Megastigmus wasp damage to seeds of Schinus molle, Peruvian pepper tree, across a rainfall gradient in South Africa: implications for invasiveness.
Schinus molle, a shade-tolerant evergreen tree from Peru, was introduced into South Africa for use as an ornamental and shade tree in the middle 1800s. The species is spreading in disturbed sites and in natural communities where it forms dense canopies that can completely shade out and displace native vegetation in the semi-arid savannah regions of South Africa. A total of 100 fresh ripe seeds of S. molle (with red pericarps) were collected beneath each of 30 randomly selected trees from winter and summer-rainfall regions (Western and Northern Cape Provinces of South Africa). The native seed-feeding wasp Megastigmus transvaalensis was identified as the main seed predator of S. molle in both regions. The total seed damage observed in S. molle was significantly greater in the summer-rainfall than in the winter-rainfall region for the localities sampled, and was largely attributed to feeding damage by the developing larvae of M. transvaalensis. There was no difference in the mean percentage of rotten seeds between the 2 regions. However, the relative proportion of insect-damaged seeds was significantly greater in the summer-rainfall population than in the winter-rainfall population.