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DIFFERENTIAL ENCAPSULATION OF TWO BATHYPLECTES PARASITOIDS AMONG ALFALFA WEEVIL STRAINS, HYPERA POSTICA (GYLLENHAL)

Published online by Cambridge University Press:  31 May 2012

Christopher M. Maund  and
T.H. Hsiao
Christopher M. Maund
Affiliation:
Department of Biology, Utah State University, Logan, Utah, USA 84322–5305
T.H. Hsiao*
Affiliation:
Department of Biology, Utah State University, Logan, Utah, USA 84322–5305
*
1 Author to whom correspondence should be addressed.
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Abstract

Encapsulation of Bathyplectes curculionis (Thomson) and B. anurus (Thomson) (Hymenoptera: Ichneumonidae) was investigated by dissecting parasitized larvae of three strains of the alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae). In laboratory studies, there was no encapsulation of B. curculionis in the western strain of the weevil, a significant level of encapsulation in the eastern strain of the weevil, and nearly complete encapsulation in the Egyptian strain of the weevil. The rickettsia, Wolbachia postica Hsiao and Hsiao, found only in the western strain, was not involved in encapsulation. Variation in encapsulation was due to biological differences between weevil strains. Encapsulation rates among field populations of the western and Egyptian weevils were lower than in the laboratory. Encapsulation rates of weevil populations from zones in which western and Egyptian strains overlap in southern Utah, and between eastern and western strains in Colorado, were intermediate to rates of parental strains. These results imply that B. curculionis effectiveness against the western alfalfa weevil will decline with mixing of weevil strains. Bathyplectes anurus did not evoke encapsulation and was able to develop equally well in all three weevil strains. Our findings illustrate the importance of investigating the compatibility between alfalfa weevil strains and their parasitoids in devising a sound biological control strategy.

Résumé

Le capsulage de Bathyplectes curculionis (Thomson) et de B. anurus (Thomson) (Hymenoptera : Ichneumonidae) a été étudié en excisant les larves parasitisées de trois lignées du charançon postiche de la lucerne, Hypera postica (Gyllenhal) (Coleoptera : Curculionidae). Pour les études du laboratoire, la lignée de l’ouest du charançon n’a pas été capsulée, celle de l’est a été capsulée significativement, et celle de l’Égypte a été capsulée presqu’entièrement. La rickettsie, Wolbachia postica Hsaio et Hsaio, trouvée uniquement à la lignée de l’ouest, n’a pas été impliquée au capsulage. La variation en capsulage a été occasionnée par des différences biologiques parmi les lignées du charançon. Dans les populations sur le terrain, le taux du capsulage de ¡a lignée de l’ouest et de celui de la lignée d’Égypte s’est avéré moindre que ceux signalés au laboratoire. Les taux de capsulage des populations de charançon des zones où la lignée de l’ouest et celle de l’Égypte chevauchent au sud de l’Utah et où la lignée de l’est et celle de l’ouest chevauchent au Colorado ont été d’une position intérmédiaire aux taux ancestraux. Ces résultats suggèrent que l’efficacité de B. curculionis comme parasitoïde contre le charançon postiche de la luzerne diminuera au fur et à mesure que les lignées de charançons se mélangent. Bathyplectes anurus n’a pas provoqué de capsulage et a pu se développer aussi bien dans toutes les trois lignées de charançon. Nos résultats démontrent l’importance d’étudier la compatibilité parmi les lignées de charançons de la luzerne et leurs parasitoïdes pour préparer une forte stratégie pour la lutte biologique.

Type
Articles
Information
The Canadian Entomologist , Volume 123 , Issue 1 , February 1991 , pp. 197 - 203
Copyright
Copyright © Entomological Society of Canada 1991

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