Vibrational playbacks and microscopy to study the signalling behaviour and female physiology of Philaenus spumarius

The meadow spittlebug Philaenus spumarius, vector of the bacterium Xylella fastidiosa, relies on vibrational communication to accomplish mating: the female calls to establish a duet with a male. A deeper knowledge of the species’ reproductive biology and behaviour would provide useful information for developing control techniques based on principles of ‘biotremology’, which studies the vibrational behaviour of animals. Playback tests were conducted on single females and male–female pairs of P. spumarius from June to October 2018, and the features of the recorded calling signals were analysed using a wavelet decomposition. Dissections were performed on females to evaluate the relationship between calling activity and ovarioles development. From August onwards, females started to emit calling signals and to develop ovarioles. Female calling activity, duration of their chirps and their responsiveness to mating increased as the season progressed, and they were correlated with ovarioles’ development and presence of mature eggs. Hence, the ovarian maturation represents a key factor in association with the development of the sexual behaviour of P. spumarius females. Conversely, males produced advertisement signals soon after adult eclosion in May, but these signals were not involved in the pair formation process. Mating was achieved only when males produced courtship signals in response to female calling signals and established with them vibrational duets starting from August. Here, we provide new information regarding the P. spumarius’ ethology and hypothesize that potential mating disruption techniques should consider the insect physiology and be applied when both sexes are responsive to mating signals.     

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.     

Mating interference of glassy‐winged sharpshooters,Homalodisca vitripennis

Animal communication is a complex behavior that is influenced by abiotic and biotic factors of the environment. Glassy‐winged sharpshooters (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), primarily use vibrational signaling for courtship communication. Because GWSS is a major pest, transmitting the plant pathogenic bacterium Xylella fastidiosa Wells et al., interruption of communication is a possible avenue for control. Playback of white noise, pre‐recorded female signals, and artificial female noise (continuously overlapping female signals) significantly reduced mating of GWSS when compared to silent control mating trials. Furthermore, to begin to determine the mechanism underlying playback control, female signaling activity was recorded in the presence of stimuli. In response to playback of female signals, females signaled (duet‐like) more often than females tested in the absence of playback. After the first playback, almost two‐thirds of females signaled a response within 3 s. Additionally, one‐third of the females signaled within 1 s after cessation of white noise, and significantly more in the time periods following noise termination. Results highlight how GWSS responds to differing competitive disturbances in the environment and lays important ground work that possibly could be used to develop pesticide‐free control methods.     

Melodic males and flashy females: Geographic variation in male and female reproductive behavior in red‐eyed treefrogs (Agalychnis callidryas)

Geographic variation in courtship behavior can affect reproductive success of divergent phenotypes via mate choice. Over time, this can lead to reproductive isolation and ultimately to speciation. The Neotropical red‐eyed treefrog (Agalychnis callidryas) exhibits high levels of phenotypic variation among populations in Costa Rica and Panama, including differences in color pattern, body size, and skin peptides. To test the extent of behavioral premating isolation among differentiated populations, we quantified male advertisement calls from six sites and female responses to male stimuli (acoustic and visual signals) from four sites. Our results show that both male advertisement calls and female behavior vary among populations: Discriminant function analyses can predict the population of origin for 99.3% ± 0.7 of males based on male call (dominant frequency and bandwidth) and 76.1% ± 6.6 of females based on female response behavior (frequency and duration of visual displays). Further, female mate choice trials (n = 69) showed that population divergence in male signals is coupled with female preference for local male stimuli. Combined, these results suggest that evolved differences among populations in male call properties and female response signals could have consequences for reproductive isolation. Finally, population variation in male and female behavior was not well explained by geographic or genetic distance, indicating a role for localized selection and/or drift. The interplay between male courtship and female responses may facilitate the evolution of local variants in courtship style, thus accelerating premating isolation via assortative mating.     

Male-male behavior and sexual dimorphism of the ear of a zaprochiline tettigoniid (Orthoptera: Tettigoniidae)

The external anatomy of the auditory system of an undescribed zaprochiline tettigoniid (Genus nov. 22 Sp. 1, Australian National Insect Collection, Canberra) shows sexual dimorphism: the male appears to have no auditory spiracle equivalent to that seen in the female. Nocturnally active males aggregate around female required nectar sources in a random manner with regard to each other. There is limited evidence, either from song interaction or from their behavior in the field, that males respond to each other by acoustic cues. Laboratory trials, testing male phonotaxis, showed that movement was random with respect to a target group of caged calling males. In the field, the only signs of agonistic behavior consisted of an increased calling rate when males were close together. Taken together, these data suggest that the male may not preceive sound in the same way as the female.     

Ontogenetic colour change signals sexual maturity in a non-territorial damselfly

Conspicuous colouration increases male reproductive success through female preferences and/or male–male competition. Despite the advantages of conspicuous colouration, inconspicuous male morphs can exist simultaneously in a population due to genetic diversity, condition dependence or developmental constraints. We are interested in explaining the male dichromatism in Xanthagrion erythroneurum damselflies. We reared these damselflies in outdoor insectaries under natural conditions and showed that this species undergoes ontogenetic colour changes. The younger males are yellow and change colour to red 6–7 days after their emergence. We took red and yellow male reflectance spectra and found that red males are brighter than yellow males. Next, we aimed to determine whether ontogenetic colour change signals sexual maturity with field observations and laboratory experiments. Our field observational data showed that red males are in higher abundance in the breeding territory, and they have a higher mating frequency than yellow males. We confirmed these field observations by enclosing a red and a yellow male with two females and found that yellow males do not mate in presence of red males. To determine whether colour change signals sexual maturity, we measured mating success of males before and after colour changes by enclosing a single male at different age (day 3-day 7) and colour (yellow, intermediate and red) with a single female in a mating cage. Males did not mate when yellow but the same male mated after it changed colour to red, suggesting the ontogenetic colour change signals sexual maturity in this species. Our study shows that male dichromatism can be age-dependent and ontogenetic colour change can signal age and sexual readiness in non-territorial insects.     

Females prefer males producing a high-rate song with shorter timbal–stridulatory sound intervals in a cicada species

Uncovering mate choice and factors that lead to the choice are very important to understanding sexual selection in evolutionary change. Cicadas are known for their loud sounds produced by males using the timbals. However, males in certain cicada species emit 2 kinds of sounds using respectively timbals and stridulatory organs, and females may produce their own sounds to respond to males. What has never been considered is the mate choice in such cicada species. Here, we investigate the sexual selection and potential impact of predation pressure on mate choice in the cicada Subpsaltria yangi Chen. It possesses stridulatory sound-producing organs in both sexes in addition to the timbals in males. Results show that males producing calling songs with shorter timbal–stridulatory sound intervals and a higher call rate achieved greater mating success. No morphological traits were found to be correlated with mating success in both sexes, suggesting neither males nor females display mate preference for the opposite sex based on morphological traits. Males do not discriminate among responding females during mate searching, which may be due to the high energy costs associated with their unusual mate-seeking activity and the male-biased predation pressure. Females generally mate once but a minority of them re-mated after oviposition which, combined with the desirable acoustic traits of males, suggest females may maximize their reproductive success by choosing a high-quality male in the first place. This study contributes to our understanding mechanisms of sexual selection in cicadas and other insects suffering selective pressure from predators.     

Female Reproductive Cycle and Sexual Conflict over Precopulatory Mate-guarding in Thermosphaeroma (Crustacea, Isopoda)

In species with time-limited opportunities for insemination, precopulatory mate-guarding is expected to coevolve with the duration of female reproductive cycles. Despite this adaptation to female characteristics, it may also be advantageous for males to adjust the duration of guarding with respect to sex ratio because the benefits of guarding are dependent on the availability of females. If female fitness is reduced because of guarding, male guarding behavior leads to intersexual conflict. We studied these aspects of male mate-guarding behavior in two closely related, thermal-spring isopods (Thermosphaeroma). First, guarding duration showed species specificity which was related to the duration of reproductive cycle; cycle length for females and duration of guarding by males in T. milleri were twice as long as in T. thermophilum. Second, males in both species adjusted their guarding duration with sex ratio, guarding longer when a competing male was present. Third, in T. thermophilum, ovarian development began immediately after the birth of the previous brood and continued through guarding, sexual molt and post-molt periods until oviposition, whereas in T. milleri, ovarian development was largely postponed until the post-molt period. Because guarding during ovary provisioning periods may be costly for females, we tested the existence of intersexual conflict over guarding duration in T. thermophilum. We compared the duration of guarding of control pairs with those of pairs in which either male guarding ability or female ability to resist guarding was reduced experimentally. Guarding durations for manipulated and control males were equal, but manipulated females were guarded longer, suggesting that conflict exists and that females can effectively shorten guarding duration by their behavior. Moreover, we suggest that selection in the context of intersexual conflict may play an important role in the evolution of delayed oviposition and sperm-storage organs in mate-guarding crustaceans.     

Genetic architecture of sensory exploitation: QTL mapping of female and male receiver traits in an acoustic moth

The evolution of extravagant sexual traits by sensory exploitation occurs if males incidentally evolve features that stimulate females owing to a pre‐existing environmental response that arose in the context of natural selection. The sensory exploitation process is thus expected to leave a specific genetic imprint, a pleiotropic control of the original environmental response and the novel sexual response in females. However, females may be subsequently selected to improve their discrimination of environmental and sexual stimuli. Accordingly, responses may have diverged and the original genetic architecture may have been modified. These possibilities may be considered by studying the genetic architecture of responses to male signals and to the environmental stimuli that were purportedly ‘exploited’ by those signals. However, no previous study has addressed the genetic control of sensory exploitation. We investigated this question in an acoustic pyralid moth, Achroia grisella, in which a male ultrasonic song attracts females and perception of ultrasound likely arose in the context of detecting predatory bats. We examined the genetic architecture of female response to bat echolocation signals and to male song via a cartographic study of quantitative trait loci (QTL) influencing these receiver traits. We found several QTL for both traits, but none of them were colocalized on the same chromosomes. These results indicate that – to the extent to which male A. grisella song originated by the process of sensory exploitation – some modification of the female responses occurred since the origin of the male signal.     

Limited flexibility in female Pacific field cricket (Teleogryllus oceanicus) exploratory behaviors in response to perceived social environment

How populations adapt, or not, to rapid evolution of sexual signals has important implications for population viability, but is difficult to assess due to the paucity of examples of sexual signals evolving in real time. In Hawaiian populations of the Pacific field cricket (Teleogryllus oceanicus), selection from a deadly parasitoid fly has driven the rapid loss of a male acoustic signal, calling song, that females use to locate and evaluate potential mates. In this newly quiet environment where many males are obligately silent, how do phonotactic females find mates? Previous work has shown that the acoustic rearing environment (presence or absence of male calling song) during late juvenile stages and early adulthood exposes adaptive flexibility in locomotor behaviors of males, as well as mating behaviors in both sexes that helps facilitate the spread of silent (flatwing) males. Here, we tested whether females also show acoustically induced plasticity in walking behaviors using laboratory‐reared populations of T. oceanicus from Kauai (HI; >90% flatwings), Oahu (HI; ~50% flatwings), and Mangaia (Cook Islands; no flatwings or parasitoid fly). Though we predicted that females reared without song exposure would increase walking behaviors to facilitate mate localization when song is rare, we discovered that, unlike males, female T. oceanicus showed relatively little plasticity in exploratory behaviors in response to an acoustic rearing environment. Across all three populations, exposure to male calling song during development did not affect latency to begin walking, distance walked, or general activity of female crickets. However, females reared in the absence of song walked slower and showed a marginally non‐significant tendency to walk for longer durations of time in a novel environment than those reared in the presence of song. Overall, plasticity in female walking behaviors appears unlikely to have facilitated sexual signal loss in this species.     

Plant architecture affects periodical cicada oviposition behavior on native and non‐native hosts

Variation in plant quality provides a basis for oviposition site selection for a variety of insects. Of the plant traits that influence plant–insect interactions, plant architecture has received little attention despite its putative role in modulating oviposition behavior. In a common garden comprised of native and non‐native plant species, we assessed how host plant architecture and identity influenced the oviposition behavior of 17‐year periodical cicadas (Homoptera: Cicadidae: Magicicada). On each host, we quantified the availability of branches suitable for oviposition and compared those measures with the branches used by ovipositing cicadas. Using this approach, we determined how the structural attributes of plants (i.e. branch diameter, length and incline) affected oviposition site selection. We then related cicada oviposition preferences to offspring performance by quantifying egg hatching success. On each host species, cicadas selectively used broader and longer branches for oviposition, suggesting that branch architecture provides a basis for oviposition behavior irrespective of plant identity. Broader and longer branches were more abundant on native than on non‐native hosts in our study, contributing to greater oviposition loads among the native species. Egg hatching success was similar among native and non‐native hosts. However, it is possible that the use of native plants for oviposition could enhance offspring output because native hosts generally contained more viable eggs per egg nest and more egg nests per plant. While previous accounts of cicada oviposition preferences have focused on differences in oviposition loads among hosts, our evaluation of within‐host branch selection by ovipositing cicadas helps to clarify oviposition preferences at a higher resolution and demonstrates that plant architecture provides an important basis for oviposition behavior. Furthermore, because branch structure can differ substantially among host species, our results suggest that periodical cicadas may be sensitive to the changes in plant composition that often result from non‐native plant invasions.     

Sex‐specific responses to territorial intrusions in a communication network: Evidence from radio‐tagged great tits

Signals play a key role in the ecology and evolution of animal populations, influencing processes such as sexual selection and conflict resolution. In many species, sexually selected signals have a dual function: attracting mates and repelling rivals. Yet, to what extent males and females under natural conditions differentially respond to such signals remains poorly understood, due to a lack of field studies that simultaneously track both sexes. Using a novel spatial tracking system, we tested whether or not the spatial behavior of male and female great tits (Parus major) changes in relation to the vocal response of a territorial male neighbor to an intruder. We tracked the spatial behavior of male and female great tits (N = 44), 1 hr before and 1 hr after simulating territory intrusions, employing automatized Encounternet radio‐tracking technology. We recorded the spatial and vocal response of the challenged males and quantified attraction and repulsion of neighboring males and females to the intrusion site. We additionally quantified the direct proximity network of the challenged male. The strength of a male's vocal response to an intruder induced sex‐dependent movements in the neighborhood, via female attraction and male repulsion. Stronger vocal responders were older and in better body condition. The proximity networks of the male vocal responders, including the number of sex‐dependent connections and average time spent with connections, however, did not change directly following the intrusion. The effects on neighbor movements suggest that the strength of a male's vocal response can provide relevant social information to both the males and the females in the neighborhood, resulting in both sexes adjusting their spatial behavior in contrasting ways, while the social proximity network remained stable. This study underlines the importance of “silent” eavesdroppers within communication networks for studying the dual functioning and evolution of sexually selected signals.     

A field cage study of the optimal age for release of radio-sterilized Aedes albopictus mosquitoes in a sterile insect technique program

The use of the sterile insect technique (SIT) is being considered as an additional tool for the control of Aedes albopictus (Skuse) (Diptera: Culicidae), the vector of Chikungunya and Dengue viruses in Mauritius. The aim of this study was to assess the competitiveness value of sterile males of different age and under various release conditions. Three release ratios were tested with sterile males of either 1, 3, or 5 days old at release. The competition of sterile males against same age or a mixed age population of fertile males (which is more representative of the field situation) was also investigated. The participation in mating (observed through single female oviposition), the average-induced sterility, and the male competitiveness index indicated that 3-day-old sterile males have the best balance between survival and mating capacity, and should therefore be the favored age of release in the field. Reduction in the cage fertility was obtained at 5-to-1 release ratio; however, it is speculated that at least a 10-fold ratio of sterile-to-fertile males should be chosen to induce substantial sterility in the wild Ae. albopictus population in the SIT pilot release site in Mauritius. Interestingly, this study showed for the first time that the age of the fertile male population against which the sterile males compete is a very important parameter that can significantly affect the sexual performance of sterile males, leading to overestimation of their competitiveness values.     

Non‐Conceptive Sexual Behavior in Spiders: A Form of Play Associated with Body Condition,Personality Type,and Male Intrasexual Selection

In the socially polymorphic spider Anelosimus studiosus, males mature early in the reproductive season and recruit to the webs of juvenile females and guard them until they mature. During the period before females mature, males and females engage in repeated bouts of non‐conceptive (play) sexual behavior, where the pair courts and engages in mock copulation; both males and females gain performance‐enhancing experience via these encounters. In this study, we examined the factors that underlie individual variation in the tendency to engage in non‐conceptive mating and determine whether it impacts male–male competition for females. We found that docile females, being less resistant to mating in general, are more likely to accept male courtship and non‐conceptive copulation as juveniles. Personality type influenced the exhibition of non‐conceptive sexual behavior in males as well. High body condition males of the aggressive phenotype were more likely to engage in non‐conceptive sexual behavior than males with lower body condition. Body condition did not influence docile males’ propensity to engage in non‐conceptive sexual behavior, but female size did. Docile males engaged in more non‐conceptive sexual displays with larger females. Engaging in non‐conceptive sexual displays negatively impacted male performance in staged male–male contests for access to females. This cost was greatest for males of the aggressive phenotype, which are otherwise favored in male–male contests. Our findings indicate expression of non‐conceptive sexual displays is linked to personality and results in reproductive performance trade‐offs for male A. studiosus.     

Mate choice in field crickets: can females acoustically detect male body size?

Females can potentially choose high-quality males by evaluating male secondary sexual traits such as acoustic signals. In field crickets (Orthoptera: Gryllidae), body size is thought to indicate male quality. Song carrier frequency (FQ) has been suggested to indicate male body size because the areas of the wing that control FQ (harp) scale with body size. However, no direct evidence showing that males can advertise their size via FQ exists for grylline crickets. Firstly, we show the lack of evidence indicating a clear relationship between FQ and body size for grylline crickets by conducting a literature review. We then calculate the three-way relationship between body size, harp size and FQ and show no relationship between FQ and body size for Gryllus bimaculatus. Eight other commonly measured song parameters also failed to indicate body size. Individual female preference functions for FQ are calculated and we demonstrate that females cannot select large males on the basis of FQ. Furthermore, we demonstrate that variation in male FQ falls within the range of female preference at the population level. Females probably cannot evaluate male body size based on the temporal and spectral properties of male calling song and alternative avenues of study are suggested.     

Stridulatory Sound-Production and Its Function in Females of the Cicada Subpsaltria yangi

Acoustic behavior plays a crucial role in many aspects of cicada biology, such as reproduction and intrasexual competition. Although female sound production has been reported in some cicada species, acoustic behavior of female cicadas has received little attention. In cicada Subpsaltria yangi, the females possess a pair of unusually well-developed stridulatory organs. Here, sound production and its function in females of this remarkable cicada species were investigated. We revealed that the females could produce sounds by stridulatory mechanism during pair formation, and the sounds were able to elicit both acoustic and phonotactic responses from males. In addition, the forewings would strike the body during performing stridulatory sound-producing movements, which generated impact sounds. Acoustic playback experiments indicated that the impact sounds played no role in the behavioral context of pair formation. This study provides the first experimental evidence that females of a cicada species can generate sounds by stridulatory mechanism. We anticipate that our results will promote acoustic studies on females of other cicada species which also possess stridulatory system.     

Sexual signal loss,pleiotropy, and maintenance of a male reproductive polymorphism in crickets

Pleiotropy between male signals and female preferences can facilitate evolution of sexual communication by maintaining coordination between the sexes. Alternatively, it can favor variation in the mating system, such as a reproductive polymorphism. It is unknown how common either of these scenarios is in nature. In Pacific field crickets (Teleogryllus oceanicus) on Kauai, Hawaii, a mutation (flatwing) that segregates as a single locus is responsible for the rapid loss of song production in males. We used outbred cricket colonies fixed for male wing morph to investigate whether homozygous flatwing and normal-wing (wild-type) females differ in responsiveness to male calling song and propensity to mate when paired with either a flatwing or normal-wing male in the presence or absence of courtship song. Flatwing females were less likely to mount a male than normal-wing females. Females of both genotypes showed a preference for normal-wing males and were more likely to mate in the presence of courtship song; normal-wing females were particularly likely to mate with song. Our results show that negative pleiotropy between obligate male silence and female mating behavior can constrain the evolution of sexual signal loss and contribute to the maintenance of a male reproductive polymorphism in the wild.     

Acoustic courtship communication inSyntomeida epilais Wlk. (Lepidoptera: Arctiidae,Ctenuchinae)

The polka-dot wasp moth,Syntomedia epilais Wlk. (Lepidoptera, Arctiidae, Ctenuchinae), engages in extensive acoustic signaling during courtship. The signals, which are produced by both sexes, consist of sexually dimorphic trains of ultrasonic clicks. Field and laboratory behavioral experiments demonstrated that (1) sound production from both the male and the female is required for mating success, (2) femaleS. epilais show a higher level of acoustic responsiveness to male acoustic signals than to female signals, and (3) males use the female acoustic signals to locate their potential mates. It is suggested that the existence of the system is made possible by a reduction in bat predation pressure, perhaps the result of extreme distastefulness combined with the distinctive acoustic image that flying ctenuchines present to foraging bats.     

Territoriality and fighting in a colonial thrips, Hoplothrips pedicularius, and sexual dimorphism in Thysanoptera

ABSTRACT.

• 1 Hoplothrips pedicularius (Haliday) (Thysanoptera: Phlaeothripidae), a tubuliferan thrips in which males possess greatly enlarged forelegs, lives in colonies on Stereum fungus.
• 2 Females oviposit onto communal egg masses, and males fight by grasping and stabbing with their forelegs in territorial defence of oviposition areas. Prolonged escalated fights occur between males who are of similar size.
• 3 Larger males usually win fights and become dominant at the oviposition area. Dominant males secure 80% of matings, and mate most frequently during oviposition periods, with an ovipositing female.
• 4 Smaller, subordinate males avoid fights and attempt to 'sneak’copulations. However, they occasionally challenge the dominant male. Challenges tend to follow copulations by the subordinate male and occur more frequently between males who are of similar size.
• 5 Subordinate males who eventually leave the oviposition area are larger than those who remain, have frequently challenged the dominant male, and have more frequently been stabbed.
• 6 Sexual dimorphism in thrips is associated with gregariousness, claustral habitats, female-biased sex ratios, and male winglessness. In thrips genera in which males exhibit foreleg armature, males are larger relative to females. The ecological circumstances promoting sexual dimorphism and male fighting in spatially-structured populations are discussed.