Abstract
African citrus psyllid (Trioza erytreae (Del Guercio)) is a vector insect of the bacterium Candidatus Liberibacter africanus, the putative causal agent of Huanglongbing, the most devastating citrus disease in the world. The insect was found on the island of Madeira in 1994 and in mainland Portugal in 2015. Present in the north and center of the country, it is a threat to Algarve, the main citrus-producing region. Trioza erytreae eggs and first instar nymphs are sensitive to the combination of high temperatures and low relative humidity. Daily maximum air temperature and minimum relative humidity data from 18 weather stations were used to calculate the water vapor pressure deficit (vpd) from 2004 to 2018 at various locations. Based on the mean vpd and the number of unfavorable days (vpd < 34.5 and vpd < 56 mbar) of two time periods (February to May and June to September), less favorable zones for T. erytreae were identified. The zones with thermal and water conditions like those observed in the Castelo Branco and Portalegre (Center), Beja (Alentejo), Alte, and Norinha (Algarve) stations showed climatic restrictions to the development of eggs and first instar nymphs of African citrus psyllid. Effective control measures, such as the introduction and mass release of Tamarixia dryi (Waterson), a specific parasitoid, and chemical control are necessary in favorable periods for T. erytreae development, such as in spring and in areas with limited or no climate restrictions.
Highlights
African citrus psyllid (Trioza erytreae (Del Guercio)) is a vector insect of the bacterium CandidatusLiberibacter africanus, the putative causal agent of Huanglongbing (HLB), known as Greening, which is the most devastating citrus disease in the world
The daily vapor pressure deficit according to the formula vpd = sp − ap, where saturation pressure was
The second period, from June to October, included the summer months and September, covering the later flush. These two periods covered the full span of when the trees had the young leaves necessary for egg laying and the development of immature T. erytreae
Summary
African citrus psyllid (Trioza erytreae (Del Guercio)) is a vector insect of the bacterium Candidatus. Liberibacter africanus, the putative causal agent of Huanglongbing (HLB), known as Greening, which is the most devastating citrus disease in the world. This species was discovered on the island of Insects 2020, 11, 229; doi:10.3390/insects11040229 www.mdpi.com/journal/insects. The bacteria associated with HLB have not been found in Europe, but the presence of the insect vector makes an eventual accidental introduction of the bacteria a looming disaster for European citrus production. The African HLB pathosystem (HLBaf) associated with the bacterium Candidatus Liberibacter africanus (CLaf) transmitted by T. erytreae is climate-dependent and is intolerant to high temperatures [5,6]
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