of infection, two major strategies can be used for managing HLB disease epidemics, and we can organize our plant disease control tactics under one or more of these overall strategies.