Asian citrus psyllid (ACP) and citrus greening disease

Contributed by Nguyet Kong

The beneficial bacteria in the citrus tree is actually the Asian citrus psyllid (ACP), a pest that is the carrier spreading huanglongbing (HLB)

The Asian citrus psyllid (ACP), which spreads the pathogen believed to cause citrus greening disease, may be playing a role in Florida’s devastating outbreak. It is also found in Southern California too where the state of California is monitoring the spread. The ACP is a tiny mottled brown insect that is about the size of an aphid. ACP attack all different types of citrus and it actually aims for the new leaf growth where it injects the toxin that causes the new leaf tip to twist or burn back. The more serious damage is causing huanglongbing (HLB) disease, which is citrus greening that causes the citrus tree to die within 5 to 8 years with no cure. It causes the fruit to be asymmetrically with aborted seeds and bitter juice. A few other symptoms include unique yellow leaf mottling that is not the same on both sides of the leaf and the shoot and branch of the tree to turn yellow. Current citrus growers are treating this by applying  a wide range of pesticides to their tree several times a year to minimize the spread of HLB. It is hard to detect the symptoms because it may not show up for more than a year after the tree is infected. Monitoring practices can include yellow sticky cards to trap and detect adult psyllid, visual monitoring by examining new leaves where the adult psyllid lay eggs in new flush, and misting with a detergent solution to get the aphids off.

There is a new study where ACP, the citrus green bacterium effects the insect vector by changing inside the insect. During the infection, the pathogen affects the good part of the bacteria and alters the metabolism so it can spread the pathogen. The study reveals weak points in the transmission cycle that could yield high specific targets for control strategies that can be more effective and more environmentally friendly than using a lot of pesticides (PLOS ONE papers).

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