Among leafhoppers (Hemiptera, Cicadellidae), only Typhlocybinae are known in Mexico to inhabit avocado, an important horticultural crop. In this paper, a potential avocado pest, Dikrella mella Ruppel & DeLong, 1952, is redescribed and illustrated. Additionally, a detailed checklist and a key for all known species of Typhlocybinae associated with avocado trees in Mexico are provided.

Alconeura, Auchenorrhyncha, Empoasca, Empoascini, Idona, Joruma, Typhlocybinae

Herbivorous sap-sucking insects are potentially devastating agricultural pests because they not only injure plants directly but may also transmit plant pathogens (Bosco and Marzachi 2016). Most such pests belong to the order Hemiptera (Hogenhout et al. 2008), of which the family Cicadellidae (leafhoppers) (Hemiptera: Auchenorrhyncha) is the most relevant because it comprises around 75% of plant pathogen vector species (Weintraub and Beanland 2006). Within leafhoppers, the subfamily Typhlocybinae is reported to spread several kinds of pathogens effectively due to their high capacity for dispersal. Leafhopper vectors often go unnoticed when transmitting plant diseases, their presence only being detected after disease outbreaks occur (Nault 1979).

Avocado is one of the most important horticultural crops worldwide and Mexico is the main exporter (SAGARPA 2017). Recently five species of leafhoppers were identified as being associated with avocado trees in central Mexico (Quezada-Daniel et al. 2017). All of those species belong to the subfamily Typhlocybinae. Our study of leafhoppers from several entomological collections in Mexico revealed that these species have been widely misidentified. For example, specimens of Dikrella mella Ruppel & DeLong, 1952, housed in Mexican collections were often misidentified as Empoasca spp., presumably based on superficial resemblance in size and coloration.

The genus Dikrella Oman, 1949 was described based on type-species Dikraneura cockerellii Gillette, 1895. Oman (1949) also moved 14 species previously placed in Dikraneura Hardy, 1850 to Dikrella. Today, the genus includes two subgenera: Readionia Young, 1952 with four species and Dikrella Oman, 1949 with 37 well-defined species and three subspecies. The genus is restricted to the New World. Only one species of the genus is known so far to be a potential vector of diseases of avocado crops.

Dikrella mella Ruppel & DeLong, 1952 was described from four localities in Mexico based on two males and four females. The original description and illustrations lack important details useful for distinguishing the species. Since then, no further information was published on its distribution or host plants. Here we provide a redescription and diagnostic illustrations of this important avocado leafhopper. We also provide a detailed checklist and a key to all known species recorded from avocado trees in Mexico.

All specimens identified in this study are housed at the Colección Nacional de Insectos, Instituto de Biología, Universidad Nacional Autónoma de México, Mexico (CNIN), Colección de Insectos del Instituto de Fitosanidad, Colegio de Postgraduados, Texcoco, Estado de México, Mexico (CEAM), Colección de Auchenorrhyncha de Jorge Adilson Pinedo Escatel, Mexico (CAJAPE), Colección Entomológica del Centro de Estudios en Zoología, Universidad de Guadalajara, Zapopan, Mexico (CZUG), and C.A. Triplehorn Insect Collection, Ohio State University, Columbus, USA (OSUC).

Taxonomic criteria and terminology follows mainly Young (1952), Dietrich (2005), and Dmitriev (2010). Techniques for preparation of male genital structures follow Oman (1949) modified such that male abdomens were rinsed with water mixed with alcohol at different concentrations. Label data are given between quotation marks, with a backslash (\) separating the lines on the labels. Images of habitus were taken using a Carl Zeiss camera mounted on a Stemi 2000c stereo-microscope, and illustrations were drawn using a camera lucida attached to a Leica stereo microscope. Subsequently, drawings were digitized and vectorized with Adobe Illustrator and edited in Adobe Photoshop. Measurements were obtained using an electronic vernier.

Nine species in five genera of typhlocybine leafhoppers are reported from avocado trees in Mexico. None of these species have been tested or confirmed to transmit any disease so far. Species are recorded from Mexican states (Table 1), of which Morelos is the best sampled and is home to seven species. Additional sampling is underway for the purpose of management and monitoring in states with high levels of avocado production within Mexico and will undoubtedly provide additional avocado-associated records.

The first author is very grateful to Axel Cristobal P. E. for comments during development of manuscript. We kindly were helped by Christopher Dietrich (Illinois Natural History Survey. USA) and Maria I. Catalano (Centro de Bioinvestigaciones de la Universidad Nacional del Noroeste de la provincia de Buenos Aires) with helpful comments to improve the manuscript. Edith Blanco-Rodríguez helped corroborate identification of the specimens. We also thank curators of collections, Luciana Musetti (OSUC), Harry Brailovsky and M. Cristina Mayorga-Martínez (CNIN), Jose Luis Navarrete-Heredia (CZUG), and Jesus Romero-Nápoles (CEAM) for access to types and other specimens. J.A. Pinedo-Escatel is supported by CONACyT [CVU: 705854] and BEMARENA Ph.D. program of the Universidad de Guadalajara at Centro Universitario de Ciencias Biológicas y Agropecuarias, Zapopan, Jalisco, Mexico. Dmitry Dmitriev is supported by National Science Foundation [NSF 16-39601].