Species of Monacon are distributed from Africa to New Guinea and parasitize ambrosia beetles of economic significance to tropical forestry. This study, based on fieldwork in Papua New Guinea and in Seram, Indonesia, provides the first detailed examination of the interaction between
these parasitoids and their hosts; Monaconrobertsi is a solitary, monophagous ectoparasitoid of the pupa of Crossotarsus barbatus. The phenology of the parasitoid and its host are summarized with life-history diagrams, and information is presented on oviposition, distribution
of parasitoids within the gallery system constructed by the host, behaviour of adults both within and outside the gallery system, and sex ratios. A sex pheromone produced by male C. barbatus during the initiation of a gallery system both reinforces host specificity and synchronizes
oviposition by Monaconroberstsi with mating of the host. This results in the parasitoid attacking only the first few of many host egg batches, which reduces the overall parasitism rate. Monaconroberstsi eggs are strongly sculptured, suggesting plastron respiration,
and are laid on the bark in the vicinity of the entrance to ambrosia beetle galleries. Development is hypermetamorphic; the first instar is a heavily sclerotized planidium that locates and attaches to the host, and subsequent larval instars are grublike and hymenopteriform. The planidia experience
high mortality rates while transferring to successive host instars and only a single planidium remains when metamorphosis and feeding begin, which coincides with host pupation. The immature stages of M. robertsi are described and illustrated using both light and scanning electron microscopy
and are compared with those of other genera of Perilampidae and with Eucharitidae. The potential of Monacon species as agents of biological control of economically important species of ambrosia beetles is discussed and judged to be poor.
Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.