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Catchment context and the bottom-up regulation of the abundance of specialist semi-aquatic weevils on water hyacinth


Matthew F. Purcell, CSIRO Ecosystem Sciences, PO Box 2583, Brisbane, QLD 4001, Australia. E-mail:


1. Bottom-up regulation is prevalent in plant–herbivore interactions and is thought to be particularly important in the case of aquatic plants and their specialist insect herbivores.

2. Recently published mesocosm studies have shown that the abundance of specialist Neochetina weevils, N. bruchi and N. eichhorniae, on water hyacinth (Eichhornia crassipes) are principally under the influence of nutrients in plant tissues.

3. We examined historical patterns of the abundance of these species of semi-aquatic weevils in two water bodies from catchments with significantly different nutrient loads in subtropical Australia to test the validity of the published conceptual model of bottom-up regulation.

4. Our results revealed that these weevils are indeed under bottom-up regulation under field conditions. However, the nature of this regulation appears to be influenced by the broader catchment context of the water hyacinth-infested water body, with plant tissue nutrients influencing weevil abundance more in the catchment with lower nutrient run-offs.

5. Our findings reaffirm the importance of bottom-up regulation in plant–insect interactions, add to the growing evidence of indirect effects spanning terrestrial and aquatic ecosystems, and inform management of water hyacinth using these weevils as biocontrol agents.