Using phylogenetic analysis to predict habits and host plant use trends in Heilipus species

The genus Heilipus is a tropical lineage comprising 90 described species, with its greatest diversity found in the Neotropical region. Among them, some species are known to bore into seeds or trunks during their larval stage. To date, the habits and host plants of only 24 species are documented: 12 seed borers (spermophagous species) associated exclusively with plants of the family Lauraceae, and 12 trunk borers, nine associated with Lauraceae and the remaining three with trunks of the genus Annona L. (family Annonaceae). 

A recent study on Heilipus host plants suggests that seed-boring is a more specialized habit, restricted to Lauraceae, while trunk-boring appears more generalist, having been recorded in both Lauraceae and Annonaceae. The same study also identified a strong ecological association between Heilipus and Lauraceae: of the 38 plant species documented as hosts, 33 belong to this family. In spermophagous species, this association is so tight that Heilipus has been proposed as one of the most important groups of pre-dispersal seed predators of Lauraceae in the Americas.

Although the close ecological association between Heilipus and the family Lauraceae is now well established, with evidence of coevolution in some cases, the genus has traditionally been recognized for the damage that certain species inflict on avocado crops (Persea americana Mill.). This impact has positioned Heilipus as a genus of agricultural relevance and kept it under scrutiny within avocado production systems. Of the 90 species, 10 have been reported to cause damage to avocado: three seed borers and seven trunk and branch borers. The first documented seed borer was H. lauri Boheman, described from a specimen collected in Mexico and currently listed as a quarantine pest by the United States. The larval behavior of H. pittieri Barber and H. trifasciatus (Fabricius), the other two species known to bore avocado seeds, was documented later, in 1919 and 1920, respectively. Since those reports, no additional Heilipus species have been recorded as seed borers in avocado.

In contrast, the number of trunk-boring Heilipus species reported in avocado crops has been steadily increasing since H. catagraphus Germar was first documented in Brazil in 1915. As avocado cultivation gained popularity and expanded across the Americas, the presence of trunk borers rose gradually: from two species reported in the first half of the 20th century to seven by 2024. This sustained increase is likely driven by the loss of native host plants due to the expansion of avocado plantations, which has forced Heilipus species to seek alternative hosts. Given the genus's close ecological association with the family Lauraceae, avocado serves as a suitable confamilial host, offering high-quality, concentrated resources in monoculture systems.

Could additional Heilipus species, beyond the seven already reported, be found boring into avocado trunks in the near future? Very likely. Conversely, it is less likely that other Heilipus species will colonize avocado seeds, as these tissues are more chemically defended than trunks and involve much more specialized ecological interactions.

Which species, then, could eventually appear –or be expected– in avocado crops? A phylogenetic analysis based on anatomical characters, derived from one of the chapters of my dissertation, recovered a clade of 11 species (the H. catagraphus–H. championi clade), four of which have already been reported as avocado trunk borers in the Americas: H. albopictus (Champion) in Mexico, H. catagraphus Germar in Brazil, and H. elegans Guérin and H. leopardus Boheman in Colombia. 

The remaining seven species in the clade are likely trunk borers of Lauraceae and may eventually be detected in avocado crops, as it occurred with the four previously mentioned. Notably, five of these species are distributed in countries that lead global avocado production and export: H. cruciatus Chevrolat (Fig.) and H. fenestratus (Champion) (Fig.) in Mexico, and H. commodus (Pascoe) (Fig.), H. fryi (Pascoe) (Fig.), and H. poecilus (Pascoe) in Peru. It is therefore important to monitor the presence of these species in avocado-growing regions of the countries listed, as well as in neighboring ones.

The phylogenetic analysis not only enabled the identification of Heilipus species that may soon be found as avocado trunk borers, but also others that are likely spermophagous, whose habits remain undocumented. This is the case of H. clathratus (Champion) (Fig.) and H. limbatus (Champion) (Fig.), two species distributed in Panama that probably bore seeds during their larval stage. The analysis even made it possible to predict which plant lineages these species might be associated with. 

For instance, H. limbatus is possibly associated with seeds of the Cinnamomeae clade within the family Lauraceae, based on anatomical characters shared with H. draco (Fabricius) and H. guttiger (Champion), two species recorded in several genera of that plant lineage. Heilipus clathratus, on the other hand, may be associated with seeds of the genus Persea, as it shares characters with the three avocado seed borers reported to date. It should be noted that this association may not necessarily involve Persea americana, but may instead concern other members of the genus.

These findings highlight the predictive value of phylogenetic studies in identifying trends in host plant use and potential colonization of new areas. Moreover, they are useful for anticipating the emergence of new pests and supporting the development of proactive management strategies. A summary of this phylogenetic analysis is available here.

Future efforts will focus on expanding the phylogenetic analysis with additional anatomical characters and broadening the selection of outgroups. This will enable the testing of evolutionary hypotheses regarding the early divergence of trunk borers from seed borers, while also continuing to infer the potential habits of species whose biology remains unknown. Ultimately, the aim is to deepen our understanding of the natural and evolutionary history of Heilipus, a genus that transcends avocado and is intricately linked to the family Lauraceae. So close is this association that we might well refer to them as “the laurel weevils”.

Acknowledgements

I am grateful to Dr. Jennifer Girón, coauthor of the phylogenetic analysis, for her guidance. I also thank the institutions that funded this work: the Secretaría de Ciencia, Humanidades, Tecnología e Innovación de México (Secihti), The Coleopterists Society, and The Smithsonian Institution.