Home > Phylum selection > Arthropoda > Hymenoptera > Blasticotomidae
Home How to cite this site Terms & conditions Disclaimer Contact Site tutorial / Help Links	Familia Blasticotomidae General information The Blasticotomidae are a species-poor hymenopteran family: there are only about 12 described species. However, the taxonomy of the family is still insufficiently known and advances in the knowledge of genus and species boundaries as well as discoveries of new species are likely to increase the number of species in the near future. Most species occur in eastern Asia (especially in Japan) and only a single species, Blasticotoma filiceti, also occurs as far west as Central Europe. Intriguingly, the only fossil record of the family is from the miocene of North America (Benson 1942) and this strongly suggests that the family formerly had a more global distribution. The imagines of the Blasticotomidae are medium-sized sawflies (also see Systematics below) (Fig. 1). Their body size ranges between 6 and 9 mm. A characteristic trait are the four-segmented antennae; however, the fourth segment, that is located at the distal end of the antennae, is very small and easily overlooked. Thus, the antennae appear three-segmented to the naked eye and this might lead to confusion with Argidae. Figure 1. Female imago of Blasticotoma filiceti filiceti. After Gauld and Bolton (1988). The larvae of the Blasticotomidae are elongate with well-developed thoracic legs, but without abdominal prolegs (Fig. 2). On the abdomen of the larvae two paired dorsal appendages on abdominal segments 8 and 9 are present. Their function, however, is unknown. Finally, there is a pair of cerci on the ventral side of segment 10. Figure 2. Older larval instar of Blasticotoma filiceti filiceti. Note the dorsal appendages at the posterior end. The first 7 abdominal segments and the first thoracic segment bear stigmata (openings of the respiratory system). After Shcherbakov (2006). Biology The Blasticotomidae have an interesting reproductive biology. Host plants are several species of ferns. The females deposit their eggs singly (in most cases) on the rachis of the frond. After hatching the larva bores a short canal into the rachis in which it lives and presumably feeds on sap. The canal is open at the rear end and the larvae often conceal this entry with a white foam (that becomes brownish with time) that emanates from the bore hole forming a foam plug that can grow the size of a walnut. This foam is reminiscent of similar secretions of spittlebugs (Aphrophoridae, Cercopidae), but is more solid and less watery (Fig. 3). How the larvae produce the foam is not understood, but rhythmic movements of the last abdominal segment appear to play a role. Not all larvae produce foam- often only a watery secretion is produced. The canal made by the larva is not much longer than the body of the animal. There are no canal systems typical of mines of other insects; even if a single frond is infested by several larvae their canals are always separated by thin walls of plant tissue. Therefore, the larvae of Blasticotomidae should not be classified as "leaf-miners". Older larval instars often bite one or two small holes at the front end of the canal, that are never concealed with foam. The place where the larva has entered the frond becomes characteristically brownish-black over time and the nearby pinnae are often crippled or withered (Fig. 3). The final instar appears to leave the canal and pupate in the soil, but this is not well-documented and rearing experiments in the laboratory were unsuccessful (except for one report by Wagner (1940)). It is likely, therefore, that the life cycle includes a so far unknown additional stage. The secretions and foam produced by the larvae appear to contain a large amount of sugar and attract other insects, especially ants (discovered by Shcherbakov (2006)), but also fruit flies use the secretions as food for their offspring. Despite the concealed lifestyle of the Blasticotomidae larvae they are often parasitized by braconid and chalcid wasps. Figure 3. Foam plug produced by a larva of Blasticotoma filiceti filiceti on a frond of a fern. Note the crippled pinnae next to the place where the larva has entered the leaf. After Shcherbakov (2006). Rearing and collecting Many aspects of Blasticotomidae biology are poorly understood and further research is therefore desirable. As already mentioned, rearing experiments so far were unsuccessful, likely because we still do not know the complete lifecycle. Other open questions are why the imagines are so rare, although the larvae can be quite frequent, and why no males have been found so far (see Blasticotoma filiceti). However, in Germany the Bundesartenschutzverordnung gives tight limits as to the collection and study of the German fauna, and anybody interested in studying German Blasticotomidae is advised to obtain the neccessary permits. Because of the rareness (at least of the imagines) the single German species Blasticotoma filiceti has been placed on the Red List of Endangered Species of most Bundesländer (e.g. Kraus et al. 2003) and is considered "critically endangered" nationwide (so-called "Gefährdungsstufe 2"). Some authors, however, doubt this assessment (Taeger et al. 1998). Systematics Ordo Hymenoptera - Hymenopterans, Hautflügler Subordo Symphyta - Sawflies, Pflanzenwespen Superfamilia Tenthredinoidea Familia Blasticotomidae - Farnblattwespen                           This page has been updated on May 4, 2013 This site is online since May 31, 2005 Copyright © by Nikola-Michael Prpic-Schäper. All rights reserved.	Search help Species list References HTD Nummer 2 Die Farnblattwespen Deutschlands (2011) Free PDF (2,1 MB)