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Diaphorina citri Kuwayama (Insecta: Hemiptera: Psyllidae)





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          The Asian Citrus Psyllid that vectors a bacterial pathogen that causes Huanglongbing Disease is currently spreading worldwide and poses a severe threat to the citrus industries of many nations.  There is no effective control other than the possible development of resistant citrus varieties.  Such development requires decades to implement and is not a viable approach in the short term. As of 2011 the pest has been detected in scattered localities throughout Southern California but in very low numbers.  Also, the destructive bacterium that is associated with it was first detected in 2012.  Nevertheless, ignoring the ultimate threat, citrus is still being planted in city landscaping projects and all varieties are being widely sold throughout California


          Attempts to control this psyllid by the importation of natural enemies have begun in 1911, but the exact point of origin is unclear and the probability of success is uncertain.  This is largely due to the fact that the bite of only a single psyllid individual can inoculate the disease-causing pathogen.  Nevertheless two parasitic wasps, Tamarixia radiata and Diaphorencyrtus aligarhensis have been imported from northern Pakistan and liberated in Southern California where the psyllid occurs. Tamarixia (Family: Eulophidae) is now established.  It was first described in 1922 from specimens that emerged from the Asian psyllid on lemons in Lyallpur (modern day Faisalabad in Pakistan).  Ongoing investigations are to determine its impact on the psyllid and its adaptability to the California climate.


         Without effective natural enemies, insecticide treatments for the Asian psyllid as it advances into Inland areas can only be a temporary halt to the invasion of this pest.  There are no geographical barriers between the Inland and coastal areas of Southern California where the psyllid is now established, and therefore the insect will reinvade again and again.  The eradication effort would have been more effective if it had been carried out at sites where the pest was originally detected in the coastal areas.  Also, the psyllid, with the accompanying bacterial pathogen, has also been found in Sacramento in packages from India, and it is doubtful that such  "Innocent" mailings can ever be halted.

          In the mid-1960's a statewide Department of Biological control existed in the University of California with 40 or more professional entomologists, most with PhDs from noteworthy institutions.  Control of insect pests with the potential severity of the Asian citrus psyllid were immediately assigned to a number of specialists whose mission involved not only a search worldwide for natural enemies but also included specialists from other countries who possessed information on any development of plant resistance.  The United States Dept. of Agriculture also directly cooperated with efforts in the search and screening of natural enemies for importation.  The elimination of the Biological Control Department within the University of California system and the massive transfer of available funding to genetic engineering pursuits, have placed pest control in a very precarious situation.  Not only is the Asian citrus psyllid a major concern, but also due to the accelerated rate of invasions of exotic pests, largely through California ports, serious pests of apple, grapes, almonds and other vital agricultural crops are being detected every year.

          There are several aspects of the invasion that must be closely followed:

          1.  Will the psyllid population be able to withstand the California climate?  The Mediterranean fruit fly has been widespread in California for over 100 years, but only occasionally is detected and has never caused a problem to agriculture in the state.

          2.  As with the leafhopper that vectors a virus pathogen of oleander, will there be a quick recovery of the plants after infection?

          3.  Similarly as with the East Indian brown cricket, will local predatory fauna and climate restrictions reduce the psyllid to more inconspicuous levels in a few years?

          4.  Could California's higher latitude be an asset to reducing the severity of the disease?  In Florida by 2012 the psyllid had devastated the southern quarter of that state, but it is a lesser problem in the central primary citrus growing area.  In the citrus-growing areas of California the 32 plus degrees of latitude is much higher than Central Florida.


          5.   Will the establishment of two new parasitic wasps from India and Pakistan reduce the psyllid population low enough to reduce the threat?



The following websites also contain information on the Asian Citrus Psyllid: