South Africa is a hotspot for previously unknown stem-boring wasps of grasses (Tetramesa; Eurytomidae)
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The stem-boring wasp genus Tetramesa (Hymenoptera: Eurytomidae) comprises 203 species that feed exclusively on grasses. The wasps are highly host-specific, typically feeding on a single or a few closely-related grasses, and can cause significant damage to their host grass (e.g. reducing seed production, increasing tiller mortality). These attributes often result in Tetramesa being serious grain pests, but it also makes them ideal biological control agent candidates for controlling invasive grasses. Very little is known about the Afrotropical Hymenoptera in general, and to date, almost all the sampling effort in collecting and describing Tetramesa species has taken place in the northern hemisphere. Only four African species have been described; none of which are from South Africa. The Centre for Biological Control (CBC) at Rhodes University has been investigating biological control options for several African grasses that have become invasive in Australia and the Americas, and have been collecting Tetramesa specimens across South Africa since 2017. The insect communities associated with more than 60 different native grasses have been surveyed over this period. The uniform morphology of adult and larval Tetramesa has, however, made it impossible to determine whether these wasps are a single polyphagous species, or multiple oligophagous and/or monophagous species. We are currently using genetic barcoding tools (mitochondrial COI and nuclear ITS2 regions) and species delimitation methods to solve this problem. Our preliminary results have identified at least six potentially undescribed Tetramesa species from South Africa. Each novel Tetramesa species was highly specific, with five of the six potential species feeding and completing their development on a single host grass species. This work will facilitate using biological control techniques to manage invasive alien grass species and highlights a previously unknown diversity of Tetramesa species associated with South African grasses. It is likely that we will uncover many more undescribed Tetramesa species in the region as our sampling effort escalates.
Citation: Sutton, G.F., van Steenderen, C.J.M., Canavan, K., Yell, L., & Paterson, I.D. (2021). South Africa is a hotspot for previously unknown stem-boring wasps of grasses (Tetramesa; Eurytomidae). 56th Annual Congress of the Grassland Society of Southern Africa (27 - 29 July 2021), Online Event.