Curculionid beetles are significant pests of avocado trees (Persea americana [Lauraceae]). Adults of Heilus freyreissi (Coleoptera: Curculionidae) are reported for the first time on avocado trees, feeding on the tender lateral branches, the central leaf vein, inflorescences, peduncles, and fruits at the beginning of development. These injuries were consistently associated with symptoms of anthracnose disease caused by the fungus Colletotrichum sp. Thus, infestation of this insect may be of great economic significance in avocado production, because of its ability to attack various plant organs as well as it being a vector of the pathogen Colletotrichum sp.
Curculionid beetles are pests of many agricultural crops, including avocado Persea americana Miller (Lauraceae), which can be attacked by several species of Curculionidae such as Heilipus spp. (Vanin & Bená 2015), Euwallacea sp. (O'Donnell et al. 2016), Xyleborus glabratus Eichoff (Carrillo et al. 2012), and Conotrachelus perseae Barber (Castañeda-Vildózola et al. 2015).
The curculionid genus Heilus is represented by 18 species, 4 occurring in Central America and 14 in South America (O'Brien & Wibmer 1982). In Brazil, 11 species are reported, which are distributed throughout all states (Wibmer & O'Brien 1986; CTFB 2017; Splink 2017). To date, the genus Heilus has not been reported to cause economic damage to avocado production, and little is known about its hosts and interactions with pathogens.
Here, we report the first recorded occurrence of Heilus freyreissi Boheman (Coleoptera: Curculionidae) on avocado. Research on the presence of a new species of Heilus feeding on avocado would aid in the development of control strategies and provide basic information on this species.
Adults of the species H. freyreissi were found in 3 avocado orchards in the municipality of Rio Paranaíba, state of Minas Gerais, Brazil, in Oct 2016. The first orchard was located at 19.4358°S, 46.2836°W (1,176 masl) and was planted in 2004. The planting had an area of 18 ha and was planted with ‘Margarida' cultivar with a spacing of 8 m between rows and 6 m between plants. The 2nd orchard was located at 19.4355°S, 46.2858°W (1,176 masl) and was planted in 2004. The planting had an area of 12 ha and was planted with ‘Breda' cultivar, with 8 m spacing between rows and 6 m between plants. The 3rd orchard was located at 19.4122°S, 46.2662°W (1,176 masl) and was planted in 2005. The planting had an area of 15 ha and was planted with cultivar ‘Hass' at a spacing of 9 m between rows and 6 m between plants.
The climate of the region is a semi-humid tropical zone with an average annual temperature of 22 °C. The average annual rainfall is 1,500 mm per year, with 2 well-defined seasons: 1 cold and dry (Apr to Sep), and the other hot and rainy (Oct to Mar (Alvares et al. 2013).
For this study, 33 avocado fruits and branches were evaluated in 3 orchards, and the number of fruits and branches with Heilus spp. were counted. In the Margarida cultivar, 76% of branches and fruits had injury, while in the Breda and Hass cultivars, the injury was 100%.
Adult specimens (13 males and 3 females) were collected, stored in a 13 mL vial containing 70% v/v ethyl alcohol, and sent to Dr. Marinez Isaac Marques, Dr. Wesley Oliveira de Sousa, and Aline de Oliveira Lira for identification. The identified specimens were deposited in the Fr. J. S. Moure entomology collection at the Department of Zoology, Federal University of Paraná.
Adult H. freyreissi (Fig. 1A) were found commonly in clusters under the bark of avocado tree trunks (Fig. 1C). The pest was observed to attack young, tender, lateral branches (Fig. 1B), the central leaf veins, inflorescences, peduncles, and fruits at the beginning of development (Fig. 2). Lesions in the lateral branches were concentrated at the apex (20 cm from the end) and consisted of an elongated superficial scraping, ranging from 10 to 170 mm (Fig. 2A, B). Fruit injuries were 5 mm in diameter, concentrated in the pericarp (shell) and in the initial portion of the mesocarp (pulp), while no attacks on seeds were observed. Oxidation of perseitol, a 7-carbon alcohol compound released from the injured areas of avocado, resulted in the formation of a white exudate of solid consistency (Fig. 2F) (Hoddle & Hoddle 2008). The attack of the floral peduncle in the inflorescences resulted in injury similar to that on the branches, causing the flowers to fall (Fig. 2D).
For comparison of the injuries inflicted by H. freyreissi, the adults were collected in the field and packed in plastic trays containing plant organs without injury. After 3 d, the injuries to the avocado plant organs in the plastic trays were observed to be similar to those in the field. This comparison was made to verify that the injuries were indeed caused by H. freyreissi because similar injuries are caused by other curculionid species as well (Lourenção et al. 1984; Lourenção et al. 2003).
An important observation to note is that the injuries occurring on branches, inflorescences, and young fruits were consistently associated with symptoms of anthracnose disease caused by the fungus Colletotrichum sp. (Silva-Rojas & Ávila-Quezada 2011). The attacks on fruits often resulted in fruit drop. Healed lesions on avocados could affect its commercial value, especially that of varieties cultivated for export, because it is considered a defect in fruit quality.
Fig. 1.
Adult Heilus freyreissi isolated (A, B) and aggregated under the bark of the trunk of an avocado (C). The white ellipse indicates the location of the aggregation of adult beetles.
Insects that are associated with disease transmission in plants require greater attention in terms of their presence and management. Important crops can be attacked by curculionid beetles, which are vectors for disease. Rhynchophorus palmarum L. (Coleoptera: Curculionidae) attacks Palmaceae plants and transmits red ring disease of the coconut tree caused by the nematode Bursaphelenchus cocophilus Cobb (Nematoda: Aphelenchida: Parasitaphelenchidae) (Giblin-Davis et al. 2013). Similarly, banana crops (Musa spp. [Musaceae]) may be attacked by Cosmopolites sordidus Germar (Coleoptera:Curculionidae), a potential vector for the fungus Fusarium oxysporum Schlechtendahl (Nectriaceae) (Meldrum et al. 2013). In the case of avocado trees, several species of coleopterans can transmit the fungus Raffaelea lauricola T. C. Harr., (Ascomycota: Ophiostomataceae), which causes laurel wilt disease (Ploetz et al. 2017). A key point to be highlighted is that H. freyreissi attacks various avocado plant organs. Therefore, the injuries can occur at various stages of the crop development cycle, highlighting the necessity for crop management throughout the year.
To our knowledge, this is the first report of H. freyreissi as an avocado tree pest. Here, we describe the injuries caused by H. freyreissi to different plant organs and its association with the pathogen Colletotrichum sp., thus highlighting the potential of this insect to negatively affect avocado production.
We acknowledge Dr. Marinez Isaac Marques, Dr. Wesley Oliveira de Sousa, and Aline de Oliveira Lira for identification of the species. We thank the Tsuge Farm for the partnership and support in the development of this work. Funding was provided by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG).
