Dietary potential of the symbiotic fungus for the larvae of a nonsocial fungus-cultivating weevil .

Unlabelled: Many insect taxa cultivate fungi for food. Compared to well-known fungus cultivation in social insects, our knowledge on fungus cultivation in nonsocial insects is still limited. Here, we studied the nutritional potentials of the fungal cultivar, , for the larvae of its nonsocial insect farmer, , a specialist on Japanese knotweed . Overall, fungal hyphae and leaf rolls contained significantly higher carbon (C), stable isotopes of C (δC), and nitrogen (δN) but significantly lower C/N ratios compared to unrolled leaves, whereas insect bodies contained significantly higher N contents but lower C and C/N ratios compared to other types of samples. The MixSIAR model indicated that fungal hyphae contributed a larger proportion (0.626-0.797) to the diet of larvae than leaf materials. The levels of ergosterol, six essential amino acids, seven nonessential amino acids, and three B vitamins tested in fungal hyphae and/or leaf rolls were significantly higher than in unrolled leaves and/or larvae. The genome contains the complete set of genes required for the biosynthesis of ergosterol, the essential amino acids valine and threonine, nine nonessential amino acids, and vitamins B2 and B3, whereas some genes associated with five essential and one nonessential amino acid were lost in the genome. These suggest that is capable of providing the larvae food with ergosterol, amino acids, and B vitamins. appears to be able to synthesize or concentrate these nutrients considering that they were specifically concentrated in fungal hyphae.

Importance: The cultivation of fungi for food has occurred across divergent insect lineages such as social ants, termites, and ambrosia beetles, as well as some seldom-reported solitary insects. Although the fungal cultivars of these insects have been studied for decades, the dietary potential of fungal cultivars for their hosts (especially for those nonsocial insects) is largely unknown. Our research on the mutualistic system - represents an example of the diverse nutritional potentials of the fungal cultivar in the diet of the larvae of its solitary host, . These results demonstrate that has the potential to synthesize or concentrate ergosterol, amino acids, and B vitamins and benefits the larvae of . Our findings would shed light on poorly understood fungal cultivation mutualisms in nonsocial insects and underscore the nutritional importance of fungal cultivars in fungal cultivation mutualisms.