Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation of Colophospermum mopane savanna by Imbrasia belina larvae

Severe defoliation is expected to affect nutrient cycling of an impacted system. Outbreaks of the lepidopteran Imbrasia belina (mopane worm) affect discrete patches of Colophospermum mopane trees in semi-arid savanna; larvae may completely defoliate trees for up to six weeks during each of the early and late growing seasons. We studied the impact of mopane worm outbreaks on the availability of nitrogen, phosphorus and potassium within mopane savanna by comparing defoliated with non-defoliated savanna patches. Individual studies conducted were production and nutrient content of leaf biomass and worm frass that determine nutrient input to the soil, and soil nutrient concentrations. Within an outbreak area 44 percent of trees supported ±29,000 worms/ha who deposited ±640 kg/ha dry weight of frass at 1.4 g of frass/day (fourth or fifth instar) compared with an average 1645 kg/ha dry weight of leaf on trees most of which should be deposited by litter fall at the end of the growing season. Nu...