The relationship between the wood‐boring pest Anoplophora glabripennis and pathogen Fusarium solani in the native range

Wood-feeding insects often rely on microbial symbionts to thrive on nutrient-poor xylem. Anoplophora glabripennis is a wood-boring pest that inhabits a wide range of healthy deciduous hosts. The fungus Fusarium solani is associated with A. glabripennis. This study investigated their relationship in the native range of A. glabripennis, and evaluated how F. solani is carried and transmitted, as well as the phylogenetic relationship of F. solani species complex (FSSC) populations from different countries. Fungal communities differed among eggs carried by adult, oviposition secretions, healthy phloem adjacent to the oviposition pit, and soft rot phloem consumed by newly hatched larvae; but were similar in eggs and secretions. F. solani was highly enriched in eggs (93.07%), oviposition secretions (86.39%), and soft rot phloem (63.44%), but was absent in healthy phloem. The F. solani isolation rate from oviposition pits was 100% across different hosts and locations, and it was found in larval guts and frass at all life stages. In addition, GFP-labeled F. solani was only detected in larval guts (10, 40, 60 days post-feeding), but not in the fat body or epidermal tissue. Newly hatched larvae had the highest FSSC-specific copy numbers in their guts than those at other life stages. FSSC isolated from the gut of A. glabripennis in China forms a separate clade, with a relatively distant genetic relationship to the United States larval isolates. These results support the symbiotic relationship between A. glabripennis and F. solani, and demonstrate that F. solani is transmitted via female adult oviposition and carried in the guts by larval feeding.