Using acoustic technology to reduce bark beetle reproduction

A multidimensional framework to quantify the effects of urbanization on avian breeding fitness

Urbanization has dramatically altered Earth's landscapes and changed a multitude of environmental factors. This has resulted in intense land-use change, and adverse consequences such as the urban heat island effect (UHI), noise pollution, and artificial light at night (ALAN). However, there is a lack of research on the combined effects of these environmental factors on life-history traits and fitness, and on how these interactions shape food resources and drive patterns of species persistence. Here, we systematically reviewed the literature and created a comprehensive framework of the mechanistic pathways by which urbanization affects fitness and thus favors certain species. We found that urbanization-induced changes in urban vegetation, habitat quality, spring temperature, resource availability, acoustic environment, nighttime light, and species behaviors (e.g., laying, foraging, and communicating) influence breeding choices, optimal time windows that reduce phenological mismatch, and breeding success. Insectivorous and omnivorous species that are especially sensitive to temperature often experience advanced laying behaviors and smaller clutch sizes in urban areas. By contrast, some granivorous and omnivorous species experience little difference in clutch size and number of fledglings because urban areas make it easier to access anthropogenic food resources and to avoid predation. Furthermore, the interactive effect of land-use change and UHI on species could be synergistic in locations where habitat loss and fragmentation are greatest and when extreme-hot weather events take place in urban areas. However, in some instances, UHI may mitigate the impact of land-use changes at local scales and provide suitable breeding conditions by shifting the environment to be more favorable for species' thermal limits and by extending the time window in which food resources are available in urban areas. As a result, we determined five broad directions for further research to highlight that urbanization provides a great opportunity to study environmental filtering processes and population dynamics.

Pinyon Engraver Beetle Acoustics: Stridulation Apparatus, Sound Production and Behavioral Response to Vibroacoustic Treatments in Logs

Simple Summary

Acoustic technology is a potential tool to protect wood materials and live trees from colonization by bark beetles and other wood-infesting insects. Bark beetles such as the pinyon engraver beetle Ips confusus use chemical and acoustic cues to communicate and to locate potential mates in trees. In this study, we describe the structures and airborne sounds produced by the pinyon engraver beetle, and test the efficacy of vibroacoustic treatments for tree protection against this beetle. Only female beetles possessed sound producing structures, located on the back of the head and inside the thorax. We analyzed and described the airborne sounds, called chirps, produced by females when held by tweezers or placed on their back. We tested a wide variety of vibroacoustic treatments played into logs but these sound treatments did not prevent male entry into logs and did not disrupt female–male interactions, female tunneling behavior, reproduction or egg laying. We suggest further studies if acoustic methods are to be utilized to control this bark beetle.

Abstract

Bark beetles are among the most influential biotic agents in conifer forests, and forest management often focuses on bark beetle chemical communication for tree protection. Although acoustic communication occurs in many bark beetle species, we have yet to utilize acoustic communication for bark beetle control. Here, we describe the stridulatory organs and ‘stress’ chirps of the pinyon engraver, Ips confusus, a significant pest and mortality agent of pinyon pine in western North America. Only females possessed stridulatory organs and their stress chirps varied significantly in duration, pulses per chirp, and dominant frequency. We tested an array of acoustic-vibrational treatments into logs but were unable to disrupt male entry into logs or alter female–male interactions, female tunneling, and female oviposition. We found acoustic–vibrational treatments had little effect on I. confusus behavior and suggest further studies if acoustic methods are to be utilized for bark beetle control.

Physical contact, volatiles, and acoustic signals contribute to monogamy in an invasive aggregating bark beetle

The behavioral strategies and mechanisms by which some insects maintain monogamous mating systems are not well understood. We investigated the mating system of the bark beetle Dendroctonus valens, and identified several contributing mechanisms. Field and laboratory observations suggest the adults commonly form permanent bonds during host colonization. Moreover, it showed mated females that remained paired with males produced more offspring than mated females that were alone in galleries. In bioassays, a second female commonly entered a gallery constructed by a prior female. Videos show she commonly reached the location of the first female, but they did not engage in actual fighting. Rather, the second female typically departs to form her own gallery. Acoustic signaling likewise does not appear to influence female-female encounters, based on controlled muting experiments. Instead, the intruder appears to perceive the resident's presence by physical contact. Both acoustic signals and volatiles released by females during gallery constructing were shown to attract males. After a male joined a female in a gallery, the male-produced aggressive sounds, which were shown by playback to deter other males from entering the gallery. Unlike female-female interactions, resident males use their head and rear to push intruders out of galleries. Additionally, volatiles released by males during feeding repelled intruding males, discouraging them from entering the gallery. Males also construct plugs that block the entrance, which may prevent subsequent males and predators from entering the gallery. Thus, D. valens has evolved multifaceted mechanisms contributing to single pairings that confer benefits to both sexes.

Effects of Diaphorina citri Population Density on Daily Timing of Vibrational Communication Calls: Potential Benefits in Finding Forage

Adult Diaphorina citri (ACP) use visual and chemical cues to locate young citrus flush shoots on which they forage and oviposit, and they use vibrational communication duetting calls as cues to help locate mates. For individual pairs, calling and mating usually peaks between 10:00 and 15:00. To explore whether call rates (calls/h) are affected by interactions with nearby conspecifics, rates were compared in small citrus trees on which either 5 or 25 ACP female and male pairs had been released at 17:00 for later recording from sunrise (06:00) to 22:00. Final ACP locations were noted 40 h after release. Call rates were similar in both treatments during normal mating hours. However, rates were significantly higher for low- than high-density treatments between 06:00 and 10:00, which suggests calling during this period may be affected by conspecific density. Both sexes aggregated on flush at both densities. We discuss the potential that ACP producing calls near sunrise, outside of normal mating hours, might benefit from gains in reproductive fitness in low-density contexts if they call not only to locate mates but also to locate preferred flush—in which case, co-opting of vibrations to disrupt both mating and foraging may be feasible.

Anthropogenic noise and the bioacoustics of terrestrial invertebrates

Anthropogenic noise is an important issue of environmental concern owing to its wide-ranging effects on the physiology, behavior and ecology of animals. To date, research has focused on the impacts of far-field airborne noise (i.e. pressure waves) on vertebrates, with few exceptions. However, invertebrates and the other acoustic modalities they rely on, primarily near-field airborne and substrate-borne sound (i.e. particle motion and vibrations, respectively) have received little attention. Here, we review the literature on the impacts of different types of anthropogenic noise (airborne far-field, airborne near-field, substrate-borne) on terrestrial invertebrates. Using literature on invertebrate bioacoustics, we propose a framework for understanding the potential impact of anthropogenic noise on invertebrates and outline predictions of possible constraints and adaptations for invertebrates in responding to anthropogenic noise. We argue that understanding the impacts of anthropogenic noise requires us to consider multiple modalities of sound and to cultivate a broader understanding of invertebrate bioacoustics.

Vibrational mating disruption of Empoasca vitis by natural or artificial disturbance noises

BACKGROUND

The green leafhopper, Empoasca vitis, is a polyphagous pest of grapevine and tea plants. To date population density is controlled primarily by insecticides and there is a demand for more sustainable controls. To develop a vibrational mating disruption method, the natural occurrence of a 'disruptive signal' was investigated. Further, the efficacy of natural and artificial 'disruptive signals' was determined.

RESULTS

With behavioral trials we described male rivalry and recorded a species-specific disruptive signal (DP). The DP, a single pulse overlapping the competitor male call, interfered with the rival's ability to locate the female. Laboratory playback disruption trials revealed that the pair formation process was prevented by artificial disturbance noises that included the following features: E. vitis DP, Scaphoideus titanus disturbance noise, and a pure tone (250 Hz). Among these, the pure tone was most efficient at preventing mating.

CONCLUSION

Results support development of a vibrational mating disruption method as a control strategy for E. vitis. To simultaneously disrupt the mating of E. vitis and S. titanus, the possibility of applying the S. titanus disturbance noise combined with the pure tone is discussed. © 2018 Society of Chemical Industry.

Disrupting Mating Behavior of Diaphorina citri (Liviidae)

Severe economic damage from citrus greening disease, caused by 'Candidatus Liberibacter asiaticus' bacteria, has stimulated development of methods to reduce mating and reproduction in populations of its insect vector, Diaphorina citri (Hemiptera: Liviidae). Male D. citri find mating partners by walking on host plants, intermittently producing vibrational calls that stimulate duetting replies by receptive females. The replies provide orientational feedback, assisting the search process. To test a hypothesis that D. citri mating can be disrupted using vibrational signals that compete with and/or mask female replies, courtship bioassays were conducted in citrus trees with or without interference from female reply mimics produced by a vibrating buzzer. Statistically significant reductions occurred in the rates and proportions of mating when the buzzer produced reply mimics within 0.4 s after male courtship calls compared with undisturbed controls. Observations of courtship behaviors in the two bioassays revealed activity patterns that likely contributed to the reductions. In both disruption and control tests, males reciprocated frequently between structural bifurcations and other transition points where signal amplitudes changed. Males in the disruption bioassay had to select among vibrational signals combined from the buzzer and the female at each transition point. They often turned towards the buzzer instead of the female. There was a statistically significant reduction in the proportion of males mating if they contacted the buzzer, possibly due to its higher vibration amplitude and duration in comparison with female replies. Potential applications of D. citri mating disruption technology in citrus groves are discussed.

Sound-Triggered Production of Antiaggregation Pheromone Limits Overcrowding of Dendroctonus valens Attacking Pine Trees

For insects that aggregate on host plants, both attraction and antiaggregation among conspecifics can be important mechanisms for overcoming host resistance and avoiding overcrowding, respectively. These mechanisms can involve multiple sensory modalities, such as sound and pheromones. We explored how acoustic and chemical signals are integrated by the bark beetle Dendroctonus valens to limit aggregation in China. In its native North American range, this insect conducts nonlethal attacks on weakened trees at very low densities, but in its introduced zone in China, it uses mixtures of host tree compounds and the pheromone component frontalin to mass attack healthy trees. We found that exo-brevicomin was produced by both female and male D. valens, and that this pheromone functioned as an antiaggregating signal. Moreover, beetles feeding in pairs or in masses were more likely than were beetles feeding alone to produce exo-brevicomin, suggesting a potential role of sound by neighboring beetles in stimulating exo-brevicomin production. Sound playback showed that an agreement sound was produced by both sexes when exposed to the aggregation pheromone frontalin and attracts males, and an aggressive sound was produced only by males behaving territorially. These signals triggered the release of exo-brevicomin by both females and males, indicating an interplay of chemical and sonic communication. This study demonstrates that the bark beetle D. valens uses sounds to regulate the production of an antiaggregation pheromone, which may provide new approaches to pest management of this invasive species.

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.

Use of acoustics to deter bark beetles from entering tree material

BACKGROUND

Acoustic technology is a potential tool to protect wood materials and eventually live trees from colonization by bark beetles. Bark beetles such as the southern pine beetle Dendroctonus frontalis, western pine beetle D. brevicomis and pine engraver Ips pini (Coleoptera: Curculionidae) use chemical and acoustic cues to communicate and to locate potential mates and host trees. In this study, the efficacy of sound treatments on D. frontalis, D. brevicomis and I. pini entry into tree materials was tested.

RESULTS

Acoustic treatments significantly influenced whether beetles entered pine logs in the laboratory. Playback of artificial sounds reduced D. brevicomis entry into logs, and playback of stress call sounds reduced D. frontalis entry into logs. Sound treatments had no effect on I. pini entry into logs.

CONCLUSION

The reduction in bark beetle entry into logs using particular acoustic treatments indicates that sound could be used as a viable management tool.

Technique for studying arthropod and microbial communities within tree tissues

Phloem tissues of pine are habitats for many thousands of organisms. Arthropods and microbes use phloem and cambium tissues to seek mates, lay eggs, rear young, feed, or hide from natural enemies or harsh environmental conditions outside of the tree. Organisms that persist within the phloem habitat are difficult to observe given their location under bark. We provide a technique to preserve intact phloem and prepare it for experimentation with invertebrates and microorganisms. The apparatus is called a ‘phloem sandwich’ and allows for the introduction and observation of arthropods, microbes, and other organisms. This technique has resulted in a better understanding of the feeding behaviors, life-history traits, reproduction, development, and interactions of organisms within tree phloem. The strengths of this technique include the use of inexpensive materials, variability in sandwich size, flexibility to re-open the sandwich or introduce multiple organisms through drilled holes, and the preservation and maintenance of phloem integrity. The phloem sandwich is an excellent educational tool for scientific discovery in both K-12 science courses and university research laboratories.