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Effect of host plant on moulting in the African armyworm Spodoptera exempta (Walk.) (Lepidoptera: Noctuidae) at constant temperature and humidity conditions

Published online by Cambridge University Press:  08 April 2017

Jacob G. Yarro
Jacob G. Yarro
Affiliation:
International Centre of Insect Physiology and Ecology (ICIPE), P.O. Box 30772, Nairobi, Kenya
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Abstract

There are five caterpillar instars in the life cycle of Spodoptera exempta (Walk.) when they feed upon star grass, Cynodon dactylon (L.) Pers., maize, Zea mais L. and Kikuyu grass, Pennisetum clandestinum 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 (Hochst.) 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.

Keywords

African armywormhost plantshead capsule widthsdistance between frontal setaevariation in the number of instars
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 6 , Issue 2 , April 1985 , pp. 171 - 175
Copyright
Copyright © ICIPE 1985

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