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Changes in the composition of the fauna associated with the cassava mealybug, Phenacoccus manihoti, following the introduction of the parasitoid Epidinocarsis lopezi

Published online by Cambridge University Press:  19 September 2011

P. Neuenschwander
Affiliation:
International Institute of Tropical Agriculture, Oyo Road, PMB 5320, Ibadan, Nigeria
W. N. O. Hammond
Affiliation:
International Institute of Tropical Agriculture, Oyo Road, PMB 5320, Ibadan, Nigeria
R. D. Hennessey
Affiliation:
Programme de Recherche Agricole et Vulgarisation, (RAV) B.P. 11635, Kinshasa, Zaire
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Abstract

Over 130 species of insects were found in association with the cassava mealybug (CM), Phenacoccus manihoti, and its newly introduced parasitoid Epidinocarsis lopezi in Africa. As the CM in SW Nigeria declined under the influence of E. lopezi, this introduced wasp maintained densities of 2.8–3 per CM-infested tip early in the dry season and 1.3–1.6 per infested tip late in the dry season, but declined overall from 1.3 to 0.2 per randomly collected tip within 1 year. The decline of CM led to a sharp reduction in numbers of indigenous coccinellids, particularly of Hyperaspis spp. and to a lesser extent of Exochomus sp., due to competition with E. lopezi for the common food source. Numerous species of other polyphagous predators and parasitoids of coccinellids were found in low numbers. Indigenous primary parasitoids, Anagyrus spp., were rare, but their 10 spp. of hyperparasitoids were often reared from E. lopezi, with Prochiloneurus spp. and Chartocerus spp. being the most common. Hyperparasitism declined from 41.3% in March 1983 to 16.9% in Dec 1984 and proved to be positively density-dependent. The effects of hyperparasitoids on this biological control programme are discussed.

Résumé

Quelque 130 espèces d'insectes associées à la cochenille du manioc, Phenacoccus manihoti Mat.-Ferr. (Hom., Pseudococcidae) et à son parasitoïde récemment introduit, Epidinocarsis lopezi (De Santi) (Hym., Encyrtidae) ont été répertoriées en Afrique. L'introduction de la guêpe E. lopezi a entrainé le recul de la cochenille du manioc dans le sud-ouest du Nigéria et l'établissement du parasitoïde à la densité de 2,8-3 individus par apex infesté de cochenilles en début de saison sèche et de 1,3–1,6 individus lors d'infestations plus tardives. On a observé une baisse rapide, de 1,3 à 0,2 individus par apex choisi au hasard, au bout d'un an. Elle fut immédiatement suivie d'une réduction substantielle du nombre de coccinellidés indigènes, en particulier Hyperaspis spp. et, à un degré moindre, Exochomus sp., en raison de la compétition avec E. lopezi pour une source alimentaire commune. De nombreuses espèces d'autres prédateurs polyphages et de parasitoïdes des coccinellidés furent recueillis en petites quantités. Si les parasitoïdes primaires indigènes, Anagyrus spp., s'étaient raréfiés, dix espèces des hyperparasitoïdes qui leur sont associés, Prochiloneurus spp. et Chartocerus spp. parmi les plus communes, furent souvent observées sur E. lopezi. On nota une diminution de l'hyperparasitisme de 41,3% en mars 1983 à 16.9% en décembre 1984 qui s'avéra dépendre étroitement de la densité. L'impact des hyperparasitoïdes sur ce programme de lutte biologique est abordé.

Type
Symposium XI: Africa-wide Biological Control Programme of Cassava Pests
Copyright
Copyright © ICIPE 1987

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