Biology session

In my TDK-research I studied non-consumptive interactions between the virus vector leafhopper Psammotettix alienus which is a dominant sap feeding pest in cereal fields, and the hunting spider Tibellus oblongus which is a dominant predator of arable fields, grassy field margins and meadows. In order to acquire nutrients, leafhoppers need to penetrate plant tissues with their mouthparts (stylet) and feed from phloem sap. To reach the phloem, leafhoppers need to pierce their stylet into the plant tissues. This process is called penetration. During penetrations, leafhoppers produce a so-called salivary sheath that helps penetrating plant tissues and which permanently remains there. The presence of the salivary sheaths clearly indicates penetration and feeding. During phloem ingestion, escaping capabilities of the leafhopper are reduced, thus feeding in the presence of a predator is a risk prone behaviour. This is likely to result in reduced nutrient uptake with its fitness consequences, and may also influence virus transmission by the vector.

We conducted laboratory experiments to show the effect of predator presence on the feeding behaviour of leafhoppers, quantified by the number of salivary sheaths. Trials were made in divided micro isolators, where a dividing mesh prevented actual predation by spiders, but made possible sensing the presence of each other. Each observation was run for 24 hours.

Results show that those leafhoppers which were under predator stress left fewer salivary sheaths than control animals. Thus generalist predators, like T. oblongus, contribute to biological control not only by direct predation effect, but also by their non-consumptive stress effect that decreases pest feeding success and potentially affects its virus vector potential.