Fungus Cultivation by Ambrosia Beetles: Behavior and Laboratory Breeding Success in Three Xyleborine Species

Fungus cultivation by ambrosia beetles is one of the four independently evolved cases of agriculture known in animals. Such cultivation is most advanced in the highly social subtribe Xyleborina (Scolytinae), which is characterized by haplodiploidy and extreme levels of inbreeding. Despite their ubiquity in forests worldwide, the behavior of these beetles remains poorly understood. This may be in part because of their cryptic life habits within the wood of trees. Here we present data obtained by varying a laboratory breeding technique based on artificial medium inside glass tubes, which enables behavioral observations. We studied species of the three most widespread genera of Xyleborina in the temperate zone: Xyleborus, Xyleborinus, and Xylosandrus. We raised several generations of each species with good breeding success in two types of media. The proportion of females of Xyleborinus saxesenii Ratzeburg producing offspring within 40 d depended significantly on founder female origin, which shows a transgenerational effect. Labor-intensive microbial sterilization techniques did not increase females' breeding success relative to a group of females shortly treated with ethanol. Gallery productivity measured as the mean number of mature offspring produced after 40 d varied between species and was weakly affected by the type of medium used and foundress origin (field or laboratory) in X. saxesenii, whereas different preparation and sterilization techniques of the beetles had no effect. Behavioral observations showed the time course of different reproductive stages and enabled to obtain detailed behavioral information in all species studied. We propose that the laboratory techniques we describe here are suited for extensive studies of sociality and modes of agriculture in the xyleborine ambrosia beetles, which may yield important insights into the evolution of fungal agriculture and advanced social organization.