AMBRO'SIA BEE'TLES. Beetles of the family Scolytid:e, which differ from the bark bo•ers by pushing their galleries deeply into tim herwood and feeding upon a substance called "am brosia." They include the genera Xylebo•us, Platypus, Co•thylus, and their allies, and are com mon and often injurious throughout North America. All are very small, elongate, compact beetles, of the form shown in the illustrations of their work on the Plate illustrating ARMY WORM and AMBROSIA BEETLES, and their cylin drical galleries rarely exceed a tenth of an inch in diameter. These galleries penetrate the solid wood deeply, ramify widely, are uniform and free from dust, and have many short branches, serv ing as brood-cells; their walls arc stained, and the perforations and stain injure the wood for many uses, although not sullicBmt to harm the life of the tree perceptibly. The most interest ing feature of their history is the care given to their young, and the cultivation of fungi—acts unique among beetles, and comparable to those cf the social hymenoptera. Habits and methods vary among the different genera, hut in general are as follows: Within their galleries is found a substance, taking various forms. most usually that of a cluster of chains of heads, which has been named "ambrosia,'' and which is shown by the microscope to be a fungus. This fungus is succulent, and forms the food of the insects and their young, and it is planted and cultivated by these beetles, which regard its safety with the ap parently anxious solicitude that bees feel toward their stores of honey food. It is started by the
mother insect upon a carefully prepared bed of wood dust, sonic species devoting, special cham bers to this purpose, others starting a bed any where near the larva., using the excrement of the larvae as an aid to its propagation. Sap must be present, however. in order to secure its growth, and in most species the sap must be in a condi tion of fermentation. Then the fungus must be eaten as it grows—kept grazed down—or it will ripen, emit spores, and choke up the tunnels. All these difficulties are so well met by these minute gardeners that many generations in suc cession sometimes inhabit and continue to en large their system of galleries. These are some times bored in vigorous timber, but more often in weak trees, and dead wood is sometimes occupied, certain species exhibiting a special predilection for the staves of wine casks. A full treatment of this group and their customs and effects has been given by H. G. Hubbard, United States Depart ment of Agrienit um new series, Dirision of En tomology, Bulletin :Vo. 7 (Washington, 1897).