Effect of Host Plant on Moulting in the African Armyworm Spodoptera Exempta (Walk.) (Lepidoptera: Noctuidae) At Constant Temperature and Humidity Conditions

  • Jacob G. Yarro
Research Article


There are five caterpillar instars in the life cycle of Spodoptera Exempta (Walk.) when they feed upon star grass, Cynodon daciylon (L.) Pers., maize, Zea mais L. and Kikuyu grass, Pennisetum eland. Jtinum Chiov. at 25–30°C. When the temperature is 18°C, however, there was an additional instar in the cycle. Similarly extra instars are formed on Guinea grass, Panicum maximum Jacq., Setaria plicatilis (Höchst.) Hack, and a sedge, Cyperus maranguensis K. Schm. even when the temperature appears to be sufficiently high for normal development. Occasionally the additional sixth instar is also too small to pupate, in which case a seventh instar is formed. It appears that caterpillars on nutritionally inadequate host plants or those at low temperatures are being partially starved and must continue moulting until the appropriate size is attained or exceeded. Measurements of the head capsule widths or distances between the frontal clypeal setae suggest that only individuals reaching or exceeding a species specific threshold size pupate. Extra moults appear to be an adaptation to environmental fluctuations obtaining within the range of occurrence of S. exempta.

Key Words

African armyworm host plants head capsule widths distance between frontal setae variation in the number of instars 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Brown E. S. (1970) Control of the African army worm, Spodoptera Exempta (Walk.)—An appreciation of the problem. E. Afr. agric. For. J. 35, 237–245.CrossRefGoogle Scholar
  2. Brown E. S., Betts E. and Rainey R. C. (1969) Seasonal changes in distribution of the armyworm, Spodoptera Exempta (Walk.) (Lepidoptera, Noctuidae) with special reference to East Africa. Bull. ent. Res. 58, 661–728.CrossRefGoogle Scholar
  3. Brown E. S. and Swaine C. (1966) New evidence on the migration of moths of the African armyworm, Spodoptera Exempta (Walk.) (Lepidoptera, Noctuidae). Bull. ent. Res. 56, 671–684.CrossRefGoogle Scholar
  4. David W. A. L., Ellaby S. and Taylor G. (1975) The viability of eggs of the African armyworm, Spodoptera Exempta in laboratory cultures. Entomologia exp. appl. 18, 266–237.Google Scholar
  5. Gilbert L. I. and King D. S. (1973) Physiology of growth and development: endocrine aspects. In The Physiology of Insecta (Edited by Rockstain M.), Vol. 1, pp. 249–370. Academic Press, New York.CrossRefGoogle Scholar
  6. Hattingh C. C. (1941) The biology and ecology of the armyworm (Laphygma exempta) and its control in South Africa. Dep. Agric. S. Afr. Sci. Bull. 217, 1–50.Google Scholar
  7. Matthee J. J. (1946) A study of the phases of the armyworm (Laphygma exempta Walk.). J. ent. Soc. sth. Afr. 9, 60–77.Google Scholar
  8. Nijhout H. F. (1975) A threshold size for metamorphosis in the tobacco hornworm Manduca sexta L. Biol. Bull. 49, 214–225.CrossRefGoogle Scholar
  9. Nijhout H. F. and Williams C. M. (1974) Control of moulting and metamorphosis in the tobacco hornworm, Manduca sexta (L). Cessation of juvenile hormone secretion as a trigger for pupation. J. exp. Biol. 61, 493–501.PubMedGoogle Scholar
  10. Odiyo P. O. (1981) Development of the first outbreaks of the African armyworm, Spodoptera Exempta (Walk.) between Kenya and Tanzania during the “off season” months of July to December. Insect Sci. Applic. 1, 305–318.Google Scholar
  11. Patel N. and Mathivan K. (1969) Effect of hormones on RNA and Protein synthesis in the imaginai wing discs of the ricini silkworm. J. Insect Physiol. 15, 2141–2150.CrossRefGoogle Scholar
  12. Pipa R. L. (1976) Supernumerary instars produced by chilled wax moth larvae: Endocrine mechanisms. J. Insect Physiol. 22, 1641–1647.CrossRefGoogle Scholar
  13. Podoler H. and Klein M. (1978) Distance between frontal setae. A new tool for determining caterpillar instars. J. nat. Hist. 12, 341–347.CrossRefGoogle Scholar
  14. Rose D. J. W. (1975) Field development and quality changes in successive generations of Spodoptera Exempta Walk., the African armyworm. J. appl. Ecol. 12, 727–739.CrossRefGoogle Scholar
  15. Rose D. J. W. (1979) The significance of low density populations of the African armyworm, Spodoptera Exempta (Walk,). Phil, trans. R. Soc. Lond. B237, 393–402.CrossRefGoogle Scholar
  16. Wilde J. de, Kort C. A. D. de and Loof A. de (1971) the significance of juvenile hormone titres. Mitt. Schweiz, ent. Gesellsch. 44, 79–86.Google Scholar
  17. Wigglesworth V. B. (1970) Insect Hormones. Freeman, San Francisco.Google Scholar
  18. Yarro J. G. (1984) Survival and development of the African armyworm, Spodoptera Exempta (Walk.) on some grass species (Gramineae). Insect Sci. Applic. 5, 1–5.Google Scholar

Copyright information

© ICIPE 1985

Authors and Affiliations

  • Jacob G. Yarro
    • 1
  1. 1.International Centre of Insect Physiology and Ecology (ICIPE)NairobiKenya

Personalised recommendations