Chapter 3 Communication and Sociality 36 3. Communication and Sociality Receptors and senses have been outlined in This chapter also looks at insect societies, chapter 2.2.6. Their outstanding performance following the evolution from simple aggrega- is one of the keys to the success of insects. tions to social insects culminating in the Receptors are essential devices of a receiver eusocial termites and Hymenoptera like bees, and can be compared with a satellite dish or some wasps and all ants. antenna. A TV set doesn’t work without these devices, similarly an insect requires receptors to respond. Communication and behaviour 3.1 Communication depend on information acquired by receptors. One might tend to believe that insects do not The simplest type of behaviour might be a have much to say, as stated by Piau, J. and reflex. This is a simple reaction as a result of Lynch, J. in “Communication and Language - a particular stimulus, for instance the sponta- Reader” (UPNG; Waigani; PNG; 1989): neous withdrawal of the hand from a source of “Insects have a very limited number of messages that heat. There are two types of movements they can say or receive. The male of a certain species of triggered by a simple stimulus. An unoriented grasshopper, for example, has a choice of six messages, action varying with the intensity of the which might be translated as follows: stimulus is called kinesis. We talk about · I am happy, life is good taxis, if the movement is towards (positive · I would like to make love · You are trespassing on my territory taxis) or away from the stimulus (negative · She’s mine taxis). According to the quality of the stimulus · Let’s make love chemo- (related to taste and scent), geo- (re- · Oh how nice to have made love” lated to gravity), hygro- (related to humidity), Communication between insects is mainly photo- (related to light), thermo- (related to about reproduction, food and territory and temperature), phono- (related to sound) -taxis definitely not about rugby and politics. Since or -kinesis can be defined. Using these terms, we are far away from having a holistic a positive phototaxis is a movement towards conception of the complex communication light, for instance a plant growing towards processes, especially of social insects, we do light or a nocturnal insect, like a moth, being not exactly know whether or not there are attracted to a light source (see also chapter more messages that insects exchange. 7.5). When an insect follows a gradient, for Communication is defined as information instance the concentration of a pheromone as being sent by one individual (sender) and shown in fig. 3-5, it is called klinotaxis. perceived by one or several other individuals Insect behaviour generally is innate and (receiver): determined genetically, but simple learning has been observed in some bees and butter- sender receiver flies. information The information can be transmitted either Different types of communication are dis- between individuals of the same species cussed in this chapter. Communication enables cooperation, without communication (intraspecific) or between individuals of no cooperation. One can easily figure out the different species (interspecific). The medium chaos as a result of a lack of communication for signal transduction in insects is either of and cooperation for example in a termite auditory, visual, tactile or chemical nature. colony of several million individuals, equi- valent to the population of PNG. Complex 3.1.1 Auditory Communication behaviour based on communication includes territorial behaviour, courtship, brood care In tropical countries sound-producing insects and parental care. The latter is important for can be recognised almost all day and night. the understanding of how sociality in insects Amongst those producing sound, cicadas, evolved. crickets and grasshoppers are definitely the 3. Communication and Sociality 37 most conspicuous ones. Cicadas are the There are several ways of producing sounds: animals producing the loudest sounds in terms Air forced through or over small openings of sound pressure, although a barking or causes a hissing sound. This can be experi- howling dog might seem louder to us humans. enced, when the Rhinoceros beetle Xylotrupes This is because the main frequency range of a gideon is touched. cicada is above 20,000 Hz, beyond the detectable frequency range of human beings. Stridulation or frictional rubbing is the result Sonograms display the frequency of sound of two parts of the body being scraped waves as a function of time. The sonograms together. The chirp of a grasshopper or cricket of some insect sounds are shown in fig. 3-1. is produced by scraping the front part of the hind wing over the thickened veins of the forewings. Other grasshoppers possess file- like structures on the forewings as shown in fig. 3-2, that are rubbed over the inner side of the hind femur. Particular assassin bugs (Reduviidae) rub the tip of their proboscis A along a file on the ventral part of their abdomen (see fig. 3-3). B C D Fig. 3-2: Stridulatory file under tegmen of a Tettigoniidae grasshopper which is rubbed over the hind femur (reproduced from CSIRO, 1991) E F Fig. 3-1: Sonograms of insect sounds: (A) Assassin bug Canthesancus sp., (B) Drummer cicada Thopa sp., (C) Black Field cricket Teleogryllus sp., (D) Bush cricket Tettigonia Fig. 3-3: Stridulatory file on ventral part of sp., (E) Mole cricket Gryllotalpa sp., (F) thorax of a Reduviidae bug. The tip of the Death’s Head moth Acherontia sp. (reproduced proboscis is scraped along the file to produce by permission of CSIRO Australia from CSIRO, 1996²) sound (reproduced from CSIRO, 1991) 38 3. Communication and Sociality A vibrating membrane called a musical The production of sounds serves various apparatus is used by cicadas for the purposes. Some insects mark their territory by production of sound. One out of a set of means of sound and for many, sound is the several membranes in ventral pouches at the medium of communication for courtship and base of the abdomen (see fig. 3-4) is reproduction. The hissing sound of a Rhinoc- connected with a muscle, that pulls the eros beetle upon disturbance is definitely a membrane inwards. Upon relaxation of the defence strategy. Other examples for audible muscle, the membrane snaps back, causing defence are particular Tiger moths (Arcti- vibrations that are amplified by other idae). These animals are able to produce and membranes. This process is repeated several detect ultra sound. Bats use ultrasound for thousand times per second. their echolocation system in order to detect obstacles and prey during the night. Tiger moths thus are able to recognise an approaching bat. A number of disastrous Tiger moths use ultrasound to tell the bat: “I am distasteful, unpalatable to you, leave me in peace”. Other Tiger moths make a lot of ultrasonic noise and in this way disturb the bat’s echolocation system. As a result of this interference, the bat loses orientation and cannot get the moths. 3.1.2 Visual Communication Visual communication seems to be well developed in insects for various purposes. Bright coloration (warning or aposematic coloration) of wings and other body parts, as is the case in many moths and butterflies (Lepidoptera) and in bees and wasps (Hymenoptera), plays an important role for defence as visual mimicry (see chapter 4.4.5). Colours also stimulate sexual behav- iour. Some insects have the ability to display glowing light in darkness, a phenomenon, called bioluminescence. This is an energy requiring reaction triggered by the enzyme luciferase. Common examples are beetles like fireflies and their larvae, the glow-worms (Lampyridae), click beetles (Elateridae), Fig. 3-4: Musical apparatus of a cicada some springtails (Collembola), the lantern (Cicadidae). Tymbal cover and operculum bug (Fulgoroidae) and a few species of true removed at bottom (reproduced from CSIRO, 1991) flies (Diptera). Bioluminescence is used for courtship signalling and prey-luring. Beating substrate with parts of the insect body is done for instance by some termite 3.1.3 Chemical Communication soldiers hitting wood with the tips of their mandibles or by some grasshoppers using The most important means of communication their hind tibiae as drum sticks, hitting the in insects is the use of chemical signals ground. involving the senses of smell and taste. No 3. Communication and Sociality 39 other group of animals has developed such a Allelochemicals facilitate communication variety of hundreds of chemical substances for between individuals of different species. the communication between all stages of the These substances can be further grouped into life cycle and sexes. These communication kairomones, allomones and synomones. chemicals or semiochemicals are produced by Kairomones benefit the receiver but dis- exocrine glands and released into the envi- advantage the producer. An example is the ronment. Generally they can be classified as host-plant detection by a phytophagous insect. pheromones and allelochemicals. Termites or bark beetles are attracted to the The volatile pheromones are used for scent released by a damaged, thus weakened communication within individuals of the same host-tree. Allomones benefit the producer, but species as trace indicators for instance by have no effect on the receiver as is the case ants, as courtship pheromones and sex with defensive chemicals. Synomones are attractants eg. by moths, as aggregation advantageous for the producer and the pheromones, spacing pheromones, alarm receiver. Using the damaged host-tree of the indicators and for the control of castes in above example, a parasitoid of the bark beetle social insects. The location of a female, benefits from the allelochemical. The paras- emitting a sex attractant is shown in fig. 3-5. itoid is attracted to the damaged tree and finds Sex attractants can be used for the biological its host, the bark beetles.