Mating disruption in Scaphoideus titanus Ball (Hemiptera: Cicadellidae) by vibrational signals

Conventional pesticides have detrimental effects on the global health and a development of environmentally friendly alternatives to control agricultural pests is essential. Mating disruption is an example of such method, since it exploits the natural airborne pheromone plumes that females emit to attract males. When a synthetic pheromone is applied to a field, males are disorientated and mating is prevented in the treated area. However, not all insect species communicate with olfactory signals. It has been estimated that 150 000 species use vibrations to achieve mating and among them there are several pests and important vectors of plant diseases. To control such species, growers may need to apply large amounts of pesticides, which is both environmentally and economically costly. The main goal of the present thesis was therefore to develop a vibrational mating disruption strategy. For this, the leafhopper Scaphoideus titanus was chosen as model species, since it uses vibrations both for mating and rivalry, along with being an economically important vector of the severe phytoplasma grapevine disease Flavescence doreé. Besides experiments concerning the proper mating disruption, laboratorial studies were made on signal transmission through grapevine tissues and on the ability of males and females to emit and receive substrate-borne signals. For the first time, it was shown that substrate-borne vibrational signals can allow communication between individuals despite lack of substrate continuity. This is an important contribution for an improved knowledge of the subject, but also to consider for control of insects that are distributed on closely adjacent plants like grapevine. Moreover, it was shown that males 3 are able to make directional decisions towards females and that there is an increased level of female signal intensity that triggers the male to initiate courtship. Pair formation in S. titanus starts with identification and proceeds with a location (search) stage before the final courtship. In the identification duets, male pulses were delayed after female reply, while they were fully synchronized during location and courtship duets. It is possible that mating disruption with vibrations is more successfully applied during the identification stage when external interferences could result in loss of important information that is needed to correctly identify the mating partner. Finally, during the mating disruption experiments, a pre-recorded natural rivalry signal of S. titanus was used for disruption when transmitted via grapevine wires to plants, where it masked the communication between males and females. In both semi-field and field experiments, the number of mated females was significantly reduced in presence of disruptive signal while females were mated in the silent control plants. These results suggest that vibrational mating disruption may have an important impact on future integrated pest managements of agricultural productions. Moreover, it is possible that the method can be applied to control different vibrational communicating pests. Vibrating plants in greenhouses may be easier than in an open field due to the protected environment and presence of energetic source. Yet, although the results from this thesis have shown that the principle of the method is promising, a future goal will first be to optimize the energetic and economic expenses of the system.