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MELANIZATION OF EGGS AND LARVAE OF THE PARASITOID, EPIDINOCARSIS LOPEZI (DE SANTIS) (HYMENOPTERA: ENCYRTIDAE), BY THE CASSAVA MEALYBUG, PHENACOCCUS MANIHOTI MATILE-FERRERO (HOMOPTERA: PSEUDOCOCCIDAE)

Published online by Cambridge University Press:  31 May 2012

Daniel J. Sullivan  and
Peter Neuenschwander
Daniel J. Sullivan
Affiliation:
Department of Biological Sciences, Fordham University, Bronx, New York, USA10458
Peter Neuenschwander
Affiliation:
International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria
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Abstract

The encyrtid wasp Epidinocarsis lopezi (De Santis) has been introduced into Africa as a biological control agent against the cassava mealybug Phenacoccus manihoti Matile-Ferrero. This host has a defense reaction against the immature parasitoid that involves encapsulation and melanization. Under laboratory conditions, 37.5% of once-stung cassava mealybugs had been parasitized, as indicated by eggs and larvae of the parasitoid in dissected hosts. Of these parasitized cassava mealybugs, 89.6% contained melanized particles (egg, partially melanized larva, internal host tissues, exoskeleton wound scars). Some of the parasitoid larvae were only partially melanized, and either freed themselves from the melanized capsule or else shed it at the next molt. By the 3rd day of their development only 12.5% were completely melanized. In cassava mealybugs with melanized host tissue but no living parasitoid, the survival of the host was not affected by the melanization. The mealybug itself sometimes shed black particles at the next molt and these were found attached to the cast skins. When superparasitized in the laboratory, 68.6% of twice-stung cassava mealybugs contained parasitoids. Mummies collected from a field experiment showed that melanization rates of mummies increased with increasing parasitization rates. Thus, melanization in the cassava mealybug was commonly triggered when E. lopezi oviposited, but this defense reaction was mostly ineffective, permitting the introduced parasitoid to be a successful biological control agent in Africa against the cassava mealybug, a major pest on this important food crop.

Résumé

La guêpe encyrtide Epidinocarsis lopezi (De Santis) a été introduite en Afrique comme agent biologique de répression de la cochenille du cassava Phenacoccus manihoti Matile-Ferrero. L’hôte fait une réaction de défense caractérisée par l’encapsulation et la mélanization du parasitoïde immature. Dans des conditions de laboratoire, 37,5% des cochenilles attaquées une seule fois étaient effectivement parasitées, tel qu’établi par la présence d’oeufs et de larves à la dissection. Parmi ces cochenilles parasitées, 89,6% contenaient des particules mélanisées (oeufs, larves partiellement mélanisées, tissus internes de l’hôte, cicatrices exosquelettiques). Certaines des larves du parasitoïdes étaient mélanisées seulement en partie, et se sont libérées elles-mêmes de la capsule mélanisée ou l’ont rejetée lors de la mue suivante. Au troisième jour du développement de ces larves, seulement 12,5% étaient entièrement mélanisées. La survie des cochenilles montrant des tissus mélanisés en l’absence d’un parasitoïde vivant n’était pas affectée par la mélanisation. La cochenille elle-même rejetait parfois des particules noires avec l’exuvie lors de la mue suivante. Parmi les cochenilles superparasitées suite à deux attaques au laboratoire, 68,6%, contenaient des parasitoïdes. La collection de momies sur le terrain a montré une augmentation de l’incidence de mélanisation des momies avec l’augmentation de l’incidence du parasitisme. Ainsi, la mélanisation est fréquente chez les cochenilles recevant des oeufs d’E. lopezi, mais cette réaction de défense est plutôt inefficace, permettant à cet agent biologique introduit en Afrique d’agir avec succès contre la cochenille du cassava, un ravageur primaire de cette culture importante comme ressource alimentaire.

Type
Articles
Information
The Canadian Entomologist , Volume 120 , Issue 1 , January 1988 , pp. 63 - 71
Copyright
Copyright © Entomological Society of Canada 1988

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