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During a survey in Trinidad and Grenada for putative vectors of palm lethal decline phytoplasmas, three species of planthopper in the genus Melanoliarus (Hemiptera, Cixiidae) were collected. Melanoliarus maidis was collected from coconut palms in Grenada, M. kindli was collected from grasses in a coconut plot in Trinidad and a new species of Melanoliarus was collected from coconut palms in Trinidad. Herein the novel taxon is described with supplementary molecular data for the cytochrome c oxidase subunit I (COI) gene, 18S rRNA gene, and histone 3 (H3) gene to support placement in the genus Melanoliarus in the strict sense.

Haplaxius is a large genus of cixiid planthopper found in the New World. The genus is of particular interest due to the ability of H. crudus to transmit the phytoplasmas for lethal decline in various palm species, primarily in the Caribbean and Florida, U.S.A. During recent vector survey work in Jamaica, a specimen was collected at Castleton Botanic Garden and determined to be a new species of Haplaxius. The novel taxon is herein described, Haplaxius fornicus sp. n., and corresponding DNA sequence data is provided for the barcoding region of the cytochrome c oxidase subunit I (COI) gene, 18S rRNA gene, and histone 3 (H3) gene. An updated phylogeny of the genus is provided with currently available taxa demonstrating additional support for the placement of H. fornicus sp. n. in Haplaxius.

“Huanglongbing” (HLB) is one of the most devastating diseases of citrus orchards worldwide. Samples from about 200 citrus plants of different cultivars and rootstock/cultivar combinations, showing HLB symptoms in Cuba, Jamaica and Guadeloupe-France, were tested to verify the possible presence of 'Candidatus Phytoplasma' in 'Candidatus Liberibacter asiaticus' infected species. About the 14% of the samples infected with 'Ca. Liberibacter' were also found positive to phytoplasmas, indicating the presence of mixed infection especially in the orchards located in Cuba. Moreover, in one of the samples from Jamaica mixed phytoplasma infection was detected. Further, the detection of only phytoplasmas in several symptomatic citrus samples collected from Cuba and Guadeloupe, confirmed that the symptomatology cannot be the sole criterium to discriminate between the presence of the two pathogens, and molecular identification of the bacteria is necessary to verify the sanitary status of symptomatic plants. Diaphorina citri insects collected in Cuba and Guadeloupe resulted positive to the 'Ca. L. asiaticus' presence confirming its active role in the dissemination of the pathogen in the Caribbean areas. Only one insect of the Cicadidae family, collected in Guadeloupe, was found positive for phytoplasma presence. Phytoplasmas enclosed in groups 16SrI and 16SrXII were identified in all the three islands; the 16SrII, 16SrIV, 16SrVII, 16SrX and 16SrXI groups were present in both Guadeloupe and Cuba. This could indicate that the surrounding cultivated species are influencing the phytoplasma population composition in citrus orchards as indicated by the relevant presence of the lethal yellowing phytoplasmas that was severely affecting the Cuban palm plantations in the past. Moreover the identification of phytoplasmas enclosed in groups 16SrIII, 16SrVI and 16SrIX only in Guadeloupe and of 16SrXV group only in Cuba is corroborating this hypothesis (Bertaccini et al., 2019; Luis-Pantoja et al., 2021). Considering that diverse 'Candidatus Phytoplasma'-related species were detected in the three countries in different citrus varieties, a relevant role as phytoplasma reservoir can be attributed to citrus orchards for the natural and agricultural ecosystems.

Descriptions of lethal yellowing (LY) in coconut plants were documented in the late 19th century in the Caribbean region, but the first widespread devastation of coconuts due to LY took place in Jamaica during the 1960s. Subsequently, reports of LY began to emerge in other countries such as the USA (Florida), Mexico, Belize, Honduras, Guatemala, and various other Caribbean islands including Bahamas, Cayman Islands, Cuba, Haiti, Dominican Republic and St. Kitts and Nevis in the Leeward Island, Antigua and Barbuda and St. Maarten. Similar diseases known collectively as lethal yellowing-type syndromes have also been described elsewhere in the tropics. In West Africa: Awka wilt in Nigeria, Cape St. Paul wilt in Ghana and Ivory Coast, Kaïncopé in Togo, and Kribi in Cameroon. In East Africa, a lethal disease also occurs in Kenya, Tanzania and Mozambique. Bogia syndrome in Papua New Guinea and Solomon Islands and a lethal wilt in Australia have been described. In spite of the different names the disease symptoms are very similar, while the associated phytoplasmas are diverse in the various geographic areas. Five 'Candidatus Phytoplasma' species are reported as associated with lethal yellowing syndromes in palms in the diverse continents: 'Ca. P. palmicola' and 'Ca. P. cocostanzaniae' in Africa, 'Ca. P. palmae' in America, 'Ca. noviguineense' and 'Ca. P. dypsidis' in Papua New Guinea and Australia. Other non-lethal yellowing phytoplasma-associated diseases are described in coconut in south and south-east Asia, such as Weligama wilt in Sri Lanka and Kerala wilt in India, and in different palm species such as oil palm, date palm and arecanut palm in Colombia, Indian subcontinent, Saudi Arabia and Kuwait where 'Ca. P. asteris', 'Ca. P. oryzae', 'Ca. P. wodyetiae' and 'Ca. P. cynodontis' were respectively reported (Yankey et al., 2018 ). Although the transmission of phytoplasmas to and among palms has been intensively studied, to date the only insect vector identified is Haplaxius crudus proved to transmit 'Ca. P. palmae' in America. For this phytoplasma the possibility of embryo transmission was also recently proved. For all the other reported lethal yellowing syndromes there is scattered information about possible insect vectors and some of these in both Africa and America have only recently been reported. The management of these diseases is mainly through integrated management approaches including monitoring to detect palms with early LY symptoms, elimination of these palms as soon as they are detected, replanting and weeding. Search for resistant varieties appears however the long lasting approach to be pursued together with the continuous monitoring of phytoplasma strains present in the diverse areas.