Diversity and virulence of the fungus Beauveria (Cordycipitaceae) species associated with Gonipterus sp. n. 2 (Coleoptera: Curculionidae) in South Africa

Abstract

In South African forestry, the Eucalyptus snout beetle, Gonipterus sp. n. 2 (Coleoptera: Curculionidae), has become an economically important invasive pest. The adults and larvae feed on leaves and cause severe damage to Eucalyptus plantations. The egg parasitoid, Anaphes nitens Girault (Hymenoptera: Mymaridae) was introduced to control Gonipterus sp. n. 2 populations, but additional biological control is necessary. Entomopathogenic fungi (EPF) can potentially be used effectively together with A. nitens, as they can target different life stages. Entomopathogenic fungi are able to infect host insects by direct contact to the insect cuticle, killing the host and sporulating on the dead insect to infect unsuspecting healthy hosts. This study focussed on the Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) species associated with Gonipterus sp. n. 2, as well as their virulence towards adult beetles. The study found that B. bassiana cryptic species diversity was present in South Africa and associated with Gonipterus sp. n. 2. The newly described species, B. namnaoensis, as well as two novel species, Beauveria sp. nov. 1 and Beauveria sp. nov. 2 formed part of the B. bassiana cryptic species complex. Beauveria pseudobassiana species were also obtained from Gonipterus sp. n. 2 cadavers. The virulence of these species was analysed in virulence trials. Inter- and intraspecies variation in virulence were observed during the trials. The most virulent strains with the lowest survival of beetles belonged to B. namnaoensis and Beauveria sp. nov. 1. The least virulent strains with the highest beetle survivals recorded were that of two Beauveria sp. nov. 2 strains and one B. pseudobassiana strain. Moderate virulence and survival were attributed to one B. bassiana, B. pseudobassiana and two remaining Beauveria sp. nov. 2 strains. Thus, the most virulent strains of the newly described species, B. namnaoensis, as well as Beauveria sp. nov. 1 and Beauveria sp. nov. 2 could be considered for Gonipterus sp. n. 2 biological control in South African forestry.