Ten years after the release of the water hyacinth mirid Eccritotarsus catarinensis in South Africa: what have we learnt?

Abstract

AbstractWater hyacinth, Eichhornia crassipes (Mart.) Solms, is the worst aquatic weed in South Africa, and biological control offers the most sustainable control option. The mirid, Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae), was released against water hyacinth in South Africa in 1996 and shown to be damaging to the plant and host-specific within the Pontederiacae. Feeding, oviposition and nymphal development were recorded on pickerelweed, Pontederia cordata L., an important aquatic plant in North America but a potential weed in South Africa. The release of this agent allowed us to test in the field that pickerelweed was not part of the mirid's realized host range. The agent subsequently established at 15 sites around South Africa, including those where climatic modeling had indicated that it would not due to low winter temperatures, calling into question the usefulness of climate-matching techniques in the absence of microclimate and behavioural data. Hypertrophic nutrient conditions also reduced the effectiveness of E. catarinensis due to rapid proliferation of the plant, but the mirid reduced both the vigour and competitive ability of water hyacinth in mesotrophic and eutrophic water. E. catarinensis is emerging as an effective agent in areas of medium to lownutrient status with a warm climate and should be considered for release in other areas of the world, particularly Africa, where few Pontederiaceae occur. This programme shows the value of considering fundamental vs realized host ranges but suggests that more data are needed to increase confidence in climate compatibility predictions.