| Summary: | Ricin-B-lectins (RBLs) have been identified in many groups of organisms, including coleopterans insects, particularly the Colorado potato beetle <i>Leptinotarsa decemlineata</i> (LdRBLs). We hypothesized that one of these LdRBLs (LdRBLk) may be involved in the immune response to fungal infections. We performed a theoretical analysis of the structure of this protein. Additionally, the expression levels of the <i>LdRBlk</i> gene were measured in <i>L. decemlineata</i> in response to infections with the fungi <i>Metarhizium robertsii</i> and <i>Beauveria bassiana</i>. The expression levels of <i>LdRBlk</i> in the <i>L. decemlineata</i> cuticle and fat body were increased in response to both infections. The induction of <i>LdRBlk</i> expression was dependent on the susceptibility of larvae to the fungi. Upregulation of the <i>LdRBlk</i> gene was also observed in response to other stresses, particularly thermal burns. Elevation of <i>LdRBlk</i> expression was frequently observed to be correlated with the expression of the antimicrobial peptide <i>attacin</i> but was not correlated with <i>hsp90</i> regulation. Commercially available β-lectin of ricin from <i>Ricinus</i><i>communis</i> was observed to inhibit the germination of conidia of the fungi. We suggest that LdRBLk is involved in antifungal immune responses in the Colorado potato beetle, either exerting fungicidal properties directly or acting as a modulator of the immune response.
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