Photobiology pp 389-416 | Cite as

Photoperiodism in Insects and Other Animals

  • David Saunders


Many animals, particularly those living at higher latitudes, use information from day length (or night length) to regulate seasonally appropriate behavioral and developmental strategies. The most common of these are the onset of overwintering diapause in the insects, and seasonal breeding strategies in many animal groups. This chapter examines the role of light in these processes: the photoreceptive “input pathway” to the photoperiodic clock, whether that clock is a function of the circadian system, its relationship to overt behavioral circadian rhythms and, in insects, its endocrine output to diapause or continuous summer development. Major models for the photo- periodic clock are described and evaluated, particularly whether apparent hourglass-like responses represent a distinct non-circadian clock or merely a variant of a circadian-based mechanism in which constituent oscillators “damp” rather rapidly in extended periods of darkness. Finally, some recent developments in unraveling the molecular genetics of the photoperiodic response are described.


Circadian System Photoperiodic Response Circadian Time Phase Response Curve Diapause Induction 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Baker, J.R. and Ranson, R.M. (1932) Factors affecting the breeding of the field mouse (Microtus agrestis): I. Light. Proc. Roy. Soc. London B 110, 313–322.Google Scholar
  2. Belozerov, V.N. (1964) Larval diapause in the tick Ixodes ricinus L., and its relation to external conditions. Zool. Zh. 43, 1626–1637 (In Russian).Google Scholar
  3. Bissonnette, T.H. (1932) Modification of mammalian seasonal cycles. Reactions of ferrets (Putorius vulgaris) of both sexes to electric light added after dark in November and December. Proc. Roy. Soc. London B 110, 322–336.Google Scholar
  4. Bowen, M.F., Saunders, D.S., Bollenbacher, W.E. and Gilbert, L.I. (1984) In vitro reprogramming of the photoperiodic clock in an insect brain-retrocerebral complex. Proc. Natl Acad. Sci. USA 81, 5881–5884.Google Scholar
  5. Bünning, E. (1936) Die endogene Tagesrhythmik als Grundlage der photoperiodischen Reaktion. Ber. Dtsch. Bot. Ges. 54, 590–607.Google Scholar
  6. Bünning, E. (1960) Circadian rhythms and time measurement in photoperiodism. Cold Spring Harbor Symp. Quant. Biol. 25, 249–256.Google Scholar
  7. Bünning, E. (1964) The physiological clock. Springer-Verlag, Berlin.Google Scholar
  8. Bünsow, R.C. (1953) Uber tages- und jahresrhythmische Anderungen der photoperiodischen Lichteropfindlichkeit bei Kalanchoe blossfeldiana und ihre Beziehungen zur endogonen Tagesrhythmik. Zschr. Botanik 41, 257-276.Google Scholar
  9. Claret, J. (1966) Mise en evidence du role photorecepteur lors de l’induction de la diapause chez Pieris brassicae (Lepido.). Ann. d’Endocrinologie 27, 311–320.Google Scholar
  10. Claret, J. (1989) Vitamine A et induction photoperiodique ou thermoperiodique de la diapause chez Pieris brassicae. C. R. Acad. Sci. Paris 308, 347–352.Google Scholar
  11. Claret, J. and Volkoff, N. (1992) Vitamin A is essential for the two processes involved in the photoperiodic reaction in Pieris brassicae. J. Insect Physiol. 38, 569–574.CrossRefGoogle Scholar
  12. Danks, H.V. (1987) Insect dormancy: An ecological perspective. Biological Survey of Canada (Terrestrial Arthropods), Monograph Series 1, Ottawa.Google Scholar
  13. Dawson, A., King, V.M., Bentley, G.E. and Ball, G.F. (2001) Photoperiodic control of seasonality in birds. J. Biol. Rhythms 16, 365–380.PubMedCrossRefGoogle Scholar
  14. Denlinger, D.L. (1971) Embryonic determination of pupal diapause in the flesh fly Sarcophaga crassipalpis. J. Insect Physiol. 17, 1815–1822.PubMedCrossRefGoogle Scholar
  15. Denlinger, D.L. (1985) Hormonal control of diapause. In: G.A. Kerkut and L.I. Gilbert (Eds.), Comprehensive insect physiology, biochemistry and pharmacology, vol. 8. Pergamon Press, Oxford, pp. 353–412.Google Scholar
  16. Denlinger, D.L. (1991) Relationship between cold hardiness and diapause. In: Insects at Low Temperature, R.E. Lee Jr. and D.L. Denlinger (Eds.), Chapman & Hall, New York, pp. 174–198.Google Scholar
  17. Dumortier, B. and Brunnarius, J. (1989) Diet-dependent switch from circadian to hourglass-like operation of an insect photoperiodic clock. J. Biol. Rhythms 4, 481–490.PubMedCrossRefGoogle Scholar
  18. Elliott, J.A. (1976) Circadian rhythms and photoperiodic time measurement in mammals. Federation Proc. 35, 2339–2346.Google Scholar
  19. Ferenz, H.J. (1975) Photoperiodic and hormonal control of reproduction in male beetles, Pterostichus nigrita. J. Insect Physiol. 21, 331–341.CrossRefGoogle Scholar
  20. Gao, N., Von Schantz, M., Foster, R.G. and Hardie, J. (1999) The putative brain photoperiodic photoreceptors in the vetch aphid, Megoura viciae. J. Insect Physiol. 45, 1011–1019.PubMedCrossRefGoogle Scholar
  21. Garner, W.W. and Allard, H.A. (1920) Effect of the relative length of the day and night and other factors on growth and reproduction in plants. J. Agric. Res. 18, 553–606.Google Scholar
  22. Goldman, B. D. (2001) Mammalian photoperiodic systems: Formal properties and neuroendocrine mechanisms of photoperiodic time measurement. J. Biol. Rhythms 16, 283–301.Google Scholar
  23. Hamner, W.M. (1963) Diurnal rhythms and photoperiodism in testicular recrudescence of the house finch. Science 142, 1294–1295.PubMedCrossRefGoogle Scholar
  24. Hardie, J. (1990) The photoperiodic counter, quantitative day-length effects and scotophase timing in the vetch aphid Megoura viciae. J. Insect Physiol. 36, 939–949.CrossRefGoogle Scholar
  25. Hasegawa, K. and Shimizu, I. (1987) In vivo and in vitro photoperiodic induction of diapause using isolated brain-suboesophageal ganglion complexes of the silkworm, Bombyx mori. J. Insect Physiol. 33, 959–966.CrossRefGoogle Scholar
  26. Helfrich-Förster, C. (2001) The locomotor activity rhythm of Drosophila melanogaster is controlled by a dual oscillator system. J. Insect Physiol. 47, 877–887.CrossRefGoogle Scholar
  27. Hillman, W.S. (1964) Endogenous circadian rhythms and the response of Lemna perpusilla to skeleton photoperiods. Am. Naturalist 98, 323–328.Google Scholar
  28. Johnsson, A. and Karlsson, H.G. (1972) A feedback model for biological rhythms. I—Mathematical description and basic properties of the model. J. Theor. Biol. 36, 153–174.PubMedCrossRefGoogle Scholar
  29. Joosse, J. (1984) Photoperiodicity, rhythmicity and endocrinology of reproduction in the snail Lymnaea stagnalis. In: Photoperiodic regulation of insect and molluscan hormones. Ciba Foundation Symposium 104, pp. 204–220.Google Scholar
  30. Kimura, Y. and Masaki, S. (1993) Hourglass and oscillator expression of photoperiodic diapause response in the cabbage moth Mamestra brassicae. Physiol. Entomol. 18, 240–246.Google Scholar
  31. Kogure, M. (1933) The influence of light and temperature on certain characters of the silk-worm, Bombyx mori. J. Dept Agriculture, Kyushu University 4, 1–93.Google Scholar
  32. Konopka, R., Pittendrigh, C.S. and Orr, D. (1989) Reciprocal behaviour associated with altered homeostasis and photosensitivity of Drosophila clock mutants. J. Neurogenetics 6, 1–10.Google Scholar
  33. Koštàl, V. (2006) Eco-physiological phases of insect diapause. J. Insect Physiol. 52, 113–127.PubMedCrossRefGoogle Scholar
  34. Lankinen, P. (1986) Geographical variation in circadian eclosion rhythms and photo- periodic adult diapause in Drosophila littoralis. J. Comp. Physiol. A 159, 123–142.CrossRefGoogle Scholar
  35. Lankinen, P. and Forsman, P. (2006) Independence of genetic geographical variation between photoperiodic diapause, circadian eclosion rhythm, and Thr-Gly repeat region of the period gene in Drosophila littoralis. J. Biol. Rhythms 21, 1–10.Google Scholar
  36. Lees, A.D. (1953) The significance of the light and dark phases in the photoperiodic control of diapause in Metatetranychus ulmi Koch. Ann. Appl. Biol. 40, 487–497.CrossRefGoogle Scholar
  37. Lees, A.D. (1964) The location of the photoperiodic receptors in the aphid Megoura viciae. J. Exp. Biol. 41, 119–133.PubMedGoogle Scholar
  38. Lees, A.D. (1966) Photoperiodic timing mechanisms in insects. Nature 210, 986–989.PubMedCrossRefGoogle Scholar
  39. Lees, A.D. (1971) The relevance of action spectra in the study of insect photoperiodism. In: M. Menaker (Ed.), Biochronometry. National Academy of Science, Washington, DC, pp. 372–380.Google Scholar
  40. Lees, A.D. (1973) Photoperiodic time measurement in the aphid Megoura viciae. J. Insect Physiol. 19, 2279–2316.CrossRefGoogle Scholar
  41. Lewis, R.D. (2002) Quantitative models for insect clocks. In: D.S. Saunders (Ed.), Insect clocks, 3rd ed. Elsevier, Amsterdam, pp. 213–243.Google Scholar
  42. Lewis, R.D. and Saunders, D.S. (1987) A damped circadian oscillator model of an insect photoperiodic clock. I. Description of the model based on a feedback control system. J. Theor. Biol. 128, 47–59.Google Scholar
  43. Lumme, J. (1978) Phenology and photoperiodic diapause in northern populations of Drosophila. In H. Dingle (Ed.) Evolution of Insect Migration and Diapause, pp. 145–170. Springer-Verlag, New York.Google Scholar
  44. Marcovitch, S. (1923) Plant lice and light exposure. Science 58, 537–538.PubMedCrossRefGoogle Scholar
  45. Marcovitch, S. (1924) The migration of the Aphididae and the appearance of the sexual forms as affected by the relative length of daily light exposure. J. Agric. Res. 27, 513–522.Google Scholar
  46. Masaki, S. (1984) Unity and diversity in insect photoperiodism. In: Photoperiodic regulation of insect and molluscan hormones. Ciba Foundation symposium 104, 7–25.Google Scholar
  47. Nishizuka, M., Azuma, A. and Masaki, S. (1998) Diapause response to photoperiod and temperature in Lepisma saccharina Linnaeus (Thysanura: Lepismatidae). Entomol. Sci. 1, 7–14.Google Scholar
  48. Numata, H. and Hidaka, T. (1987) Photoreceptors for photoperiodism in the bean bug, Riptortus clavatus. Rostria 38, 571–580.Google Scholar
  49. Pittendrigh, C.S. (1966) The circadian oscillation in Drosophila pseudoobscura pupae: a model for the photoperiodic clock. Zschr. Pflanzenphysiol. 54, 275–307.Google Scholar
  50. Pittendrigh, C.S. (1972) Circadian surfaces and the diversity of possible roles of circadian organization in photoperiodic induction. Proc.Natl Acad. Sci. USA 69, 2734–2737.PubMedCrossRefGoogle Scholar
  51. Pittendrigh, C.S. and Minis, D.H. (1964) The entrainment of circadian oscillations by light and their role as photoperiodic clocks. Am. Naturalist 98, 261–294.CrossRefGoogle Scholar
  52. Richard, D.S., Watkins, N.L., Serafin, R.B. and Gilbert, L.I. (1998) Ecdysteroids regulate yolk protein uptake by Drosophila melanogaster oocytes. J. Insect Physiol. 44, 637–644.PubMedCrossRefGoogle Scholar
  53. Rieger, D., Stanewsky, R. and Helfrich-Förster, C. (2003) Cryptochrome, compound eyes, Hofbauer-Buchner eyelets, and ocelli play different roles in the entrainment and masking pathway of the locomotor activity rhythm in the fruit fly Drosophila melanogaster. J. Biol. Rhythms 18, 377–391.PubMedCrossRefGoogle Scholar
  54. Rowan, W. (1926) On photoperiodism, reproductive periodicity and the annual migration of birds and certain fishes. Proc. Boston Soc. Natural History 38, 147–189.Google Scholar
  55. Sabrosky, C.W., Larson, I. and Nabours, R.K. (1933) Experiments with light upon reproduction, growth and diapause in grouse locusts. Trans. Kansas Acad. Sci. 36, 298–300.CrossRefGoogle Scholar
  56. Saunders, D.S. (1966) Larval diapause of maternal origin—II. The effect of photoperiod and temperature on Nasonia vitripennis. J. Insect Physiol. 12, 569–581.CrossRefGoogle Scholar
  57. Saunders, D.S. (1973) The photoperiodic clock in the flesh-fly, Sarcophaga argyrostoma. J. Insect Physiol. 19, 1941–1954.PubMedCrossRefGoogle Scholar
  58. Saunders, D.S. (1974) Evidence for ‘dawn’ and ‘dusk’ oscillators in the Nasonia photoperiodic clock. J. Insect Physiol. 20, 77–88.CrossRefGoogle Scholar
  59. Saunders, D.S. (1975) ‘Skeleton’ photoperiods and the control of diapause and development in the flesh-fly, Sarcophaga argyrostoma. J. Comp. Physiol. 97, 97–112.CrossRefGoogle Scholar
  60. Saunders, D.S. (1978) An experimental and theoretical analysis of photoperiodic induction in the flesh-fly Sarcophaga argyrostoma. J. Comp. Physiol. 124, 75–95.CrossRefGoogle Scholar
  61. Saunders, D.S. (1979) External coincidence and the photoinducible phase in the Sarcophaga photoperiodic clock. J. Comp. Physiol. 132, 179–189.CrossRefGoogle Scholar
  62. Saunders, D.S. (1981) Insect photoperiodism: the clock and the counter. Physiol. Entomol. 6, 99–116.Google Scholar
  63. Saunders, D.S. (1982) Photoperiodic induction of pupal diapause in Sarcophaga argyrostoma: temperature effects on circadian resonance. J. Insect Physiol. 28, 305–310.CrossRefGoogle Scholar
  64. Saunders, D.S. (1986) Many circadian oscillators regulate developmental and behavioural events in the flesh fly Sarcophaga argyrostoma. Chronobiol. Int. 3, 71–83.PubMedCrossRefGoogle Scholar
  65. Saunders, D.S. (1987) Maternal influence on the incidence and duration of larval diapause in Calliphora vicina. Physiol. Entomol. 12, 331–338.Google Scholar
  66. Saunders, D.S. (1990) The circadian basis of ovarian diapause regulation in Drosophila melanogaster: is the period gene causally involved in photoperiodic time measurement? J. Biol. Rhythms 5, 315–331.PubMedCrossRefGoogle Scholar
  67. Saunders, D.S. (1992) The photoperiodic clock and “counter” in Sarcophaga argyrostoma: experimental evidence consistent with “external coincidence” in insect photoperiodism. J. Comp. Physiol. 170, 121–127.CrossRefGoogle Scholar
  68. Saunders, D.S. (1997) Insect circadian rhythms and photoperiodism. Invertebrate Neurosci. 3, 155–164.CrossRefGoogle Scholar
  69. Saunders, D.S. (2000) Arthropoda – Insecta: Diapause. In: A. Dorn (Ed.), Reproductive biology of the invertebrates, Vol. X, Part B. John Wiley & Sons Ltd, Chichester, pp. 145–184.Google Scholar
  70. Saunders, D.S. (2002) Insect clocks, 3rd ed. Elsevier, Amsterdam.Google Scholar
  71. Saunders, D.S. (2005) Erwin Bünning and Tony Lees, two giants of chronobiology, and the problem of time measurement in insect phtoperiodism. J. Insect Physiol. 51, 599–608.PubMedCrossRefGoogle Scholar
  72. Saunders, D.S. and Cymborowski, B. (1996) Removal of optic lobes of adult blow flies (Calliphora vicina) leaves photoperiodic induction of larval diapause intact. J. Insect Physiol. 42, 807–811.CrossRefGoogle Scholar
  73. Saunders, D.S. and Cymborowski, B. (2003) Selection for high diapause incidence in blow flies (Calliphora vicina) maintained under long days increases the maternal critical daylength: some consequences for the photoperiodic clock. J. Insect Physiol. 49, 777–784.PubMedCrossRefGoogle Scholar
  74. Saunders, D.S. and Gilbert, L.I. (1990) Regulation of ovarian diapause in the fruit fly Drosophila melanogaster by photoperiod at moderately low temperature. J. Insect Physiol. 36, 195–200.CrossRefGoogle Scholar
  75. Saunders, D.S. and Lewis, R.D. (1987a) A damped circadian oscillator model of an insect photoperiodic clock. II. Simulations of the shapes of the photoperiodic response curves. J. Theor. Biol. 128, 61–71.Google Scholar
  76. Saunders, D.S. and Lewis, R.D. (1987b) A damped circadian oscillator model of an insect photoperiodic clock. III. Circadian and “hourglass” responses. J. Theor. Biol. 128, 73–85.Google Scholar
  77. Saunders, D.S., Henrich, V.C. and Gilbert, L.I. (1989) Induction of diapause in Drosophila melanogaster: photoperiodic regulation and the impact of arrhythmic clock mutations on time measurement. Proc. Natl Acad. Sci. USA 86, 3748–3752.PubMedCrossRefGoogle Scholar
  78. Saunders, D.S., Gillanders, S.W. and Lewis, R.D. (1994) Light-pulse phase response curves for the locomotor activity rhythm in period mutants of Drosophila melanogaster. J. Insect Physiol. 40, 957–968.CrossRefGoogle Scholar
  79. Saunders, D.S., Lewis, R.D. and Warman, G.R. (2004) Photoperiodic induction of diapause: opening the black box. Physiol. Entomol. 29, 1–15.CrossRefGoogle Scholar
  80. Saunders, D.S., Richard, D.S., Applebaum, S.W., Ma, M. and Gilbert, L.I. (1990) Photo- periodic diapause in Drosophila melanogaster involves a block to the juvenile hormone regulation of ovarian maturation. Gen. Comp. Endocrin. 79, 174–184.CrossRefGoogle Scholar
  81. Shiga, S. and Numata, H. (1996) Effects of compound eye removal on the photoperiodic response of the band-legged ground cricket, Pteronemobius nigrofasciatus. J. Comp. Physiol. A 179, 625–633.Google Scholar
  82. Shiga, S. and Numata, H. (1997) Induction of reproductive diapause via perception of photoperiod through the compound eyes of the adult blow fly, Protophormia terraenovae. J. Comp. Physiol. A 181, 35–40.CrossRefGoogle Scholar
  83. Shimizu, I. (1982) Photoperiodic induction in the silkworm, Bombyx mori, reared on artificial diet: evidence for extraretinal photoreception. J. Insect Physiol. 28, 841–846.CrossRefGoogle Scholar
  84. Shimizu, I. and Hasegawa, K. (1988) Photoperiodic induction of diapause in the silkworm, Bombyx mori: location of the photoreceptor using a chemiluminescent paint. Physiol. Entomol. 13, 81-88.Google Scholar
  85. Shimizu, I. and Kato, M. (1984) Carotenoid functions in photoperiodic induction in the silkworm, Bombyx mori. Photobiochem. Photobiophys. 7, 47–52.Google Scholar
  86. Shimizu, I., Yamakawa, Y., Shimazaki, Y. and Iwasa, T. (2001) Molecular cloning of Bombyx cerebral opsin (Boceropsin) and cellular localization of its expression in the silkworm brain. Biochem. Biophys. Res. Commun. 287, 27–34.PubMedCrossRefGoogle Scholar
  87. Steel, C.G.H. and Lees, A.D. (1977) The role of neurosecretion in the photoperiodic control of polymorphism in the aphid Megoura viciae. J. Exp. Biol. 67, 117–135.PubMedGoogle Scholar
  88. Stoleru, D., Peng, Y., Agosto, J. and Rosbash, M. (2004) Coupled oscillators control morning and evening locomotor behaviour of Drosophila. Nature 431, 862–868.PubMedCrossRefGoogle Scholar
  89. Stoleru, D., Peng, Y., Nawathean, P. and Rosbash, M. (2005) A resetting signal between Drosophila pacemakers synchronizes morning and evening activity. Nature 438, 238–242.PubMedCrossRefGoogle Scholar
  90. Stross, R.G. and Hill, J.C. (1968) Photoperiod control of winter diapause in the fresh water crustacean, Daphnia. Biol. Bull. Marine Biological Lab., Woods Hole 134, 176–198.CrossRefGoogle Scholar
  91. Takeda, M. (1978) Photoperiodic time measurement and seasonal adaptation of the South-western corn borer, Diatraea grandiosella Dyar (Lepidoptera: Pyralidae). Ph.D. thesis, University of Missouri–Columbia.Google Scholar
  92. Tauber, M.J., Tauber, C.A. and Masaki, S. (1986) Seasonal adaptations of insects. Oxford University Press, Oxford.Google Scholar
  93. Thiele, H-U. (1977) Differences in measurement of daylength and photoperiodism in two stocks from sub-arctic and temperate climates in the carabid beetle, Pterostichus nigrita F. Oecologia (Berlin) 30, 349–365.CrossRefGoogle Scholar
  94. Underwood, H. and Goldman, B.D. (1987) Vertebrate circadian and photoperiodic systems: role of the pineal gland and melatonin. J. Biol. Rhythms 2, 279–315.PubMedCrossRefGoogle Scholar
  95. Van Zon, A.Q., Overmeer, W.P.J. and Veerman, A. (1981) Carotenoids are functionally involved in photoperiodic induction of diapause in a predacious mite. Science 213, 1131–1133.CrossRefGoogle Scholar
  96. Vaz Nunes, M. and Saunders, D.S. (1999) Photoperiodic time measurement in insects: a review of clock models. J. Biol. Rhythms 14, 84–104.PubMedCrossRefGoogle Scholar
  97. Vaz Nunes, M. and Veerman, A. (1982) Photoperiodic time measurement in the spider mite Tetranychus urticae: A novel concept. J. Insect Physiol. 28, 1041–1053.CrossRefGoogle Scholar
  98. Vaz Nunes, M., Kenny, N.A.P. and Saunders, D.S. (1990) The photoperiodic clock in the blowfly Calliphora vicina. J. Insect Physiol. 36, 61–67.CrossRefGoogle Scholar
  99. Veerman, A. (1977) Aspects of the induction of diapause in a laboratory strain of the mite Tetranychus urticae. J. Insect Physiol. 23, 703–711.CrossRefGoogle Scholar
  100. Veerman, A. (1980) Functional involvement of carotenoids in photoperiodic induction of diapause in the spider mite, Tetranychus urticae. Physiol. Entomol. 5, 291–300.Google Scholar
  101. Veerman, A., Overmeer, W.P.J., Van Zon, A.Q., De Boer, J.M., De Waard, E.R. and Huisman, H.O. (1983) Vitamin A is essential for photoperiodic induction of diapause in an eyeless mite. Nature 302, 248–249.CrossRefGoogle Scholar
  102. Veerman, A., Slagt, M.E., Alderliest, M.F.J. and Veenendaal, R.L. (1985) Photoperiodic induction of diapause in an insect is vitamin A dependent. Experientia 41, 1194–1195.CrossRefGoogle Scholar
  103. Veerman, A. and Vaz Nunes, M. (1980) Circadian rhythmicity participates in the photo- periodic determination of diapause in spider mites. Nature 287, 140–141.CrossRefGoogle Scholar
  104. Veerman, A. and Vaz Nunes, M. (1987) Analysis of the operation of the photo- periodic counter provides evidence for hourglass time measurement in the spider mite Tetranychus urticae. J. Comp. Physiol. A 160, 421–430.CrossRefGoogle Scholar
  105. Vinogradova, E.B. and Zinovjeva, K.B. (1972) Maternal induction of larval diapause in the blowfly, Calliphora vicina. J. Insect Physiol. 18, 2401–2409.PubMedCrossRefGoogle Scholar
  106. Wayne, N. L. (2001) Regulation of seasonal reproduction in mollusks. Biol. Rhythms 16, 391–402.CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  • David Saunders

There are no affiliations available

Personalised recommendations