Dr Lena Grinsted– University of Portsmouth
Dr Alan Stewart – University of Sussex
Biological pest control is key to sustainable solutions for intensive agriculture.
Spiders can provide effective pest control in the right circumstances, but their effectiveness is usually limited because most species are generalist predators that will engage in intra-guild predation, including cannibalism, when present at high densities.
This study aims to test the hypothesis that group living spiders are uniquely suited for pest control because of their unusually high tolerance of conspecifics and avoidance of cannibalism.
The group living spider, Cyrtophora citricola, occurs naturally on prickly pear cacti (Opuntia spp.) borders around agricultural fields in southern Spain. Here they can cover the cacti in dense webbing that functions as a substrate for other predators and parasites such as a klepto-parasitic spider, Argyrodes argyrodes, and a generalist predator, Holocnemus pluchei. The large webbing intercepts, and may help to control, a variety of flying insects such as the moth Tuta absoluta that has recently become a serious pest of tomato crops across Europe. However, webs may also capture important crop pollinators, such as bees.
Understanding trophic and behavioural interactions within this community of predators, parasites and prey is crucial to assess the ability of group living spiders to provide pest control, and to understand the optimal species composition within colonies for providing this ecosystem service. The transparent web structures of C. citricola provide a rare and ideal platform on which to observe and manipulate these interactions.
The project will consist of:
1) Field experiments in southern Spain where the relative abundance of H. pluchei and A. argyrodes in spider colonies will be manipulated to explore how community structure and composition affects the fitness of C. citricola and its ability to capture pests and pollinators;
2) Controlled, lab-based experiments where the effectiveness of C. citricola to capture and control T. absoluta will be evaluated.