Understanding spatial structuring and the role of domestication in the development of sustainable harvest techniques of Mopane worms (Gonimbrasia belina).

Abstract

Mopane worm (Gonimbrasia belina Westwood) is an indigenous edible insect that periodically has population eruptions in Mopane tree (Colosphermum mopane) dominated vegetation. This insect is a valuable source of food and has become an economic commodity for commercial harvesters. Despite its importance, little is known of the population dynamics of mopane worm. Considerable attention has been paid to the nutritional and social dimensions of mopane worm consumption. However, anecdotal evidence suggests there is a decline in the spatial extent of their distribution due to unsustainable utilization, land transformation, and commercialization. This is paralleled with a decrease of harvest yield, thereby affecting local communities, commercial harvesting operations, and market product availability. Partial domestication of this species may be a way of ensuring sustainable and reliable utilization of this edible insect because it improves natural survival rates. Here I explore mopane worm ecology by mainly focusing on understanding spatial structuring and the role of domestication in the development of sustainable harvest techniques of Mopane worms (G. belina). Spatial structuring of mopane worms was investigated at both a fine (10m x 10m) and medium-scale (1 km2) at sites with and without commercial harvesting. Mopane worm populations were experimentally treated through transplant experiments and manipulating access of predators to 1st – 3rd instar larvae. The role of tree characteristics (height, canopy volume and number of stems) on both spatial and experimental treatments were explored using generalized linear mixed models. Moran’s Eigenvector Maps (MEM’s) were used to represent spatial structures at various scales and the role of soil. Relative to control, seeding of worms was successful in establishing new populations in unoccupied areas while transplant and application of sleeve nets had no significant effect on larval survival. Populations at sites where no harvesting takes place were spatially structured, while this was not true where commercial harvesting takes place. Canopy volume also accounted for egg packets distribution although the relationship was ambiguous. The density of larvae increased with an increase in sodium concentration in soil. Seeding of the population provides a viable option for the sustainable utilization of mopane worms and educating people on how to domesticate mopane worms. This study also highlights that populations of mopane worms are not only clumped in time but also in space and at various spatial scales.