Effects of Organic Soil, Pit Sand and River Sand on Pupation, Survival and Emergence of Gonimbrasia belina

Abstract

The mopane worm, Gonimbrasia belina, is a vital edible insect in southern Africa, with its pupal life stage being critically dependent on soil substrate properties. This study evaluated the effects of organic soil (OS), pit sand (PS) and sandy soil (SS) on pupation success, survival and moth emergence of G. belina in southern Zimbabwe across natural habitats and controlled greenhouse environments. Field results showed that OS supported the highest densities of live and dead diapausing pupae, especially in pure mopane woodlands, reflecting the importance of organic matter for moisture retention. PS consistently outperformed SS, suggesting substrate texture influences pupal survival more than regional climatic variation. In greenhouse trials, PS substrates yielded the highest moth emergence rates, while mulch additions paradoxically increased live pupae but reduced emergence success. Mortality rates did not significantly differ among substrates, indicating external factors may drive pupal mortality in the wild. Seasonal and microhabitat conditions also influenced emergence, with wet seasons favouring moth eclosion. These findings highlight the trade-offs between pupation success and emergence, informing sustainable rearing practices and conservation strategies. Protecting organic-rich soils in mopane woodlands and prioritising PS substrates in captive breeding can enhance mopane worm production, which is crucial for food security and rural livelihoods under changing environmental conditions.