Secretion and Detection of Defensive Compounds by the Red Flour Beetle Tribolium castaneum Interacting with the Insect Pathogenic Fungus Beauveria bassiana

Abstract

Entomopathogenic fungi such as Beauveria bassiana are extensively used for the control of insect pests worldwide. They infect mostly by adhesion to the insect surface and penetration through the cuticle. However, some insects, such as the red flour beetle Tribolium castaneum (Herbst), have evolved resistance by embedding their cuticle with antifungal compounds. Thus, they avoid fungal germination on the cuticle, which result in low susceptibility to entomopathogenic fungi. In adult T. castaneum, these antifungals are the well-known defensive compounds methyl-1,4- and ethyl-1,4-benzoquinone. In this study, we added B. bassiana conidia on the diet of adult beetles to study the effect of the entomopathogen on the secretion and detection of the beetle volatile blend containing both benzoquinones. The compounds were analyzed by solid phase microextraction coupled to gas chromatography–flame ionization detection, and were detected by electroantennography. In addition, we measured the expression level of four genes encoding for two odorant-binding proteins (OBP), one chemosensory protein (CSP), and one odorant receptor (OR) in both healthy and fungus-treated insects. Significant alterations in the secretion of both benzoquinones, as well as in the perception of methyl-1,4-benzoquinone, were found in fungus-treated insects. TcOBP7D, TcOBP0A and TcCSP3A genes were down-regulated in insects fed conidia for 12 and 48 h, and the latter gene was up-regulated in 72 h samples. TcOR1 expression was not altered at the feeding times studied. We conclude that fungus-treated insects alter both secretion and perception of benzoquinones, but additional functional and genetic studies are needed to fully understand the effects of fungal infection on the insect chemical ecology.

The Potential of Two Entomopathogenic Fungi and Enhanced Diatomaceous Earth Mixed with Abamectin: A Comprehensive Study on Mortality, Progeny Production, Application Method, and Surface Application against Tribolium castaneum

“…Beauveria bassiana [50][51][52][53] and M. anisopliae [54][55][56] have been extensively investigated for their effectiveness in controlling T. castaneum. However, the repeated use of entomopathogenic fungi can lead to the development of resistance in T. castaneum populations [57,58]. This phenomenon can be explained by the hypothesis of the Red Queen, which proposes that for evolutionary purposes, the host must continuously adapt to defend against its natural enemies [59].…”

The Endogenous Metabolic Response of Tribolium castaneum under a High Concentration of CO2

“…In addition, nonchemical pest control methods, including low storage temperatures and entomopathogenic fungi, can also prevent the development of stored product pests [10,11]. However, this insect has already shown capacities for developing insecticide resistance, even to the entomopathogenic fungus Beauveria bassiana (Balsamo) [11][12][13][14][15]. Therefore, the development of more specific and less environmentally harmful control methods is particularly urgent to tackle this widespread insect pest.…”