"More than twenty years too late for his scientific reputation, and after having done an amount of injury almost inconceivable in its immensity, Francis Walker has passed from among us". (from an obituary of Walker written by an anonymous contemporary).
The genus Chalcedectus is our Insect of the Week. The genus was erected by the notorious British taxonomist Francis Walker in 1852. Reading the name Walker (impossible to avoid because of the ca. 16,000 species he described) is enough to make taxonomists grind their teeth. Walker stirred controversy during his later life (and continuing to the present) because his publications resulted in the creation of a large number of junior synonyms (a junior synonym is a name given to a species that has already been described under a different name). Considering the huge number of species he studied, it is perhaps no surprise that Walker often described the same species under different names, having forgotten that he published them previously. Much of modern taxonomy is taken up with the task of correcting his errors.
Until recently, Chalcedectus was placed in the taxonomically confusing family Pteromalidae for a very long time contained genera that could not be comfortably assigned to any of the other families that make up the huge and biologically important superfamily Chalcidoidea. With the recent use of DNA analysis, most of the confusion has been resolved, with the result that many of the pteromalid genera, tribes and subfamilies have been elevated to family rank, more than doubling the number of families in the Chalcidoidea to 50. One example was the elevation of Chalcedectus, together with one other genus, Agrilocida, to the family Chalcedectidae. Agrilocida is a monotypic genus, one species known only from the Palearctic region.
Chalcedectus comprises 20 species. Most species are neotropical and none have been described from the Afrotropical region. However, two undescribed species are known, one from South Africa and one from the Central African Republic. In Kenya, we have collected over 100 Chalcedectus specimens representing 5 species. Currently, the Afrotropical species are being studied and will probably reveal a rich Afrotropical fauna.
Chalcedectus is easily identified. Both sexes possess enlarged hind femora with a row of small teeth. That alone eliminates the great majority of Chalcidoidea families, leaving only Chalcididae, Leucospidae and Torymidae. Various morphological features such as differences in wing venation, orientation of the eyes, possession or lack of metallic colouration highlights, fusion of male abdominal segments, and storage of female ovipositors separate chalcedectids from the other three families with swollen hind femora. Often, it is difficult to separate the sexes of tiny chalcidoid specimens. One nice feature of the genus Chalcedectus is the presence, in females, of a filamentous bristle at the end of the antennae (see image). Males lack this feature.
Chalcedectus are parasitoids of xylophagous wood-boring beetles, including Cerambycidae (Longhorn beetles) and Buprestidae (jewel beetles). Along with other microhymenopteran parasitoids they attack larvae of the Rosaceae Longhorn Beetle, Osphranteria coerulescens Redtenbacher, a pest that can severely damage the stems of rosaceous shrubs and small trees, including the important species of fruit trees (plum, pear, cherry, peach, etc.). So, three cheers for Chalcedectus and the other microhymenoptera!