Monacon sp. (Hymenoptera: Chalcidoidea: Perilampidae
Back to the wasps. This week we spotlight the genus Monacon, a small genus of 27 species in the old world Paleotropics of Africa, Asia, Australia and Oceania. The genus has not been found in the new world. Species of Monacon are parasitoids of Platypodidae (common names ambrosia beetles, pinhole borers). These are small beetles that bore into wood of various conditions – recently felled trees, dead, rotting wood, and trees in good condition. The beetles excavate galleries (up to 40 cm long!) in which they feed on ambrosia fungi. Some platypodid species are pests of economically important forest tree species. Monacon adults, although rare in collections, are easily differentiated from other Perilampidae genera by the presence of a horn arising in the middle of its face (see arrow). The horn may be used to break open the pupal case of the parasitoid when it finishes its development. Female Monacon probably locate potential hosts by homing in on sex pheromones (chemical attractants) released by male beetles. Female parasitoids do not directly attack the host beetle. Rather, the wasp lays its eggs in crevices of bark or under lichen. A mobile, sclerotized, larva with legs (a planidial type of larva, not the typical worm-like larva of most wasps) emerges from its egg and enters the gallery of the platypodid. Once inside the gallery the planidium searches out a nearly mature beetle larva and attaches itself to the host. After the pupal cell has been formed, the planidium larva moults into a normal looking worm-like larva. It is this form that consumes the developing beetle pupa. After finishing its own development, the adult parasitoid breaks out of its pupal case and exits the gallery. Monacon are apparently protandrous, with the males emerging before the females. This behaviour probably increases the chance of a male competing successfully for mates but comes with the risk to males that emerge too early of being preyed upon while waiting for females to emerge. Monacon species seem to be at least partly host-specific rather than specific to tree species.
A note on the hosts of Monacon. Platypodidae have a unique feeding behaviour (xylo-mycetophagy; =[wood] - [fungi] - [eating]). Adult beetles have pouch-like organs called mycangia in which they store fungal spores. While excavating a gallery these spores are spread over the gallery walls where mycelia (fungal ambrosia) develop from the spores. It is the ambrosia that are the food for the beetles.
Credits: Dr Robert Copeland