Valerio Mazzoni

Disruption of the reproductive behaviour of Scaphoideus titanus by playback of vibrational signals

Scaphoideus titanus Ball (Hemiptera: Cicadellidae: Deltocephalinae) is the vector of the grapevine disease Flavescence dorée. In S. titanus the male–female duet (MFD), based on species‐specific vibrational signals, is essential for successful copulation. The female reply within a duet is a single pulse that is coupled with the male pulse with constant latency. It has been shown that a rival male can interrupt an existing duet by emitting disruptive noise signals. We tested whether the reproductive behaviour of S. titanus can be disrupted by the playback of intra‐specific and synthesized vibrational signals. Tested males responded to the playback of an MFD with typical rivalry behaviour. Such behaviour includes silent search for a duetting female (satellite behaviour) and/or emission of disruptive signals. These signals were emitted either after exchange of male–female pulses or after two male pulses coupled by latency corresponding to the female response window. The onset of male disruptive signals overlapped with a female pulse. We suggest that the intruder’s disruptive signals can mask the female reply and confuse courting males. Playback of disruptive vibrational signals reduced the level of male calling and interrupted an established MFD that consequently resulted in a significantly reduced number of copulations. These results indicate that the vibrational communication channel is open to interference either from abiotic environmental noise or from signals produced by sexual competitors or heterospecifics. The present study also suggests that a detailed understanding of leafhopper behaviour is essential for trying new approaches in the development of more environmentally friendly control practices.

Exploitation of insect vibrational signals reveals a new method of pest management.

Food production is considered to be the main source of human impact on the environment and the concerns about detrimental effects of pesticides on biodiversity and human health are likely to lead to an increasingly restricted use of chemicals in agriculture. Since the first successful field trial, pheromone based mating disruption enabled sustainable insect control, which resulted in reduced levels of pesticide use. Organic farming is one of the fastest growing segments of agriculture and with the continuously growing public concern about use of pesticides, the main remaining challenge in increasing the safety of the global food production is to identify appropriate alternative mating disruption approaches for the numerous insect pests that do not rely on chemical communication. In the present study, we show for the first time that effective mating disruption based on substrate-borne vibrational signals can be achieved in the field. When disruptive vibrational signals were applied to grapevine plants through a supporting wire, mating frequency of the leafhopper pest Scaphoideus titanus dropped to 9 % in semi-field conditions and to 4 % in a mature vineyard. The underlying mechanism of this environmentally friendly pest-control tactic is a masking of the vibrational signals used in mate recognition and location. Because vibrational communication is widespread in insects, mating disruption using substrate vibrations can transform many open field and greenhouse based farming systems.

Effects of chlorantraniliprole on eggs and larvae of Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae)

BACKGROUND Chlorantraniliprole is a novel insecticide belonging to the class of selective ryanodine receptor agonists. The aims of this study were to evaluate the toxicity and the length of residual activity of chlorantraniliprole against the grapevine moth, Lobesia botrana (Denis & Schiffermüller), larvae and eggs, under laboratory and field conditions. RESULTS Dose-response bioassays showed that chlorantraniliprole had a high level of toxicity to neonate larvae of L. botrana. In field trials, chlorantraniliprole applied at 35 mg AI L(-1) was as effective against the larvae as the commercial standard reference, chlorpyrifos-ethyl, and had a long-lasting effect. When applied at a field rate of 35 mg AI L(-1), chlorantraniliprole caused greater than 20% egg mortality. The toxic effect of chlorantraniliprole is completed by its substantial activity against neonates emerging from eggs. CONCLUSION Chlorantraniliprole can be considered as a useful tool for L. botrana control, providing a new standard in efficacy and an extremely good residual control. The combined effects against eggs and larvae of grapevine moth should contribute to its efficacy in the field. The new mode of action of chlorantraniliprole and its safety to beneficials and non-target organisms would be extremely useful in IPM and for managing resistance to insecticides.

Inter-Plant Vibrational Communication in a Leafhopper Insect

Vibrational communication is one of the least understood channels of communication. Most studies have focused on the role of substrate-borne signals in insect mating behavior, where a male and a female establish a stereotyped duet that enables partner recognition and localization. While the effective communication range of substrate-borne signals may be up to several meters, it is generally accepted that insect vibrational communication is limited to a continuous substrate. Until now, interplant communication in absence of physical contact between plants has never been demonstrated in a vibrational communicating insect. With a laser vibrometer we investigated transmission of natural and played back vibrational signals of a grapevine leafhopper, Scaphoideus titanus, when being transmitted between leaves of different cuttings without physical contact. Partners established a vibrational duet up to 6 cm gap width between leaves. Ablation of the antennae showed that antennal mechanoreceptors are not essential in detection of mating signals. Our results demonstrate for the first time that substrate discontinuity does not impose a limitation on communication range of vibrational signals. We also suggest that the behavioral response may depend on the signal intensity.

Multiple lines of evidence for reproductive winter diapause in the invasive pest Drosophila suzukii: useful clues for control strategies

Successful management of invasive pests, such as Drosophila suzukii, relies on a fine understanding of their biology. Genomic and physiological studies have suggested that the invasive success of D. suzukii is strongly associated with its ability to overwinter in a reproductive diapause state. Here, we coupled field surveys with comparative morphology and genetics to increase our understanding of D. suzukii overwintering behavior and provide useful indications for its management. The results of a 4-year-long field trapping in an Italian mountain region indicate that D. suzukii is continuously captured during winter months and that the number of captures is correlated with temperature. Capture patterns are also contrasting between sexes: while females are more abundantly caught during winter and summer, males are more abundant in spring and autumn. We found that overwintering could occur not only in natural environments, such as woods, but also in anthropic shelters. Comparative morphology and genetics further indicate that spermathecae may play an important adaptive role during winter. Our results unveil complex winter biology in D. suzukii and highlight how the number of overwintering females is an earlier predictor of summer population size. We hence propose that in a given year infestation may be better forecasted by taking into account the captures of the previous winter. We recommend that control methods be diapause-aware. For instance, they should take place in late winter/early spring and close to natural environments, and not only in fruit ripening season and close to orchards.

Manipulating behaviour with substrate‐borne vibrations – potential for insect pest control

This review presents an overview of the potential use of substrate-borne vibrations for the purpose of achieving insect pest control in the context of integrated pest management. Although the importance of mechanical vibrations in the life of insects has been fairly well established, the effect of substrate-borne vibrations has historically been understudied, in contrast to sound sensu stricto. Consequently, the idea of using substrate-borne vibrations for pest control is still in its infancy. This review therefore focuses on the theoretical background, using it to highlight potential applications in a field environment, and lists the few preliminary studies that have been or are being performed. Conceptual similarities to the use of sound, as well as limitations inherent in this approach, are also noted.

Mating Behavior of Hyalesthes obsoletus (Hemiptera: Cixiidae)

ABSTRACT The mating behavior of Hyalesthes obsoletus Signoret (Hemiptera: Cixiidae) was studied to determine the role of substrate-borne vibrational signals in partner recognition, pair formation, and courtship. Planthopper vibrational signals were detected from nettle, Urtica dioica L., cuttings by laser vibrometer. Either male or female could initiate the mating sequence that was divided into three sections: recognition, courtship and precopula. The females were the more vibrationally active gender in the recognition stage and males in the courtship and precopula stages. Four distinct syllables constituted the male repertoire and were emitted in different behavioral contexts. The male syllable 1 was used during the recognition duet, as a reply to female pulse trains and it formed, in combination with male syllable 4, the male precopula signal. This latter signal was emitted in the vicinity of a receptive female and accompanied by jerky lateral movements of the body and tapping of the legs to the substrate. Although nonduetting males emitted long trains composed of male syllable 2, males during the courtship phase emitted trains formed mainly by male syllable 3. Female vibrational signals consisted of pulses, emitted either in trains during the recognition phase or as single pulses, in reply to male trains in the courtship stage. In the precopula phase, the females ceased signaling. According to our results, in H. obsoletus the vibrational signals play a major role in stimulating the male search process and in ensuring the female acceptance.

Active Space and the Role of Amplitude in Plant-Borne Vibrational Communication

Unlike airborne signals, substrate-borne vibrational signals are confined within the size and shape of their medium of communication, which in the case of small arthropods often coincides with the host plant. By following the substrate continuity, a vibrational signal creates a more or less complex active space network that enables communication between individuals. Due to the heterogeneity of plants, physical properties of the substrate can vary in the efficiency of signal transmission and in the diffusion of signals along the tissues. Under such circumstances, the identification and location of a potential partner may be a difficult task. Amplitude cues can be of great importance in orientation to the source of a vibrational signal by providing information about both direction and distance. As examples, we present two case studies on mating behavior of a leafhopper and a planthopper.

The process of pair formation mediated by substrate-borne vibrations in a small insect.

The ability to identify and locate conspecifics depends on reliable transfer of information between emitter and receiver. For a majority of plant-dwelling insects communicating with substrate-borne vibrations, localization of a potential partner may be a difficult task due to their small body size and complex transmission properties of plants. In the present study, we used the leafhopper Scaphoideus titanus as a model to investigate duetting and mate searching associated with pair formation. Studying these insects on a natural substrate, we showed that the spatio-temporal structure of a vibrational duet and the perceived intensity of partners signals influence the mating behaviour. Identification, localization and courtship stages were each characterized by a specific duet structure. In particular, the duet structure differed in synchronization between male and female pulses, which enables identification of the partner, while the switch between behavioural stages was associated with the male-perceived intensity of vibrational signals. This suggests that males obtain the information about their distance from the female and optimize their strategy accordingly. More broadly, our results show that even in insects smaller than 1cm, vibrational signals provide reliable information needed to find a mating partner.

Vibrational communication networks: eavesdropping and biotic noise

In nature, communication predominantly occurs in a group of several conspecific and/or heterospecific individuals within signaling and receiving range of each other, i.e., in a network environment. Vibrational communication in the context of sexual behavior has been, in the past, usually considered as a private communication channel, free of potential competitors and eavesdropping predators or parasitoids and consequently only rarely studied outside an emitter–receiver dyad. We provide an overview of work related to vibrational communication in the presence of (a) environmental (abiotic) noise, (b) other conspecific and/or heterospecific signalers (biotic noise), (c) rivals and (d) exploiters (predators and parasitoids). The evidence gathered in the last few years shows that arthropods relying on substrate-borne vibrations communicate within a rich and complex vibrational world and reveals diverse interactions and mechanisms. Considering vibrational communication from a network perspective may allow us in the future to identify sources of selection pressures that cannot be recognized in a communication dyad.