The highly diverse and economically important parasitoid Wasp superfamily Chalcidoidea is well known with approximately 20 000 extant species on six continents, but relatively few fossil species are known. However, a broad range of Chalcidoid fossils from the Eocene have been described. Two of these fossils, Perilampus pisticus and Palaeocharis rex represent the biologically derived Planidial group. This unique group of parasitoids is characterized by mobile and well sclerotized (thick skinned), but legless, first instar ‘planidial’ larva, which emerges from an egg laid some distance from the host instead of on or in the host. Later instars are of the sac-like type that is typical for Chalcidoidea.
In a paper published in the journal Insect Systematics and Diversity on 13 December 2019, Roger Burks of the Department of Entomology at the University of California, Riverside, Lars Krogmann of the Staatliches Museum für Naturkunde and the Institute of Zoology at the University of Hohenheim, and John Heraty, also of the Department of Entomology at the University of California, Riverside,describe a new species of Planidial Chrysolampine Wasp from Eocene Baltic Amber.
Baltic amber is the preserved resin of Eocene Coniferous Trees that formed huge forests covering much of Scandinavia and Northern Europe between about 56 and 34 million years ago. Since this amber floats, it is often found on beaches around the Baltic Sea, and sometimes further afield, making the precise dating of individual pieces difficult, though most Baltic Amber is thought to be about 46 million years old.
The new species is placed in the extant genus Brachyelatus, and given the specific name marthae, in honour of Roger Burks' mother, Martha. The species is described on the basis of five specimens, four females ranging from 1.3 to 1.9 mm in length and a male measuring 1.3 mm, and is assigned to the genus Brachyelatus on the basis of the pattern of veins in the wings (commonly used as a way to differentiate Insect species).
Brachyelatus marthae. (1)–(5) Females, (1) Habitus (SMNS BB-2843). (2) Body in dorsal view (SMNS BB-2842). (3) Body in lateral view (SMNS BB-2844). (4) Body in ventral view (SMNS BB-2842). (5) Forewing venation (SMNS BB-2842); cs, uncal sensilla. (6) Male, head, anterior view (SMNS BB-2846); atp, anterior tentorial pit; Fu1, first funicular (second flagellomere); vp, ventral pores of scape. Burks et al. (2019).
The reproductive biology of modern Planidial Wasps is best known from studies of the genus Chrysolampus, which lays stalked eggs into seed pods within flower heads, which produce weakly sclerotized larvae search for their weevil host within the seed pods. Members of the genus Austrotoxeuma are potentially associated with Beetles in dead twigs, but otherwise, there is no other biological information for the subfamily. The genus Brachyelatus is known from three described and one undescribed species known from Europe, Transcaucasia, Australia, and Turkey, so the discovery of a species in Eocene Baltic Amber does not expand it's geographical range, but does increase the known temporal range of the genus and subfamily by an estimated 36 million years.
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