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Authour: Khalil Shaikh

CoFounder, Sales Director & Technology Head @ Microbiz Network India

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Insect Communication System


Insects

Insects are the most successful group of living things in terms of the number of species, the biomass and their extreme survival and reproduction capabilities. Entomological research has revealed that insect sensory systems are crucial for their extremely successful conquering and exploitation of every habitat niche on earth planet. Compared with human beings, insect central nerve system (mainly brain) is extremely primitive, simple both structurally and functionally, and is of minimal learning ability.  Faced with these constraints, insects have evolved a set of extremely effective sensory systems with features such as structurally simple (e.g., some sensor receptors are single cells), functionally versatile and powerful, highly distributed, as well as noise and fault tolerant, etc.  As a result, in recent years, significant advances in this interdisciplinary field have been achieved.  However, we believe that the potential of this field is far from being fully recognized. In particular, the contrasting similarity between the ubiquitous existences of insect sensory networks in nature and the ideal of pervasive computing has received little attention. This article attempts to introduce engineers and computer scientists to a comprehensive view of insect sensor systems, identifying areas that have a high potential for new directions.  It attempts to point the reader directly to the state-of-the-art advances, narrowly guiding though an enormous body of research from the field of insect sensory systems.  We hope that this article will lead to new inspirations and research directions in communication and computing systems.  

The extant number of species of insects on earth is estimated between 2-10 million, and of the about one million scientifically identified animals, 72% are insects (Peters 1988).  Insect species outnumber all other organisms combined.  So why are there so many insects and why are they so successful in conquering the planet? There are a variety of factors and the following four are among the most frequently cited: (1) the high level of organization of insect sensory and neuromotor systems, (2) the minimal learning capacity and short generation time, (3) the small size, and (4) the nature of the co-evolutionary interactions that involve insects

Insect Sensory ecology

 Insect sensory ecology is a very recent term, although the problem domain it addresses has been studied for a long time.  It is defined as the study of how insects use a sensory information in their interactions with the environment.  Sensory ecology is broader than already established chemical ecology since it also implicates physics, chemistry, physiology behind the generation and perception of stimuli.  Its focus is on the adaptive use of sensory stimuli. It is generally recognized that insects’ adaptations are imperfect compromises between conflicting selective pressures working within the physical constraints and the evolutionary history of an insect species. 

Signal detection

 Insects depend on sensory receptors to detect stimuli.  It has been established that insect sensory receptors often operate at their maximum theoretical sensitivity, e.g. the detections of single photons or odour molecules have been documented.  However, the absolute sensitivity, although certainly appealing for engineering design to improve sensor sensitivity, is often not the dominant adaptive factor.  It turns out that insects have evolved very diverse adaptive strategies to improve signal/noise ratios in their sensory systems.  One common strategy to filter out noise in low-intensity signals is to use the so-called summation, i.e., averaging many neurons over extended time periods to obtain a more reliable estimation.  The summation over space is demonstrated by some male moths with enlarged antenna covered with tens of thousands of receptor tuned to detect specific components in female-released sex pheromone blends and other signals.  Another interesting strategy to improve signal/noise ratio is to detect and amplify primarily those features of the signals that are of particular interests, they are termed as “feature detectors” or “matched filters” in the insect sensory research literature. 

 Although the number of insect species exceeds the total species number of all other living things combined, they exhibit remarkable niche specialization.  For example, the vast majority of insects feed on single or a few related host species.  One of the explanations for the high specialization is a sensory limitation.  The justification for the hypothesis is that selecting a combination of a few predictable stimuli that indicate essential resources (such as hosts) with high certainty, promotes the sensory systems to maximize the efficiency of resource utilization.  The signal specialization may also be helpful for avoiding catastrophic mistakes.

Sensory system model 

To describe the sensory signals communications of insects the conceptual emitter-medium-receiver model is proposed and developed their researchers at Microbiz.  The emitters may be animate or inanimate objects, but usually, they refer to the form, er, e.g. other insects.  Whereas this model was developed in the context of sensory signals communication, the principle seems to hold in communication systems using other types of signals.

Most of the signals in insect communication are sensory signals and the communication medium is generally the “air airwaveut also can be water or other substrates.  This communication model is very similar to wireless communication in engineering.  The model is an extremely simplified view and the intricacies in the insect chemosensory system often surprise researchers.  For example, in the 1970s scientists already discovered that there are some insects (such as the clearwing moth in the family of Sesiidae) where the male and female communicate by identifying the blend ratios of isomers of sex-pheromone compounds released by females. This means, different species encode their communication channels by manipulating the ratios of isomer blends, although the same pheromone compounds may also be used by their relative species.  This mechanism is used in “long range” communications between male and female clearwing moths before they enter the same courtship area.  Reproductive isolation is essential for biological species (interspecies mating is harmful and “prohibited” in higher animals and species).  The fact that clearwing moths depend on encoding the isomer blends of sex-pheromones to ensure that only males of the same species can decode the signals transmitted by the female-released pheromone is a proof for the reliability of the system.  However, the communication is sufficiently reliable, but not perfect.  

In the emitter-receiver model , two forms of exploitations may occur.  First, the emitter may be exploited by enemies that are able to decode and locate the signals, e.g. parasitoids and predator.  Second, predators acting as impersonators using similar signals may lure the receiver.  These exploitations have motivated extensive studies in entomology and pest management on insect sensory signals, since they provide insect pest control measures safe to the environment and human health.  In the context of wireless sensor networks, the inspiration may come from the imperfect communication mechanisms that still guarantee the survival of the species (from extinction) in its evolutionary history.  

The evolutionary process to adapt to the two aforementioned exploitations is very interesting.  Scientists believe that if the interactions are beneficial to emitter and receiver, true communication often evolves.  Specifically, the sender and receiver can agree on a signal and its meaning and evolve to optimize the signal transmission and processing, while excluding unwanted impersonators. When the interaction is detrimental, the emitter may opt out by so-called crypsis mechanisms with which it reduces or confounds the signal.  As a result, the receiver increases its signal processing capacity to better distinguish undesirable signals from adaptive ones. 

Sensory System Cost and Constraints

The cost associated with the development of sensory signalling system of insects is extremely higher, looking at the high ratio of sensory organs to body mass or size.  For  development of vision communication , the complex electrical coding of the compound eyes  insects and measuring behavioural response to visionary signals is massive task consumes lot of man-hour time and financial resources.  

There is little research on how insects optimize the interpret the sensory signals .  However, it can be expected that they must have evolved intricate strategies and tactics, given the extremely high stake in the overall energy allocation and the crucial importance of their sensory systems.  Knowledge of how insects optimally allocate energy to their sensory system may provide useful insights for designing energy efficient sensor networks.