Exploring the fine line between ecology, conservation and utilisation of a commonly exploited resource: A case study of mopane worms (Gonimbrasia belina) in southern Africa

Abstract

Mopane worms, the larvae of the mopane moth (Gonimbrasia belina), have a wide distribution in south and central Africa. They are valued highly as a food source and thus create local income in rural areas. They also contribute to ecosystem services by being part of the food chain and facilitating nutrient cycling on a landscape level. However, mopane worms are threatened by high harvest rates, habitat loss and the changing climate. Significantly, the existing research focuses on the utilisation of mopane worms, such as nutrient content, for human consumption. Very little research is done on mopane worms' ecology and their ecological contribution and importance. This study aims to determine the extent of mopane worms’ distribution across southern Africa, specifically in relation to protected and non-protected areas, to evaluate to what extent harvesting is restricted or can potentially be addressed, as well as determine the potential ecosystem services of mopane worms by measuring the consumption rate and frass production on a landscape scale and comparing nitrogen release through mineralization from frass and mopane leaves. This was achieved through four main objectives: 1) review current research to evaluate the type of research topics, consolidate current knowledge, and identify gaps and future research directions; 2) quantify the suitable habitat of mopane worms in several southern African countries; estimate the effectiveness of protected areas to capture suitable habitat, and, explore variables affecting the suitable habitat of mopane worms; 3) assess the impact of mopane worms on the mopane veld ecosystem in Mapungubwe National Park through herbivory and 4) compare the N mineralisation rate as indicated by N-NH4 and N-NO3 release from frass from mopane worms and leaves from mopane trees, to establish whether the presence of mopane worms’ frass leads to faster nutrient release for plant uptake. The review found that most studies focus on mopane worm utilisation, such as their importance as a food and income source, while very few research efforts focus on biology or ecology. Although research on mopane worms has drastically increased over the years, these research efforts are not equally distributed among African countries, with most studies being done in South Africa, while other countries have very few or even no studies. Presence-only modelling identified the suitable mopane worm habitat and correlated this with protected and unprotected areas. Most of the harvesting occurs in non- protected areas, where there are relaxed regulations on harvesting. The extent to which mopane worms contribute to defoliations and frass production, was determined by measuring and calculating the consumption rate and frass production for the landscape. Data show that a wide variation exists, which can be due to factors such as weather patterns, type of vegetation, predation, etc. This was followed up with a laboratory incubation trial to determine the difference between nutrient release from mopane worm frass (when a healthy population of mopane worms are present) with the mineralization and nutrient release from mopane leaves (when no mopane worms are present). More nutrients are released from frass compared with leaves, indicating that mopane worms facilitate nutrient cycling in the landscape. This study highlighted the significance of mopane worms in the natural environment and then provided a suitable habitat for the worms that need management to ensure their sustainability.