Insects generally communicate to locate their food source and mate, using
- Light Production
- Sound Production
“substances that are secreted to the outside by an individual and received by a second individual of the same species in which they release a specific reaction”.Pheromones are mostly volatile but sometimes they are liquid. All pheromones are produced by exocrine glands, derived from epidermal cells. The scent organs may be located anywhere on the body.(eg)
(i) Female lepidoptera – eversible sacs or pouches between the 8th and 9th abdominal segment.
(ii) Female honey bee – mandibular glands
(iii) Female aphids – hind tibia
(iv) Female cockroach – midgut Further classification of pheromones is based on categories of behaviour associated with sex, aggregation, spacing, trial forming and alarms.
(i) Sex Phermones : Used for mate location and courtship (eg) Queen butterfly Danaus gilippus : Male insect produces courtship pheromone an alkaloid called danaidone.
(ii) Aggregation pheromones: Causes insects of both sexes to crowd around the source of the pheromone. This may lead to increased chances of mating. The other benefits being, security from predation, maximum utilization of scarce food resource, overcoming of host resistance and cohesion of social insects. e.g. Cockroaches and scolytid beetles.
(iii) Spacing phermones: Produces appropriate spacing on food resources. (eg) Many Tephritid flies lay eggs singly in fruit where a single maggot is to develop. Here the female deposits an oviposition deterrent pheromone on the fruit to avoid subsequent oviposition.
(iv) Trial – marking pheromones : Many social insects use this pheromone to mark their trails to food and the nest. This pheromone is volatile and short-lived. (eg) In ants the trial pheromone are commonly metabolic waste products excreted by the poison gland. These need not be species specific – several species share some common chemicals.
(v) Alarm pheromones : This causes alarm behaviour. Alarm is provoked by the presence of predator or in many social insects by the threat to the nest.
II. Light production:
The principal role of light emission is in courtship signalling and prey finding. This involves species specific variation in duration, number and rate of flashes in a pattern and the frequency of repetition of the pattern.
(eg) Lampyrid beetle (fire fly) Luciferin Luciferase
Variation in ATP release controls the rate of flashing and differences in pH, controls frequency and colour of light emitted.
III. Sound Production:
It is useful in location of mate. (eg) Mosquitoes, Cicada.