Granulate Ambrosia Beetle

Family Curculionidae subfamilies Scolytinae and Platypodinae together contain about 3,500 species of 'ambrosia beetles' — wood-boring beetles that practice OBLIGATE FUNGUS AGRICULTURE. The behavior independently evolved in beetles approximately 60 million years ago and is one of only a few cases of true agriculture in the animal kingdom (the others being leaf-cutter ants, Macrotermes termites, and recently-discovered marsh-grass-farming snails). The agricultural cycle: a female ambrosia beetle carries spores of her symbiotic 'ambrosia' fungus in specialized body pouches called mycangia (typically located in the head, prothorax, or near the mandibles, depending on the beetle group). She tunnels into a stressed or dying tree, excavates a brood gallery in the sapwood, and inoculates the gallery walls with her mycangial fungus. The fungus grows on the gallery walls (typically Ambrosiella, Raffaelea, or related Ascomycota species), and the beetle and her larvae feed exclusively on the fungal mycelium and conidiophores — they do not consume the wood itself. The fungus also breaks down the wood toxic compounds that would otherwise kill the beetle. The relationship is obligate: beetle and fungus cannot survive separately. Xylosandrus crassiusculus, the granulate ambrosia beetle, is a particularly destructive Asian species that has invaded the southern US and now kills nursery, orchard, and ornamental trees across the region by introducing pathogenic strains of Fusarium and other fungi alongside the ambrosia symbiont. The species is one of the most-monitored exotic forest pests in current USDA APHIS surveillance.