The Ambrosia Symbiosis: From Evolutionary Ecology to Practical Management

Wood decay fungus Flavodon ambrosius (Basidiomycota: Polyporales) is widely farmed by two genera of ambrosia beetles

The ambrosia fungus Flavodon ambrosius is the primary nutritional mutualist of ambrosia beetles Ambrosiodmus and Ambrosiophilus in North America. F. ambrosius is the only known ambrosial basidiomycete, unique in its efficient lignocellulose degradation. F. ambrosius is associated with both native American beetle species and species introduced from Asia. It remains unknown whether F. ambrosius is strictly a North American fungus, or whether it is also associated with these ambrosia beetle genera on other continents. We isolated fungi from the mycangia and galleries of ambrosia beetles Ambrosiodmus rubricollis, Ambrosiodmus minor, Ambrosiophilus atratus, and Ambrosiophilus subnepotulus in China, South Korea, and Vietnam. Phylogenetic analyses suggest that all Asian and North American isolates represent a single haplotype. These results confirm Flavodon ambrosius as the exclusive mutualistic fungus of multiple Ambrosiodmus and Ambrosiophilus beetle species around the world, making it the most widespread known ambrosia fungus species, both geographically and in terms of the number of beetle species. The Flavodon-beetle symbiosis appears to employ an unusually strict mechanism for maintaining fidelity, compared to the symbioses of the related Xyleborini beetles, which mostly vector more dynamic fungal communities.

Attraction of the Euwallacea sp. near fornicatus (Coleoptera: Curculionidae) to Quercivorol and to Infestations in Avocado

The Euwallacea sp. near fornicatus (Euwallacea sp. 1 hereafter) feeds on many woody shrubs and trees and is a pest of avocado, Persea americana Mill., in several countries including Israel and the United States. Quercivorol baits are commercially available for Euwallacea sp. 1 females (males do not fly), but their attractive strength compared to other pheromones and potential for mass trapping are unknown. We used sticky traps baited with quercivorol released at 0.126 mg/d (1×) and at 0.01×, 0.1×, and 10× relative rates to obtain a dose-response curve of Euwallacea sp. 1 attraction. The curve fitted well a kinetic formation function of first order. Naturally infested limbs of living avocado trees had attraction rates equivalent to 1× quercivorol. An effective attraction radius (EAR) was calculated according to previous equations for each of the various baits (1× EAR = 1.18 m; 10× EAR = 2.00 m). A pole with six sticky traps spaced from 0.25-5.75 m in height had captures of Euwallacea sp. 1 yielding a mean flight height of 1.24 m with vertical flight distribution SD of 0.88 m (0.82-0.96 m, 95% CI). The SD with specific EAR was used to calculate EARc, two-dimensional EAR (1× EARc = 0.99 m; 10× EARc = 2.86 m), for comparison with other insect pheromone traps and for use in simulations. The simulation methods described previously were performed with combinations of 1-16 traps with 1-50 aggregations per 9-ha plot. The simulations indicate mass trapping with quercivorol could be effective if begun in spring before Euwallacea sp. 1 establishes competing sources of attraction.