Insect migration is the seasonal movement of insects, particularly those by species of dragonflies, beetles, butterflies and moths. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Anisoptera redirects here For the genus of trees see Anisoptera (tree. Beetles are the group of Insects with the largest number of known Species. A butterfly is an Insect of the order Lepidoptera. Like all Lepidoptera butterflies are notable for their unusual life cycle with a A moth is an Insect closely related to the Butterfly, both being of the order Lepidoptera. The distance can vary from species to species, but in most cases these movements involve large numbers of individuals. In some cases the individuals that migrate in one direction may not return and the next generation may instead migrate in the opposite direction. This is a significant difference from bird migration. Bird migration refers to the regular seasonal journeys undertaken by many species of Birds Bird movements include those made in response to changes in food availability The most famous insect migration is that of the Monarch butterfly which migrates from southern Canada to wintering sites in central Mexico where they spend the winter. The monarch ( Danaus plexippus) is a Milkweed butterfly ( Subfamily Danainae in the family Nymphalidae. In the late winter/early spring, the adult monarchs leave the Transvolcanic mountain range in Mexico for points North. Mating occurs and the females begin seeking out milkweed to lay their eggs, usually first in northern Mexico and southern Texas. The caterpillars hatch and develop into adults that move north, where more offspring can go as far as Central Canada until next migratory cycle.
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Definition
All insects move to some extent. The range of movement can vary from within a few centimeters for some sucking insects and wingless aphids to thousands of kilometres in the case of other insects such as locusts, butterflies and dragonflies. Locust is the Swarming phase of short-horned Grasshoppers of the family Acrididae. A butterfly is an Insect of the order Lepidoptera. Like all Lepidoptera butterflies are notable for their unusual life cycle with a Anisoptera redirects here For the genus of trees see Anisoptera (tree. The definition of migration is therefore particularly difficult in the context of insects. A behaviour oriented definition proposed is
Migratory behaviour is persistent and straightened-out movement effected by the animal's own locomotory exertions or by its active embarkation on a vehicle. It depends upon some temporary inhibition of station-keeping responses but promotes their eventual disinhibition and recurrence.
—Kennedy, 1985[1]
This definition disqualifies movements made in the search of resources and which are terminated upon finding of the resource. Migration on the other hand involves longer distance movement and these movements are not affected by the availability of the resource items.
General patterns
Migrating butterflies fly within a boundary layer, with a specific upper limit above the ground. The air speeds in this region are typically lower than the flight speed of the insect. These 'boundary-layer' migrants include the larger day-flying insects, and their low-altitude flight is obviously easier to observe than that of most high-altitude windborne migrants. [2]
Many migratory species tend to have polymorphic forms, a migratory one and a resident phase. The migratory phases are marked by their well developed and long wings. Such polymorphism is well known in aphids and grasshoppers. In the migratory locusts, there are distinct long and short-winged forms. [3]
Migration being energetically costly has been studied in the context of life-history strategies. It has been suggested that adaptations for migration would be more valuable for insects that live in habitats where resource availability changes seasonally. [4] Others have suggested that species living in isolated islands of suitable habitats are more likely to evolve migratory strategies. The role of migration in gene flow has also been studied in many species. [5]
Orientation
Migration is usually marked by well defined destinations which need navigation and orientation. Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another A flying insect needs to make corrections for crosswinds. [6] It has been demonstrated that many migrating insects sense windspeed and direction and make suitable corrections. [7] Day-flying insects primarily make use of the sun for orientation, however this requires that they compensate for the movement of the sun. Endogenous time-compensation mechanisms have been proposed and tested by releasing migrating butterflies that have been captured and kept in darkness to shift their internal clocks and observing changes in the directions chosen by them. Some species appear to make corrections while it has not been demonstrated in others. [8]
Most insects are capable of sensing polarized light and they are able to use the polarization of the sky when the sun is occluded by clouds. [9] The orientation mechanisms of nocturnal moths and other insects that migrate have not been well studied, however magnetic cues have been suggested in short distance fliers. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. [10]
Recent studies suggest that migratory butterflies may be sensitive to the earth's magnetic field on the basis of the presence of magnetite particles. [11] In an experiment on the monarch butterfly, it was shown that a magnet changed the direction of initial flight of migrating monarch butterflies. [12] However this result was not a strong demonstration since the directions of the experimental butterflies and the controls did not differ significantly in the direction of flight. [13]
Lepidoptera
Migration in the butterflies and moths are particularly well known. The Bogong moth is a native insect of Australia that is known to migrate to cooler climates. The Bogong moth ( Agrotis infusa) is a temperate Species of night-flying Moth notable for appearing in large numbers around major public buildings Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described For a topic outline on this subject see List of basic Australia topics. In southern India, mass migrations of many species are noted prior to the monsoons. A monsoon is a seasonal prevailing wind which lasts for several months [14] As many as 250 species of butterflies in India are migratory. These include members of the Pieridae and Nymphalidae. The Pieridae are a large family of butterflies with about 76 genera containing approximately 1100 species mostly from tropical Africa and Asia The Nymphalidae is a family of about 5000 Species of butterflies which are distributed throughout most of the world [15]
References
- ^ Kennedy, J. S. (1985) Migration, behavioural and ecological. In: Rankin, M. A. (ed. ) Migration: Mechanisms and Adaptive Significance. Contributions in Marine Science 27 (supplement), 5–26.
- ^ Taylor, L. R. (1974) Insect migration, flight periodicity and the. boundary layer. J. Anim. EcoL 43: 225-238.
- ^ Denno, R. F. (1994) The evolution of dispersal polymorphism in insects: the influence of habitats, host plants and mates. Researches on Population Ecology 36, 127–135.
- ^ Southwood, T. R. E. (1962) Migration of terrestrial arthropods in relation to habitat. Biological Review 37, 171–214.
- ^ Hanski, I. and Kuussaari, M. (1995) Butterfly metapopulation dynamics. In: Cappuccino, N. and Price, P. W. (eds) Population Dynamics: New Approaches and Synthesis. Academic Press, New York, pp. 149–171.
- ^ Srygley, R. B. , Oliveira, E. G. and Dudley, R. (1996) Wind drift compensation, flyways, and conservation of diurnal, migrant Neotropical Lepidoptera. Proceedings of the Royal Society of London B 263, 1351–1357.
- ^ Heran, H. and Lindauer, M. (1963) Windkompensation und Seitenwindkorrektur der Bienen beim Flug über Wasser. Zeitschrift für vergleichende Physiologie 47:39–55.
- ^ Oliveira, E. G. , Dudley, R. and Srygley, R. B. (1996) Evidence for the use of a solar compass by neotropical migratory butterflies. Bulletin of the Ecological Society of America 775, 332.
- ^ Hyatt, M. (1993) The use of sky polarization for migratory orientation by monarch butterflies. PhD thesis, University of Pittsburgh, Pittsburgh, Pennsylvania.
- ^ Baker, R. R. (1987) Integrated use of moon and magnetic compasses by the heart-and-dart moth, Agrotis exclamationis. Animal Behaviour 35, 94–101.
- ^ Jones, D. S. and MacFadden, B. J. (1982) Induced magnetization in the monarch butterfly Danaus plexippus (Insecta, Lepidoptera). Journal of Experimental Biology 96, 1–9.
- ^ Perez, S. M. , Taylor, O. R. and Jander, R. (1999) The effect of a strong magnetic field on monarch butterfly (Danaus plexippus) migratory behavior. Naturwissenschaften 86, 140–143.
- ^ Srygley, R. B. , Oliveira, E. G. and Dudley, R. (1996) Wind drift compensation, flyways, and conservation of diurnal, migrant Neotropical Lepidoptera. Proceedings of the Royal Society of London B 263, 1351–1357.
- ^ Williams, C. B. (1930) The Migration of Butterflies. Oliver & Boyd, Edinburgh.
- ^ Senthilmurugan B. Mukurthi National Park:A migratory route for butterflies. (Aug 2005) J. Bombay. Nat. Hist. Soc. 102 (2): pp 241-242.
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