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Bioecological Aspects of the Mahogany Defoliator Heteronygmia dissimilis in Morogoro, Tanzania*

Published online by Cambridge University Press:  19 September 2011

H. G. Schabel ,
A. Schabel  and
H. P. Msanga
H. G. Schabel
Affiliation:
Faculty of Forestry, P.O. Box 3009, Sokoine University of Agriculture, Morogoro, Tanzania
A. Schabel
Affiliation:
Faculty of Forestry, P.O. Box 3009, Sokoine University of Agriculture, Morogoro, Tanzania
H. P. Msanga
Affiliation:
Faculty of Forestry, P.O. Box 3009, Sokoine University of Agriculture, Morogoro, Tanzania
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Abstract

Various aspects of the morphology, life cycle and several natural enemies of Heteronygmia dissimilis, a lymantriid defoliator of African mahogany, Khaya nyasica, were studied in Morogoro, Tanzania. This insect is a multivoltine species with at least four overlapping generations a year, all stages of which can be found from March to October. November to February are apparently spent in pupal aestivation. The September/October generation completed its life cycle from egg to adult in an average of 41 and 45 days for males (five moults) and females (six moults), respectively. On the average females produced 200 eggs. Larvae occurred in two colour variations. They are generally nocturnal feeders, skeletonizing leaflets while in the early instars and resting on foliage or bark during the day. Adults exhibit sexual dimorphism in terms of size, colour and shape. The sex factor was close to 0.5. Four species of hymenopterous parasites belonging to four families (Chalcidae, Encyrtidae, Eurytomidae and Ichneu-monidae), as well as two species of dipterous parasites (Tachinidae) were obtained from eggs, prepupae and pupae of H. dissimilis. During the rainy season, the entomopathogenic fungus Paecilomyces farinosus was epidemic among pupae.

Résumé

Des aspects variés de la morphologie, du cycle biologique et de plusieurs ennemis naturels d'Heteronygmia dissimilis (Lymantriidae), insect phyllophage de l'acajou d'Afrique, Khaya nyasica, ont été étudiées à Morogoro, Tanzanie. Cet insect est une espeèe d'au moins quatre générations par an, dont toutes les phases evolutives peuvent être observées de Mars à Octobre. De Novembre à Fevrier, l'insect apparaît dormant dans son état de pupe. En Novembre/Octobre la génération complétait son cycle biologique, soit de l'état d'oeuf à l'état adulte dans une moyenne de 41 jours (avec cinq mues) et 45 jours (avec six mues) respectivement pour les mâles et pour les femelles. En moyenne les femelles produisaient 200 oeufs. Les larves apparaissaient en deux colorations. En général, dans leurs premiers stades de dêveloppement les larves se nourissent pendant la nuit sur des folioles dont elles dévorent presque le tout à l'exception des veines majeures. Pendant la journée elles se reposent sur le feuillage ou sur l'écorce.

Les adultes montrent un dimorphisme sexuel accentué quant à la taille, la couleur et la forme. Le sexe ratio était près de 0.5. Quatre espéces parasites d'hymenoptères (Chalcidae, Encyrtidae, Eurytomidae et Ichneumonidae) ainsi que deux espèces de diptères (Tachinidae) ont été obtenues a partir des oeufs, prepupes et pupes d'H. dissimilis. Pendant la saison pluvieuse le champignon entomophyte Paecilomyces farinosus était épidemique parmi les pupes.

Keywords

Heteronygmia dissimilisKhaya nyasicalife cycleparasitesmycosisPaecilomyces farinosus.
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 9 , Issue 2 , April 1988 , pp. 179 - 184
Copyright
Copyright © ICIPE 1988

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