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Preliminary studies on egg-mass development in the Simulium damnosum Theobald complex (Diptera: Simuliidae)

Published online by Cambridge University Press:  19 September 2011

C. A. Kyorku  and
J. N. Raybould
C. A. Kyorku
Affiliation:
Department of Zoology, University of Ghana, Legon, Accra, Ghana
J. N. Raybould
Affiliation:
WHO Onchocerciasis Control Programme, c/o Public Health Laboratory, Volta River Authority, Akosombo, Ghana
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Abstract

Egg-masses of Simulium damnosum s.l. were investigated to explain the frequent presence of undeveloped eggs in the lower layers. Natural development within egg-masses depended on whether eggs were laid (a) all at once or (b) were added to on consecutive evenings. In the field where the development of eggs from situation (a) was followed, top layer (TL) eggs hatched in 2 days when unexposed bottom layer (BL) eggs were still white. BL eggs uncovered 12 hr after oviposition were undeveloped, then hatched in 3 days. BL (a) eggs uncovered after 5 days were still untanned and undeveloped but were not further investigated.

In the laboratory, portions of egg-masses—intact or with the BLs exposed—were incubated in Petri dishes with and without preceding KOH egg separation treatment, or in flowing water. Other samples of BL eggs were incubated at different O2 levels. In Petri dishes, most TL eggs hatched within 24 hr of setting up but exposed BL eggs hatched (if at all) after much delay in 6–14 days. No unexposed BL eggs hatched even after TLs above them had done so. Transfer to flowing water or KOH treatment increased hatching and reduced the delay. Hatch rates of exposed BL eggs rose from 2.7 to 63% with increased O2 levels.

Implications with regard to laboratory culture and control operations are discussed. Mortality of covered eggs could be a potent population regulating factor within and perhaps even between species of the S. damnosum complex.

Résumé

On a fait des recherches sur les masses d'oeufs du Simulium damnosum afin de trouver une explication à la présence fréquente d'oeufs non développés dans les couches inférieures. Le développement naturel au sein des masses d'oeufs dépendait du fait que les oeufs étaient pondus (a) tous d'un coup ou (b) au cours de plusieurs soirs. Dans l'étude de la situation (a), les couches supérieures (CS) ont vu leurs oeufs éclore en 2 jours, alors que les oeufs non exposés de la couche inférieure (CI) étaient encore blancs. Les oeufs de la CI découverts 12 heures après l'oviposition n'étaient pas développés, puis faisaient éclosion en 3 jours. Les oeufs de la CI (a) découverts au bout de 5 jours étaient encore sans couleur mais on n'a pas poussé les recherches plus avant.

Dans le laboratoire, des portions de masses d'oeufs—intactes ou bien dont les CI avaient été exposées—ont été incubées dans des récipients in petri avec ou sans traitement préalable de séparation KOH de l'oeuf, ou dans de l'eau courante. D'autres échantillons d'oeufs de la CI ont été incubés à différents niveaux d'O2. Les récipients in petri ont vu éclore la plupart des oeufs des CS dans les 24 heures mais les oeufs des CI, exposés, n'ont fait éclosion (lorsqu'ils l'ont fait) qu'après un retard de 6 à 14 jours. Aucun oeuf non exposé des CI n'a fait éclosion, même à la suite de l'éclosion des oeufs des CS au-dessus d'eux. Le transfert à de l'eau courante ou au traitement KOH a augmenté l'éclosion et diminué le retard. Les taux d'éclosion des oeufs exposés des CI est passé de 2,7 à 63% avec une augmentation des niveaux d'O2.

On discute des conséquences en ce qui concerne les opérations de culture et de contrôle en laboratoire. La mortalité des oeufs couverts devrait être un facteur de régulation de la population au sein de et même peut-être entre les espèces du complexe S. damnosum.

Keywords

Simulium damnosumegg-mass developmentpopulation regulating factorincubation experimentsdelayed hatchingoxygen deficiencySimulium damnosumdéveloppement des masses d'oeuffacteur de régulation de la populationexpériences d'incubationéclosion retardéemanque d'oxygène
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 8 , Issue 3 , June 1987 , pp. 311 - 316
Copyright
Copyright © ICIPE 1987

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