Communication between Insects By April Abstract

Transcription

1 Communication between Insects By April 2011 Abstract Communication between insects is one of the most important keys in insect life and survival. Insects are able to communicate in many different ways, including sound, chemicals, dances or visual cues, and vibrations. Male crickets use their wings to sing to females as a means of mate attraction. These songs are species specific and can also help with mate location. Apismellifera, otherwise known as the honeybee, shows a peculiar waggle dance to show its fellow foragers in the hive the location of nearby and even distant food sources. Outdoor experiments using bee tagging and observations of the tagged bees at the food source and the nest have given evidence for this. In Drosophila melanogaster it has been found that chemical signals such as the cuticular hydrocarbons are used in both sexual and species identification. Different experiments have been run with the females and males of this species, taking away and adding different pheromones to see which pheromones were involved in species and sexual identification. Nezaraviridula, otherwise known as the stink bug, uses vibrations as sound to communicate with one another. This species can use species and sex specific vibrations as signals to other members of the species, not only giving information into sex and species but also location for potential mates. There are many more examples of communication in insects. These four mechanisms mentioned above and the species that use them are very good examples in showing how insects can communicate in order to survive. 1

2 Introduction Insects are fascinating creatures when it comes to the different ways they can communicate with each other. Not unlike humans, insects will use these different methods of communication in order to live as a society or species, and to maintain the survival of their species. One of the more popular mechanisms of insect communication is the use of sound or noise to speak with each other. Crickets, grasshoppers, katydids, and cicadas all use air-borne sounds as a means of communication. 1 Due to their larger size, this form of communication is more effective than for smaller insects because the sound source should be about ¼ the size of the sound wavelength for optimal power and range. 2 These acoustically communicating insects have ears just like people. Unlike people who have only two, however, insects contain at least one ear on almost every part of their body. 3 Insects can use their ears to either escape predators or listen to each other through auditory cues as a means of communication. While predation is thought to be the selection pressure for high sensitivity and short latency, communication is thought to be the selection pressure for sound localization and song recognition which is essential for mate recognition. 3 Insects use song recognition in order to identify its own species as well as sex. The two aspects of song recognition are the spectral composition or the amplitude modulation of the signal which are both used in the recognition of the species. 3 Insects use song localization to find the direction of the insect s species song. Another popular mechanism of insect communication is the use of chemicals. 2

3 Insects use certain types of chemicals known as releaser pheromones for communicating certain things that initiate behavioral responses immediately. 4 The three types of releaser pheromones include sex, alarm, and recruitment. 4 The sex pheromones are very sensitive and species-specific and are responsible for all of the sexual behaviors of the insect. 4 Knowing when an insect has come into contact with another insect of the opposite sex and the same species is critical in survival of the species as a whole. The colony alarm system of social insects helps alarm the colony of attacks. The alarm system is the alarm pheromone which is less sensitive than its sex pheromone counterpart, though the shear amount that is released is the deciding factor of whether the alarm will be raised. 4 And finally, the recruiting of fellow insects to different food sources or paths is made possible by the recruiting pheromone. 4 Ants use this type of pheromone to mark the paths to food sources while bees leave the pheromone only at the food source. 4 Some of the best examples of this type of communication occur in bees, ants, and the fruit fly Drosophila melongaster. Like humans, insects don t need to speak with each other in order to communicate, but can simply use different behavioral actions to communicate. Imagine being able to dance for a friend and portray the direction and distance that a McDonalds or Wendy s is from your current location by the shear length of the dance. The honeybee Apismellifera can accomplish this by using different types of dances known as waggle or round dances in order to communicate direction and distance of different food sources. 5 Three male species of grasshoppers are known to use anywhere from pronotal bobbing to lateral swinging or frontal swinging as courtship methods for female 3

4 grasshoppers. 6 Some of these courtships have even been found to be so similar that heterospecific mating can occur between grasshoppers of different species. 6 Finally, smaller insects have developed a way to communicate which is more efficient for their size and can reach far distances with respect to their small size. 1 The mechanism for this type of communication involves vibrations through substrates in the air, water, or the surface upon which an insect perches. 1 Insects contain receptors in their six legs that detect these vibrations. Signals are sent to the brain relaying the signal trying to be portrayed by the vibrations of the communicating insect. 1 A prime example of this type of communication that has had many studies performed on it is the stink bug Nezaraviridula. Communication with Sound One of the best examples of acoustically communicating insects is the cricket. The most studied cricket is the field cricket of the Gryllusspecies. 7 Crickets, as opposed to other insects, birds, frogs, and other acoustically communicating mammals who use many frequency components, use almost pure tones. 7 Males use these pure tones for a species-specific way to attract females. Field cricket males build burrows and sit close by singing the song of their species ready to dash back into their holes in case a predator hears the song and decides to investigate. 7 If a female cricket is nearby and hears the call she will first use song recognition to identify if the song is being sang by a male cricket of her species. After identifying the male caller as being of her species the female cricket will start using sound localization to figure out what direction the call is coming from, and she will slowly make her way towards it. Observations have seen females walking 4

5 toward singing males as far as several meters away which is pretty remarkable for the excess attenuation and the small size of the insect. 7 Once a female cricket has found the source of the song, her male caller will change his tune to that of a courting song. 7 The mechanism by which crickets create their song is very interesting. Crickets like many other insects possess a pair of wings which they use as their musical instruments. Field crickets, which produce their call at about 4.5kHz, use two mechanisms of frequency multiplication and sound emission to produce their song. 7 Frequency multiplication involves slow muscular contractions that cause a scraper on one wing to rub the cuticular teeth on the other wing. 7 The resulting wing vibration creates the harmonics of the call based on the rate at which the scraper hits each tooth per unit of time. 7 Sound emission involves a large triangular surface on the wings of the cricket known as the harp. 7 The harp acts as a resonator and is essentially responsible for the frequency of the crickets song. 7 Though sound communication is obviously an effective form of communication, what if you don t want anybody listening to what you have to say? Much like a human whisper, Ostriniafurnacalis or the Asian corn borer moth has developed a type of quiet acoustical sexual communication. 8 While the loud calls of the cricket or cicadas have been found to be effective in mating success, this method can also be costly. You never know if a competitor, predator, or parasitoid might be listening. 8 O. furnacalisuses low-intensity ultrasonic songs in its sexual communication. Many moth species possess ultrasoundsensitive tympanal ears which they use in this type of communication. The O. furnacalisalso possesses specialized scales on it forewings and thorax which have been 5

6 found to be the instrument this moth uses in its songs. 8 The rubbing of these scales together produces ultrasonic songs at 46dB sound level at 1 centimeter. 8 Female moths of this species have an escape behavior that is suppressed by this low-intensity ultrasonic song. 8 Mating success is then greatly increased because the females of the species are not trying to escape as much, allowing for longer copulation time for the males. Communication with Chemicals Pheromones make up the chemicals that insects use to communicate with each other. These pheromones are like signals that trigger certain physiological responses of the insect based on the type of pheromone. Though olfactory and gustatory receptors in the antennae, maxillary palps, labellum, and forelegs are thought to be responsible for pheromone detection no specific ligands have been recognized for pheromone receptors. 9 Hydrocarbons are the pheromones used by Drosophila melanogaster or by fruit fliesin both sexual and species identification as well as courtship and actual mating behaviors of this species. 9 The alkenes inside the hydrocarbon chains have been identified to be the main keys in sexual and species determination. 9 The males and females of this species release different pheromone types. In fact if you give a female the male pheromones other males will become aggressive toward that female even if the male has just previously copulated with the female. 10 Some of the female hormones act as aphrodisiacs and can in fact cause males to be tricked into trying to copulate with other males as well. 9 Even different male fly species could be tricked into mating with the females of the D. melanogaster species. 9 This shows how much pheromones can influence a fruit fly s 6

7 behavior, and how much this fly must rely on pheromones in order to pick the right mate. Unlike D. melongasterthe stingless bees Trigona corvine use pheromones in the detection of food trails. Foraging workers of this species have been found to release pheromones between a food source and their nest in order to recruit large amounts of workers into foragers themselves. 11 The pheromones can not only give direction and distance but also altitude of the food source with respect to the nest. 11 Recent experiments have shown that the T. corvine release this recruiting pheromone by the labial glands while alarm pheromones have been found to be released the mandibular glands. 11 Receptors in the antenna are used by the T. corvine workers in order to receive the signals from these pheromones. 11 Another interesting thing about the recruiting pheromones in T. corvine is the fact that they are nest specific. 11 This is very critical for the survival of colonies because you don t want your workers getting on the trails of different colony stingless bees than your own even if they are the same species. This way each colony keeps its colony members and can maintain a population that is suitable for the given resources of the colony. Ropalidiasocial wasps are also insects that have taken advantage of the use of pheromones as a means of survival. When predators come calling these wasps need to be on their best organization in order to survive attacks on the nest. Like the T. corvine these wasps have developed defense pheromones to deal with these attacks called alarm pheromones. Most of the species of social wasps studied have been found to release the alarm pheromones from their venom glands. 12 R. flavopictais one of the species of insects that demonstrates this. 12 In small disturbances of R. flavopictanests small amounts of 7

8 alarm pheromone are released causing a few of the wasps to fly out of the nests and land on the nest envelope. 12 Larger disturbances in the nests cause larger amounts of alarm pheromones which require greater action from the colony and could cause the entire colony to fly out of the nest and onto the nest envelope ready for battle. 12 If the disturbance is continued the wasps start flying and swarming toward the disturbance with wings up and intents to sting. 12 Communication with Visual Cues One of the most interesting forms of visual communication in insects is that of the honey bee ApisMellifera. When food distances are more than 100 meters away bees can t simply use pheromones or acoustical songs because of the shear distance of the food source so this interesting creature has developed a series of dances that it can accurately convey distance and location of long distance food sources. 10 When the food is over 100 meters away the returning forager puts on a show which involves a series of waggle dances. 10 The length of these dances is related to the vector distance of the food from the hive while the orientation of the dance with regard to the sun projects direction of the food source. 10 When the food is less than 100 meters away from the hive the dance turns into more of a round dance. This round dance does not give distance information, but does provide the spectating worker bees a direction for the food source and a knowledge that it is close. 10 Bees are faced with the same language barriers we humans are. Just like we have English, Spanish, and many more languages, bees can have different dialects of their dances between colonies and species. 5 When colonies of Apismelliferaligusicaand 8

9 Apismelliferacarnicaare mixed consistent misunderstandings of food distance from the hive are made in the waggle dances. 5 However, interestingly enough when two different species of honey bees were mixed Apismelliferaligusticaand Apisceranaceranathese bees were able to accurately translate the different waggle dances of each other s species with the same accuracy of their own species dance. 5 Another interesting example of visual communication in insects is that of the grasshopper. Although acoustic calling in grasshoppers is a well known source of communication, grasshoppers visually communicate as a means of courtship and mating. 6 The courtships of the species Tetrixceperoiinclude a sort of pronotal bobbing which involves fast movements of high amplitude while the courtships of T. subulataand T. undulataperform later swinging and frontal swinging. 6 Communication with Vibrations When insects are smaller the loud acoustical calls are not efficient for communication so vibrational communication has developed. The insect Nezaraviridulais a good example of this type of communication in its courting behaviors. The males and females of this species both can produce species and sex specific vibrations. 1 These vibrations have frequency of Hz, and are sang back and forth between the male and female. 1 The vibrations are produced by the movement of the abdominal tegral plate and dorso-ventral vibrations of the abdomen. 1 The stink bugs, as N. viridualis commonly known, have scolopidial organs in each leg, campaniformsensilla, and Johnston s organ in the antenna which are effective in picking up the vibrations. 1 The plants that these stink bugs perch on are also very helpful in propagating the vibration calls this insect. 1 9

10 Hissing and piping of the honey beeapisflorea has been described as the way this type of honey bee raises the alarm and coordinates the defense of the hive. 13 When a bee hive of this species is under attack individuals of the colony start making a piping noise followed less than a second later by the rest of the colony making a synchronized hissing sound much like what a cat would use against a dog. 13 The piping of the individual bees is almost like a conductors leading a symphony of hissing. This piping is performed by individual workers pressing there thorax against the honey comb while producing vibrations through the thorax. 13 While piping and hissing are going on all other activities of the workers and foragers ceases until colony safety is ensured. 13 A similar type of vibrational alarm has been observed in the African fungus growing termite Macrotermes. 14 These vibrational alarms tell the termites to stay inside their colonies until the danger has passed

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