Social Insects & Insects Behaviour PDF

Topic 5 [Part B]: SOCIAL INSECTS & INSECTS BEHAVIOUR  Outline Social Insects - Introduction - Degrees of Sociality - Characteristics - Examples: termites, honey bees, ants Insects Behaviour - Tactile - Chemical - Acoustic - Visual  Int...

Topic 5 [Part B]: SOCIAL INSECTS & INSECTS BEHAVIOUR  Outline Social Insects - Introduction - Degrees of Sociality - Characteristics - Examples: termites, honey bees, ants Insects Behaviour - Tactile - Chemical - Acoustic - Visual  Introduction to Insects Behaviour Insects Behavior: an internally directed system of adaptive activities that facilitate survival and reproduction. Ethology: the scientific study of animal behavior -- particularly when that behavior occurs in the context of an animal's natural environment. Insects have always been popular as subjects for behavioral research because, in comparison to vertebrates, they have relatively simple nervous systems, they exhibit discrete responses to external stimuli, and they are more conducive to ethical experimentation.  Why do insects communicate? Recognition of kin or nestmates Locating or identifying a member of the opposite sex Facilitation of courtship and mating Giving directions for location of food or other resources Regulating spatial distribution of individuals -- aggregation or dispersal; establishing and maintaining a territory Warning of danger; setting off an alarm Advertising one's presence or location Expressing threat or submission (agonistic behaviors) Deception / mimicry  How do insects communicate? Insects use their 5 senses to acquire information about their environment Any of these sensory modalities may serve as a pathway for the exchange of information. Taste and touch are both contact senses, therefore, exchange of information can occur only when two individuals are touching one another. Vision, olfaction (smell), and hearing are remote senses -- information signals may propogate through the air (or water) over considerable distances.  Categories of Insects Sensory Receptors Category Function Examples Detect movements, Tactile receptors vibrations, or other Mechanoreceptors Proprioceptors mechanical Sound receptors disturbances Detect the presence of chemical Taste buds on palps Chemoreceptors substances in the air Antennal sensilla (smell) or on substrates (taste) Detect the presence and quality of incident Compound eyes Photoreceptors light (electromagnetic Ocelli radiation)  Mechanoreceptors Tactile communication Antennal tapping is an essential component of communication in both ants and termites. Antennal tapping on the hind legs is used during tandem running in both ants and termites. This is a "follow-the- leader" behavior in which the tapping informs the leader that she has not lost her disciple. It's not clear exactly what information may be exchanged, but it certainly involves nestmate recognition and leads to exchange of food through trophallaxis. The "dance" language of honeybees is largely a tactile communication system, performed in total darkness on the vertical surface of the honeycomb. Certain treehoppers (Hemiptera: Membracidae) produce vibrations in the tissue of their host plant that can be felt by all other treehoppers on the same plant. Mechanoreceptors Acoustic Communication Sound serves as a very effective communication modality. It can be made to vary in frequency (high pitch vs. low pitch), amplitude (loudness), and periodicity (the temporal pattern of freqency and amplitude). Some grasshoppers and moths, for example, produce ultrasonic sounds as high as 80,000 hertz. Most insects detect sound with a tympanic membrane in the abdomen (e.g. grasshoppers and moths) or in the tibiae of the front legs (e.g. crickets and katydids). Mosquitoes have antennal hairs that resonate to certain frequencies of sound. Sound vibrations can also travel through solid objects, and some insects (e.g. some species of ants, bees, termites, and treehoppers) can sense substrate vibrations with mechanoreceptor (chordotonal organs) in their legs. Since these signals are "felt" rather than "heard", they are usually regarded as a form of tactile communication. Advantages of acoustic communication: Not limited by environmental barriers Effective over distances and around corners Highly variable, fast change -- high information content Disadvantages of acoustic communication : May reveal location of sender to a potential predator Less effective in "noisy" environments (e.g. seashore) May be metabolically "expensive" to produce Attenuation -- intensity falls rapidly with distance from source (cube-root function) Special mechanisms – Frictional mechanisms Stridulation in crickets & katydids. Crickets & katydids rub their forewings (tegmina) together. One wing has a ‘scraper’ while the other has a ‘file’. Stridulation is mostly for attracting a mate, or as a form of territorial behaviour, but can also be a warning signal. Special mechanisms – Vibrating mechanisms Cicadas have a ‘tymbal’ – an elastic membrane stretched over a hollow cavity in the 1st and 2nd abdominal segments. Rapid muscle contractions cause high frequency vibrations that are amplified by the hollow area. The tone can be regulated by the tension across the membrane. Mechanoreceptors The Dancing Bees http://www.polarization.com/bees/bees.html Karl von Frisch, 1886-1982 ◼ Austrian, began work in 1919 ◼ Trained European honey bees, Apis mellifera, to feeders ◼ First believed bees used flower scents or other odors to find food sources ◼ Began to pay close attention to dances performed by returning foragers This slide will be further ◼ Dances very precise, with discussed during our varying tempo and direction synchronize lecture (Webex meeting)  von Frisch described the dances 1. “Round dance” When food source is < 50 m from hive 2. “Waggle dance” When food source is > 50 meters away Waggle run - Abdomen wagging and wing fluttering -Angle repeated with respect to vertical, or gravity (here 20° right)  The bee runs up on the vertical She runs down to tell them to fly comb on the wagging part of the away from the sun. The number of dance to tell other workers to fly runs in a given time indicates the toward the sun. distance. The larger waggle peak – the more distant of the food source. The angle at which she runs on the The drawings do not show that the wagging part of the dance gives the scout is surrounded by workers who angle of the food source relative to follow her movements with their the hive and the sun. antennae. The bee will moves vertically upwards & the angle repeated with respect to vertical, or gravity (here 60° right or 120° right), which means the direction of food source is 60° or 120° right towards the sun. Chemoreceptors Chemical communication Insects probably rely more heavily on chemical signals than on any other form of communication. These signals, often called semiochemicals or infochemicals, serve as a form of "language" that helps to mediate interactions between organisms. Insects may be highly sensitive to low concentrations of these chemicals -- in some cases, a few molecules may be enough to elicit a response. Advantages of chemical communication: Not limited by environmental barriers Effective over distances and around corners Effective either day or night Longer lasting than visual or auditory signals Metabolically "inexpensive" because only small quantities are needed Disadvantages of chemical communication: Low information content (presence/absence) Not effective in an upwind direction Can be divided into 2 groups based on who "sends" a message and who "receives" it: - Pheromones are chemical signals that carry information from one individual to another member of the same species. These include sex attractants, trail marking compounds, alarm substances, and many other intraspecific messages. - Allelochemicals are signals that travel from one animal to some member of a different species. These include defensive signals such as repellents, compounds used to locate suitable host plants, and a vast array of other substances that regulate interspecific behaviors. There are two types of pheromones: releasers primers. Releasers cause an immediate behavioral response in the receiving individual, whereas primers cause longterm physiological changes in receivers. Releasers: a) Sex attractants: often released by female, attracts males from long distances (> 1 km) b) Aggregation: brings many conspecifics together quickly (e.g. mass attack of bark beetles on trees to overcome resin defenses) c) Spacing (epideictic): evoke behaviors that lead to increased space between individuals (e.g. apple maggot fly’s oviposition deterrent pheromone) d) Alarm: stimulates escape or other defensive behaviors (e.g. aphid attacked by predator causes conspecifics to disperse; honeybee sting incites nestmates to sting, hissing in cockroach) e) Trail: insects lay a trail to food sources (e.g. foraging ants) Primers Colony pheromones: social insects – kin and colony recognition; control of reproduction and kin number, foraging behavior. ‘The glue that holds the colony together.’ Note that these pheromones, normally produced by the queen, have both releaser and primer effects. Produced by mandibular glands.  Photoreceptors Visual communication Many insects communicate with visual signals. Some insects use bright colors, eyespots, or other distinctive patterns to scare away predators, to advertise their ability to sting, or to mimic the appearance of another unpalatable species. Other insects use dance-like body movements to attract a mate or to communicate with nestmates. Most of these signals are effective only as long as they are visible in daylight. But a few insects (fireflies, for example) can generate their own light and use visual signals that can be seen at night.  Passive signals, such as eyespots and color patterns can serve as a form of "free advertising". Active signals, like body movements and light flashes, are more costly to produce, but they can be withheld from use at inappropriate times. In fireflies, for example, pulses of light are used in a courtship dialogue between a male (usually flying) and a female (usually perched in the vegetation). Other examples: - Bioluminescence occurs in some collembolans, cicadas, fungus, gnats and beetles - Bolitophila luminosus, the New Zealand glow worm (Diptera) - larvae produce light by modified Malpighian tubules. These cave dwellers catch small flying insects attracted to the light on sticky threads  Best studied are the fireflies (Coleoptera: Lampyridae, e.g. Photinus spp.) Have a flashing organ in the abdomen (both sexes or females only depending on the species), used in mating The pattern of flashes (duration and frequency) is species-specific The predatory lampyrid Photurus mimics the flash pattern of female Photinus, luring male Photinus that it then eats…  Photoreceptors Insect color vision Unlike humans, many insects have the ability to see ultraviolet light. Some species communicate using wavelengths in this part of the spectrum. This slide will be further discussed Female cabbage butterflies, for example, have during our ultraviolet-reflecting scales on the dorsal wing synchronize lecture surface. (Webex meeting) When they fly, each downstroke of the wing creates a brief "flash" of UV that males apparently recognize as the flight signature of a potential mate. A "flashing female" may attract several males who engage in aerial courtship displays.  Like most animals, insects use their sight to help them make sense of their surroundings. But their large compound eyes work in a different way from human eyes. Rather than having a single lens in each eye, an insect may have hundreds or thousands of “mini eyes” that create a mosaic-type image. Many insects with compound eyes have color vision, but very few—aside from butterflies—can see red. They are better at seeing shades of blue. Butterflies can also detect ultraviolet light, which is invisible to the human eye. This allows them to see special patterns on the petals of flowers, which guide them to the nectar they feed on. Most insects have only two types of visual pigments. One pigment absorbs green and yellow light (550 nm); the other absorbs blue and ultraviolet light (