Predicting the distribution ofEccritotarsus catarinensis, a natural enemy released on water hyacinth in South Africa

Abstract

Water hyacinth [Eichhornia crassipes (Mart.) Solms (Pontederiaceae)] is the most damaging aquatic weed in South Africa, where five arthropod biological control agents have been released against it. The most recent introduction of Eccritotarsus catarinensis (Carvalho) (Heteroptera: Miridae) has failed to establish permanent populations at a number of sites in South Africa where water hyacinth is a problem. Cold winter temperatures at these sites are assumed to be the reason for these establishment failures. This assumption was tested by investigating the thermal physiology of the mirid, then incorporating these data into various predictive distribution models. Degree‐day models predict 3–14 generations per year at different localities in South Africa, and five generations at a Johannesburg site where the mirid failed to overwinter. The inability to develop sufficiently rapidly during winter months may hinder overwintering of this insect, which was predicted to develop through only one generation during the winter months of April to August in Johannesburg. A CLIMEX model also showed that cold stress limits the mirid's ability to overwinter in the interior of the country, while determination of the lower lethal limit (–3.5 °C) and critical thermal minimum (1.2 ± 1.17 °C) also indicated that extreme temperatures will limit establishment at certain sites. It is concluded that E. catarinensis is limited in its distribution in South Africa by low winter temperatures.

Management of water hyacinth (Eichhornia crassipes [Mart.] Solms) using bioagents in the Rift Valley of Ethiopia

“…Data on the developmental threshold and degree-day requirements (CLIMEX PDD parameter) indicates that the two weevils would complete a number of generations per year (> 4.5). In agreement with that, Coetzee et al (2007) reported successful establishment of the agents if the bioagent had > 1 generation year -1 .…”

“…However, no difference was observed regarding numbers of remaining ramets and leaves in the combined application of three pairs of N. bruchi with two and three pairs of N. eichhorniae. Leaf number and ramet production are among the most critical growth factors that limit water hyacinth survival (Center and Van, 1989;Heard and Winterton, 2000;Coetzee et al, 2007) and are therefore proper parameters to evaluate the impact of weevil herbivory. Asexual reproduction by water hyacinth is important in the density and spread of water hyacinth populations.…”

“…Subsequent evaluations have demonstrated that it affects water hyacinth growth (Coetzee et al, 2007) and competitive ability (Coetzee et al, 2005;Ajuonu et al, 2009), by reducing the plant's overall vigour. Eccritotarsus catarinensis has also been released in Zimbabwe, Zambia, Malawi, Benin, and China but only established in Malawi (Coetzee et al, 2009a).…”

“…Similarly, Martinez and Gomez (2007) indicated that combined application of Neochetina weevils with A. zonatum showed 65% reduction in number of green leaves and 85% reduction in new ramets. Leaf number and ramet production are among the critical growth factors that affect water hyacinth survival (Center and Van, 1989;Heard and Winterton, 2000;Coetzee et al, 2007). Vegetative multiplication is key for the density and spread of water hyacinth populations.…”

“…In line with that, efforts are being made to assess the integration of insect pests and fungal pathogens for the management of water hyacinth (Moran, 2005(Moran, , 2006Martinez and Gomez, 2007). Similarly, research is being conducted to complement the effect of weevils with other arthropods in the management of water hyacinth (Coetzee et al, 2007).…”