The effects of elastic waves on biological objects elastic waves in nature, science, engineering, technology, medicine

Vibroreception. Numerous observations and electrophysiological data indicate the ability of insects to perceive substrate vibrations. Receptors responding to these vibrations are localized in the legs^* . By recording the total activity of sensory neurons in the foot nerves, it is possible to obtain an indication of the sensitivity of these receptors. The response threshold is the minimum amplitude of substrate displacement or acceleration at which responses are observed (Figure 2.16) [163].

1-Carabus, 2-Vespa, 3-Bombus, 4-Pyrantels, 5-Periplaneta, 6-Liogryllus.
Abscissa axis - frequency, Hz; ordinate axis - vibration amplitude, nm
Figure 2.16 - Frequency Threshold Characteristics of Foot Vibrators

As a result of a comparative study of a fairly large number of insect species, it was found that they can be roughly divided into two groups: high-sensitive and low-sensitive (Table 2.6). The former include cockroaches, spiders, hoverflies, hymenopterans, hard flies and others; the latter include semi-hard flies, bipterans and some hard flies. The differences between these groups relate not only to response thresholds, but also to optimal frequencies. In the first case, these are usually in the range 1-3 kHz, while in the second, they do not exceed 0.4 kHz.

Table 2.6 - Sensitivity of insects to vibrations.

Group	Types	Optimum frequency, kHz	Threshold amplitude, µm
I	Periplaneta americana	1,4	0,000004
	Decticus verrucivorus	2,0	0,000036
	Tachyucines asynamorus	1,0	0,000068
	Liogryluus campestris	1,5	0,0001
	Melolontha melolontha	1,8	0,0001
	Vanessa atalanta	3,0	0,00029
	Carausius sp	1,5	0,00035
	Satyridae	2,0	0,0004
	Geotrupes sylvaticus	1,5	0,00048
	Stenobothrus sp	3,0	0,00062
	Vanessa io	2,0	0,00068
	Aeschna cyanea	3,0	0,0009
	Apls mellifera	2,5	0,013
	Andrena nitida	1,0	0,018
	Camponotus sp.	2,0	0,019
	Forfikula auricularia	1,2	0,019
	Bombus soroensis	1,5	0,032
	Vespa crabro	1,5	0,036
	Pterostichus sp.	0,8	0,040
	Silpha obscura	1,0	0,045
	Agrotik sp.	1,2	0,057
	Pseudophonus sp.	0,75	0,061
II	Reduvius personatus	0,25	1,0
	Rhodnius prolixus	0,4	1,3
	Eristalis sp.	0,2	6,59
	Calliphora erithrocephala	0,3	17,4

Comparative anatomical materials and the results of extirpations of various foot receptors suggest that in sensitive species the perception of vibrations is predominantly carried out by subgenual organs, while in non-sensitive species by tibiogarsal chordotonal and trichoidal sensible on the feet. Such a pattern can be observed when comparing many groups of insects, but it still cannot be considered universal, because the absence of subgenera organ does not exclude sufficiently high sensitivity to vibrations (Melolontha, Geotrupes), and in its presence perception can be carried out mainly by other receptors. Accurate elucidation of the role of individual sensible or organs in this process is very difficult, so few reliable data have been obtained so far [163].

Similar results were obtained when studying the foot receptors of crickets (Gryllus). The optimum sensitivity of the subgenera organs of the forelegs ranged from 0.8-1 kHz and that of the hind legs from 0.4-0.5 kHz. Minimum thresholds (in amplitude of displacement) differed little in all three cases (1.4X10^-8 -2.2X10^-8 cm), but anterior receptors were less sensitive to acceleration. Artificial weighting of the hind legs had no effect on receptor function, so it can be assumed that their performance is determined only by the mechanical properties of the subgenera organs themselves. A comparison of the organs of the three pairs of legs shows that their optimal frequencies are inversely related to their own mass [163].
The above data are in accordance with model concepts, according to which the subgenera organ is considered as an elastic membrane with a mass in the center, stretched in a vessel with fluid. Shaking of such a system causes displacement of the mass and oscillation of the membrane recorded by the meter (sensilla).
In leaf-cutter ants (Atta), foot receptors respond to sounds in the range of 0.05-4 (7) kHz. The optimum of sensitivity in displacement amplitude lies in the region of 1-3 kHz (minimum threshold - 1.ZX10^-7 cm), and in acceleration - 0.1-2 kHz (threshold - 2.5 cm/s² ). The most sensitive sensible are located in the forelegs, with soldiers being less susceptible to vibration than workers. Selective disruption of the different receptors showed that mainly the campaniform sensible located at the acetabular and femoral articulation area responded to substrate vibrations. The role of the subgenera organs in this case remains unclear.
Vibrations perceived by insects in natural conditions are caused by abiotic factors (wind, rain, etc.) and by the activity of animals (including individuals of their own species). Usually shaking of the substrate occurs during movement, feeding, making passages, construction and other life activities. But in addition, many insects intentionally knock on the surrounding objects with various body parts or scratch them with their mandibles^* . In some cases, the substrate (e.g. dry leaves) serves only to amplify sound, while in others it is used as a communication channel, and the vibrations propagating in it serve as signals carrying certain information. Such communication is well developed in social insects (termites, ants, bees, wasps), as well as in Plecoptera, Psocoptera, Anobiidae and others. In solitary insects, these signals are used to attract individuals of the opposite sex. Termites knock on the walls of the nest in case of danger. The reproduction of these vibrations triggers a series of defensive reactions in them. Hungry wasp larvae get food if they scratch cell walls with their mandibles. Some ants (Atta, Megaponera), once under the soil layer, emit "distress signals" that attract the attention of individuals on the surface. The wood-dwelling species (Catnponotus) knock on the substrate when danger or damage to the nest occurs. Such signals play a very important role in the life of bees. The slightest shaking of the hive triggers an active defensive reaction. There is also evidence that queen bees respond to the "croaking" of other queens, or its imitation, only if the signal is transmitted via a substrate. In the stingless bee (Melipona), the scout stimulates foragers to fly out for food by emitting special sounds. They are perceived by vibroreceptors, as covering the hive floor with rubber completely eliminates the reaction [163].
The analysis of the functional organization of vibrorecursors indicates that they are adapted to the perception of communication signals. For example, in termites (Zootermopsis angusticollis), the optimal frequency of the subgenual sensilla (1.15 kHz) almost coincides with the dominant frequency of the alarm signal (1.14 kHz). A similar correspondence exists between the frequency optimum of ant receptors (Atta) and the spectrum of "distress signals" passed through the soil.
In addition to vibrations of the solid substrate, insects can perceive vibrations of the surface film of water. Waterflies (Gerridae) use such waves not only to detect prey (insects floating on the surface) but also for intraspecific communication during the breeding season. The perception of vibrations is carried out by various mechanoreceptors in the legs. Their minimum response thresholds reach 1 µm at a frequency of 200-300 Hz.
The Joistone organ performs these functions in the Verticillium beetles (Gyrinidae). The second segment of their antennae glides through the water and the thickened flagellum, which is movably articulated with it, is positioned above the surface. Fluctuations of the second segment cause it to move relative to the flagellum, resulting in the excitation of chordotonal sensillae. In general, the antenna is a vibratory system with a resonance frequency close to 250 Hz. In the frequency range below 150Hz it acts as an acceleration meter. According to electrophysiological data, the receptor responds to vibrations whose amplitude reaches several microns, and its sensitivity increases with increasing frequency. During movement, beetles can detect surface film curvature (meniscus) near obstacles from a distance of 0.5-1.5 cm and avoid collisions [165].
The effect of acoustic waves on the body of the plant pest . The acoustic method of the Colorado potato beetle extermination is based on the physical principle consisting in mechanical impact on the tissues of the beetle organs by pressure followed by their rupture. The method differs from those developed earlier by G.I. Sokol [164-167] in that the mechanical action is made by acoustic oscillations with the amplitude of sound pressure in air equal to the ratio of the force of rupture of connective tissues and organs of the beetle to their section area, with frequency equal to natural frequency of the beetle body or natural frequency of one of its vital organs. There is some experimental evidence in the literature that the resonance frequencies of human organs [168]. Lie in the region of frequencies below 60 Hz. The range of resonance frequencies of individual human organs (head 20-100 Hz, vestibular system from 0.5 to 13 Hz, heart from 4 to 6 Hz). The destructive resonance frequencies for plant pests are not given in the literature.
However, there are data on mechanical characteristics of biological tissues (skin, muscles, tissues of internal organs, bones, cartilage, etc.). In the work of T. N. Pashovkin and A. P. Sarvazyan [169-170] it was suggested that high informative value of mechanical characteristics is caused by the presence and quality of contacts between the elements composing a tissue. It was proposed to estimate mechanical characteristics of biological tissues by dynamic shear modulus and dynamic viscosity. Data on visco-elastic properties of soft tissues (kidney, liver, heart, intestines, spleen, skin, brain) of rabbits, frogs, chickens and human skin are given. The mechanical characteristics of the tissue of plant pests were not investigated in this work.
When an insect pest body is placed in an acoustic field (see figure 2.17 for a diagram of the effect of acoustic waves on an insect body), the wave impact is described by the overpressure, i.e. the sound pressure p_i , which is found from the equation for a plane wave
, (2.2)
where p- sound pressure, t-time, s₀ - speed of sound, x-coordinate.
His solution for p_i has the well-known form