The Life and Times of Diaulomorpha

Diaulomorpha is a fairly typical genus of the diverse micro-wasp family Eulophidae. Like most other eulophids, members of this genus are slender with a relatively soft metasoma. The mesosoma, on the other hand, is tougher, weakly vaulted, and conspicuously reticulate dorsally. Members of the genus are known from Australasia and South America (Bouček 1988).

Body of female Diaulomorpha itea, from Bouček (1988).

Diaulomorpha species are parasitoids of insect larvae that live as miners in leaves. They are known to feed on both Lepidoptera and Hymenoptera larvae; it seems that it is not the identity of the host that attracts them but the lifestyle. They are multivoltine, that is they can go through multiple generations in the course of a year. The breeding cycle and behaviour of a Diaulomorpha species was described by Mazanec (1990) as a parasitoid of the jarrah leafminer Perthida glyphopa, a moth whose larvae attack the leaves of jarrah Eucalyptus marginata.

Mating between males and females occured after a brief courtship ritual in which the pair each extended their wings upwards and beat them up and down. Females located host larvae by running across the leaf surface and drumming the outside of prospective mines with their abdomen. They would then drill into the mine with their ovipositor, though of course the host larva would generally be trying to escape the wasp's attentions; a female might have to drill several holes before successfully piercing the caterpillar. The ovipositor would then be 'stirred' into the host to cause haemolymph and other fluids to leak out of its skin, and the wasp would feed on this fluid through the hole formed by the ovipositor. Egg laying would begin shortly after the wasp had finished feeding. Egg production was relatively slow, with only five or six eggs able to develop within the mother at a time, and the female wasp would lay through a newly created hole into the mine near the selected host. Usually only one egg would be laid in a mine but sometimes multiple eggs would be laid and the emerging larvae would share the host individual. After laying an egg, the female would tap around the laying hole with the tip of her metasoma, presumably depositing some chemical that would signal to other Diaulomorpha females that the mine had already been attacked. The host, meanwhile, would stop feeding after being stabbed with the female's ovipositor and would finally die after about a day and a half. It was around this time that the larva(e) would hatch and commence feeding on its remains.

Though healthy hosts would obviously be preferable, female Diaulomorpha were not above attacking hosts that had already died or had already been parasitised by other wasps. Such hosts were particularly likely to be attacked by young females that had not yet learnt to deal with the defensive actions of a healthy host. Deceased hosts could present a problem in that their bodily fluid pressure had been lost, and the female might have to stab them with her ovipositor several times before she had ingested enough fluid to begin laying. Pre-parasitised hosts were less of a problem as endoparasitic wasp larvae within the host would die after the Diaulomorpha's stab along with the host.

Mazarec (1990) found parasitism levels by Diaulomorpha within the host population to be low. What is more, as host populations increased the level of parasitism would plateau, so the proportion of parasitised hosts was far lower in dense host populations. This presumably resulted from the wasp's low rate of egg production: as host populations increased, the population of wasps did not keep up with it. As such, the role of Diaulomorpha in pest control is probably limited.

REFERENCES

Bouček, Z. 1988. Australasian Chalcidoidea (Hymenoptera): A biosystematic revision of genera of fourteen families, with a reclassification of species. CAB International: Wallingford (UK).

Mazanec, Z. 1990. The immature stages and life history of Diaulomorpha sp. (Hymenoptera: Eulophidae), a parasitoid of Perthida glyphopa Common (Lepidoptera: Incurvariidae). Journal of the Australian Entomological Society 29: 147–159.