Anthropogenic disturbance affects specialist, but not generalist, endophagous insects associated with two African grasses: implications for biological control

ABSTRACT

The specialisation-disturbance hypothesis (SDH) predicts that specialist and generalist taxa respond differently to disturbance, with generalists more tolerant of disturbance, while habitat stability (i.e. no/limited disturbance) should favour specialist species. If the SDH holds true, this would have implications for the design and implementation of biological control programmes, in terms of performing native-range surveys in search of candidate agents and subsequent development of management programmes for their release in the weeds invaded range. We assessed the effect of anthropogenic disturbance (mowing/slashing and fire) on the endophagous insect communities associated with two African grasses, Sporobolus pyramidalis and Sporobolus natalensis (Poaceae), that are targets for biological control in Australia. Comparisons, of insect community structure and presence/abundance of each species between disturbed and undisturbed sites, were made at 19 sites in South Africa. Disturbance caused a shift in insect species composition and abundance, whereby specialist insects were less frequently encountered and less abundant at disturbed versus undisturbed sites. If the potential agents for Sporobolus spp. are released in Australia they may be negatively affected by disturbance and may therefore be incompatible with certain integrated management strategies, such as mowing and prescribed burning. Moreover, our results suggest that field sites with limited disturbance should be prioritised during native-range surveys to maximise the chances of locating specialist natural enemies. The effect disturbance has on insect community composition may be particularly relevant for the biological control of invasive grasses, due to the intensity of disturbance of grasslands worldwide.

KEYWORDS:

• Mowing
• native-range surveys
• Poaceae
• specialisation-disturbance hypothesis
• Sporobolus
• Tetramesa

Acknowledgements

We thank Pippa Muskett for invaluable assistance in the field and Clarke van Steenderen for assisting with lab work. Funding was provided by AgriFutures Australia, the Australian Government under their Rural Research and Development for Profit programme and the Queensland Department of Agriculture and Fisheries. Part of the funding for this work was provided by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation of South Africa. Any opinion, finding, conclusion or recommendation expressed in this material is that of the authors and the NRF does not accept any liability in this regard. Funding was also provided by the Working for Water (WfW) programme of the Department of Environmental Affairs: Natural Resource Management programme (DEA: NRM). Rhodes University is thanked for logistical support.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Agrifutures Australia, the Australian Government under their Rural Research and Development for Profit programme and the Queensland Department of Agriculture and Fisheries. Part of the funding for this work was provided by the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation of South Africa, Funding was also provided by the Working for Water (WfW) programme of the Department of Environmental Affairs: Natural Resource Management programme (DEA: NRM).