Novel Symbiotic Association Between Euwallacea Ambrosia Beetle and Fusarium Fungus on Fig Trees in Japan

Abstract

Ficus carica plantations in Japan were first reported to be infested by an ambrosia beetle species, identified as Euwallacea interjectus, in 1996. The purpose of this study was to determine the symbiotic fungi of female adults of E. interjectus emerging from F. carica trees infected with fig wilt disease (FWD). Dispersal adults (51 females) of E. interjectus, which were collected from logs of an infested fig tree in Hiroshima Prefecture, Western Japan, were separated into three respective body parts (head, thorax, and abdomen) and used for fungal isolation. Isolated fungi were identified based on the morphological characteristics and DNA sequence data. Over 13 species of associated fungi were detected, of which a specific fungus, Fusarium kuroshium, was dominant in female head (including oral mycangia). The plant-pathogenic fungus of FWD, Ceratocystis ficicola, was not observed within any body parts of E. interjectus. We further discussed the relationship among E. interjectus and its associated fungi in fig tree.

Fungal Flora in Adult Females of the Rearing Population of Ambrosia Beetle Euwallacea interjectus (Blandford) (Coleoptera: Curculionidae: Scolytinae): Does It Differ from the Wild Population?

“…Our findings can be used to predict the adaptive capabilities of fungal symbionts in various growing conditions [51]. Additional information relating to the internal temperatures of preferred host trees of E. interjectus, such as fig, poplar, and [34] and reared ((b): 54 beetles) populations (Table 1). Numbers of beetles from which each fungal species was isolated is shown in pie charts.…”

“…In the wild population, which was collected from fig trees in the Hiroshima prefecture, F. kuroshium was closely associated with the adult E. interjectus female and was the most dominant in the head, including the oral mycangia [34]. In the reared population, Fusarium sp., which is distinct from F. kuroshium, was isolated from the adults.…”

“…The surface structure of the abdomen (elytra) may accidentally trap fungal spores, which can then be transported to the fig trees. [34] and reared ((b): 54 beetles) populations (Table 1). Numbers of beetles from which each fungal species was isolated is shown in pie charts.…”

“…Recently, we reported that the mycangia of E. interjectus were located in the oral cavity [33], and Fusarium kuroshium (Na, Carrillo et Eskalen ex Sand.-Den. et Crous) (Hypocreales: Nectriaceae) was closely associated with the wild adult female of E. interjectus [34]. However, the symbiont of E. interjectus grown in a rearing system established using the method of Mizuno and Kajimura [17] has not been evaluated.…”

“…We aimed to evaluate the fungal community in mycangia of reared E. interjectus compared to its wild population [34] to obtain a better understanding of beetle-fungus symbiosis and obtain useful information on the wilt disease of host trees. Towards this end, fungal species were isolated and identified in the head, thorax, and abdomen of female adults that were administered an artificial diet.…”