Insect of the week: 10 July 2023

A species of Valgus is our insect of the week (32).

Valgus is a genus of scarab beetle of the familiar subfamily Cetoniinae, Tribe Valgini. Many Cetoniinae are large and showy insects and they are often bought and sold by collectors. Aesthetically, our “electric” Valgus species compares favourably with other members of the subfamily, though a bit on the small size at ca. 8 mm in length. Fossil Valgus are rare, with one specimen found in France in sedimentary Diatomitic rock dated to the late Miocene, ca. 5.6 million years ago. Worldwide, Valgus comprises 17 species (Catalogue of Life online), most of which are known from the Palearctic region and Asia. Although distributed worldwide, the genus is depauperate in Africa where it is known from a single species (Valgus smithii) described from South Africa. However, five undescribed Valgus species are known from Kenya, in private collections. Those species of Valgini for which there is some behavioural data, are often found as adults on flowers where they feed on nectar and pollen, the latter an important nutrient for egg production. Flowers of the Rosaceae, Apiaceae and Brassicaeae are favoured. Valgus larvae are saproxylic, feeding on dead and rotting wood. Adult females have a long pygidial spine with which they are thought to shape the woody substrate prior to egg laying. The mating behaviour of one species of Valgus has been observed and is interesting in that the males lie on their backs, presumably because the females pygidial spine is in the way. Given their larval ecology it is no surprise that they are often found in woodland and forested areas. Valgus shares its diet with hundreds of other saproxylic species, mostly Coleoptera and Diptera. They are all part of an army of insect species which break down wood into its constituent elements and molecules, recycling nutrients back into the forest floor and sustaining plant growth. The recycling of dead wood in forested areas is critical for the growth of healthy vegetation, and the removal of dead wood from the forest to be used by humans for firewood reduces this source of nutrients and is a limiting and negative factor in the forest environment. Our insect of the week was collected on flowers in a small forest-clearing at an elevation of ca. 2000 m ASL, in Castle Forest on the southern slopes of Mt. Kenya. The high elevation places Valgus in the Afromontane region and is considerably higher than the distribution records of the aforementioned, undescribed Kenyan species which are found at low elevations, suggesting that our specimen likely represents a new species.

Credits: Dr Robert Copeland