Virus-based vectors have been used as laboratory tools for short term
experiments on herbaceous plants. They are stable enough to be used for
introducing foreign genes to plants. However, the development of stable
vectors has now showed potential use in perennial plants.

Citrus tristeza virus (CTV), a stable virus-based vector, is being
considered for use in the control of Huanglongbing (HLB). Huanglongbing,
also known as Citrus Greening disease, is caused by the bacteria Candidatus
Liberibacter asiaticus (CLas). Although there are no known effective control
for CLas, the CTV vector aims to control HLB by controlling its vector, the
Asian citrus psyllid (Diaphorina citri). This insect targets the plants'
phloem, which is also where both CLas and CTV thrive in the plant. This is
exploited to develop a method to control HLB through RNA interference
(RNAi).

CTV-RNAi vector with the abnormal wing disc (Awd) gene of D. citri, induces
an altered Awd gene expression when ingested by the insects' nymphs. The
altered expression silences the Awd gene which results in malformed-wing
phenotype in adults and increased adult mortality. This impaired ability
potentially limits the successful vectoring of CLas bacteria between citrus
trees.

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