New data on an old pest complex: The status of Phlyctinus callosus Schönherr and Phlyctinus xerophilus Haran (Coleoptera: Curculionidae) in South Africa

Abstract

Phlyctinus is an endemic weevil genus of the Cape Floristic Region that comprises eight to ten species, previously classified under the monotypic P. callosus sensu lato concept. Two species of this genus, Phlyctinus callosus and P. xerophilus, are of economic concern to the deciduous fruit and grapevine industry in the Western Cape province of South Africa, causing primary damages and being of phytosanitary concern at the adult stage. The taxonomic revision conducted in 2020 raised doubts whether one of the two species was a newly emerging pest and/or what species was considered in studies before the clarification of species boundaries. Also unclear is whether these species can be controlled similarly using current control measures. The aim of this study therefore is to review the pest status of the two species over time based on museum records, field collections and historical publications, and to clarify how control measure(s) are impacted. We infer that neither species appear to be emerging pests in the region, both being of agricultural significance for at least 80 years. Phlyctinus callosus is mostly distributed along the southern coast, while P. xerophilus is distributed in inland valleys. The two species show similar biology, physiology and ecology in agro-ecosystems, and can be excluded from the host plant canopy using stem-barriers, adults being flightless. As such, it is shown that the naming of P. xerophilus as a pest is mainly a taxonomical clarification within a pre-existing species complex.