Phylogeny and biological control of weevils (Curculionidae) in the Western Cape Province

The genus Phlyctinus contains cryptic diversity, and two pest species, Phlyctinus callosus and Phlyctinus xerophilus. As the two species may differ in susceptibility to entomopathogens, bioassays of appropriate biocontrol agents need to be conducted on larvae, pupae and adults of both species; including ecologically relevant trials.

Phlylogenetic and species boundary delimitation assessments of 5 single genes on all known lineages of the genus Phlyctinus.

Laboratory screenings of the entomopathogenic nematode (EPN) Steinernema yirgalemense on larvae and pupae of P. callosus and P. xerophilus.

In-field screening of S. yirgalemense against buried P. callosus and P. xerophilus larvae.

Ecologically relevant bioassay in laboratory cages of the entomopathogenic fungus (EPF) product Broadband^® on adult P. callosus and P. xerophilus.

The genus Phlyctinus contains approximately 8 species, based on analysis of single gene regions (Hévin et al., 2022). Only the two species Phlyctinus callosus and Phlyctinus xerophilus contain lineages of agricultural significance, and neither species constitute an emerging pest (Hansen et al., 2024a).

Larval P. callosus and P. xerophilus are equally susceptible to S. yirgalemense under lab conditions. Pupae are approximately 2-4 times more susceptible to S. yirgalemense than larvae. Under field conditions, P. xerophilus larvae appear to be more susceptible to S. yirgalemense than P. callosus larvae, with approximately 22% and 45% control being achieved for P. callosus and P. xerophilus larvae respectively after 96 hour of exposure (Hansen et al., 2024b).

Treatment with Broadband^® generally does not cause statistically faster or higher mortality on Phlyctinus adults than a control treatment in ecologically relevant bioassays.

Approximately 8 species of Phlyctinus weevil occur naturally in the South Western Cape province. Only certain lineages of the two species, Phlyctinus callosus sensu stricto, and Phlyctinus xerophilus, are economically significant pests of agriculture. Neither of these species are emerging pests, and trunk exclusion barriers will function equally well against both species.

The EPN S. yirgalemense has potential to be used as a biological control agent of P. callosus and P. xerophilus targeting larvae and pupae. Broadband appears to be an ineffective biological control product in targeting adult Phlyctinus, in spite of promising virulence shown in virulence screenings.