Alkane-priming of Beauveria bassiana strains to improve biocontrol of the redbanded stink bug Piezodorus guildinii and the bronze bug Thaumastocoris peregrinus

Abstract

Insect epicuticle hydrocarbons (CHC) are known to be important determinants in the susceptibility degree of insects to fungal entomopathogens. Five Beauveria bassiana (Balsamo) Vuillemin (Hypocreales; Clavicipitaceae) strains were phenotypically analyzed regarding their response to CHC nutrition and their pathogenicity and virulence towards high fungal-susceptible Thaumastocoris peregrinus (Carpintero and Dellapé) (Heteroptera: Thaumastocoridae) and low fungal-susceptible Piezodorus guildinii (Westwood) (Hemiptera: Pentatomidae), which are important hemipteran pests in eucalyptus and soybean plantations, respectively. Two of these strains, which were the most (ILB308) and the least (ILB299) virulent to P. guildinii, were also evaluated at gene expression level after growth on n-pentadecane, a P. guildinii epicuticular hydrocarbon. Beauveria bassiana hypervirulent strain ILB308 showed the lowest growth on most evaluated CHC media. However, this strain distinctively induced most of the analyzed genes involved in CHC assimilation, cuticle degradation and stress tolerance. Virulence towards low susceptibility P. guildinii was enhanced in both hypervirulent ILB308 and hypovirulent ILB299 strains after growth on n-pentadecane as the sole carbon source, whereas virulence enhancement towards high susceptibility T. peregrinus was only observed in the hypervirulent strain. Virulence enhancement towards P. guildinii could be mostly explained by a priming effect produced by CHC on the induction of some genes related to hydrocarbon assimilation in ILB299 and ILB308, such as cytochrome P450 genes (BbCyp52g11 and BbCyp52x1), together with adhesion and stress tolerance genes, such as hydrophobin (Bbhyd2) and catalase (Bbcatc) and glutathione peroxidase (Bbgpx), respectively.