Insect of the week: 17 July 2023

Mantibaria sp., Scelionidae: Scelioninae: Mantibariini

The genus Mantibaria is nearly cosmopolitan, a recent record from the neotropics (Central and South America) is thought to represent an accidental introduction. Although 3-4 species of Mantibaria are known, most taxonomists consider them all to be synonymous with the type species. If so, that is an impressive distribution record for a single species. Mantibaria species are obligate feeders on praying mantids. Moreover, females are phoretic in that they remain on the host mantid enjoying, no doubt, free rides through the countryside as the mantid goes about its business. Morphologically, Mantibaria is unique, and currently placed in a separate tribe, Mantibariini. It is also rare in its feeding behaviour, combining elements of the parasite and parasitoid life histories. An explanation might be useful here. A parasite may be external or internal but usually does not kill the host, although there are important exceptions, such as falciparum malaria which is often lethal. A parasitoid may also be external or internal but differs from a parasite in always being lethal to the host. To complicate matters a bit, some researchers consider that the larval phase of Mantibaria’s life cycle is not exactly that of a typical parasitoid, since a single Mantibaria larva has been observed to eat the contents of multiple mantid eggs. A term suggested for this behaviour is “pseudoparasitoid”. 

The first specimens of Mantibaria were collected on emergence from an egg mass of Mantis religiosa. In attacking mantids one might think that Mantibaria places itself at serious risk, attacking one of the great predators of the insect world, the praying mantid. In fact, Mantibaria’s small size is her best weapon. There is evidence that the mantid can detect the presence of the adult Mantibaria but is unable to contort itself enough to bend around and grab it. In her arsenal of tricks once she lands on a mantid, Mantibaria does the unthinkable, proceeding to shed about 2/3 of its own forewing length (black arrow; see image), a practice called dealation. What good does that do, you ask? Well, the adult female needs to station itself just under the base of the mantid wing. Perhaps reducing its size by jettisoning much of its wing makes it easier for Mantibaria to move around in the narrow space between the mantid wing and its body. After settling under the base of the mantid wing, Mantibaria acts as a true parasite making a small wound in the integument of the mantid and feeding on the haemolymph of its host. Mantibaria is probably able to maintain its position on the mantid by means of the tarsal claws at the apex of each leg and what appear to be modified, enlarged, lobe-like arolia (red arrow) lying between the two tarsal claws. The apical 2/3 of each arolium is white, the basal 1/3 brown. It is tempting to speculate that the arolia act as attachment organs to maintain the hold that Mantibaria has on the mantid integument, perhaps in a manner like that of some species of stick insects. Female Mantibaria may also be found between segments of the mantid abdomen. When the mantid starts to oviposit the adult female Mantibaria moves to the end of the host abdomen and climbs onto the host egg mass, laying its eggs in or on those of the mantid. Mantibaria’s eggs hatch and its larvae consume the contents of the host eggs. End of story, three cheers for the little guy. We collected our Mantibaria specimen in Lambwe Valley, western Kenya across from little known Ruma National Park.

Credits: Dr Robert Copeland