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PHYSICAL STRESSORS AFFECTING INTERACTIONS OF SPODOPTERA EXIGUA (HÜBNER) (LEPIDOPTERA: NOCTUIDAE) AND AN ENTOMOPATHOGENIC NEMATODE

Published online by Cambridge University Press:  31 May 2012

Graham S. Thurston  and
Harry K. Kaya
Graham S. Thurston
Affiliation:
Department of Nematology, University of California, Davis, California, USA 95616
Harry K. Kaya
Affiliation:
Department of Nematology, University of California, Davis, California, USA 95616
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Abstract

Cuticular damage of Spodoptera exigua (Hübner) pupae, caused by puncturing with a sterilized insect pin, resulted in enhanced susceptibility to the entomopathogenic nematode Steinernema carpocapsae (Weiser), but cold shock (5 °C for 24 h) did not alter susceptibility. The additional avenue of entry for the nematode probably accounted for the increased mortality of the damaged pupae. In all treatments, some dead pupae contained Xenorhabdus nematophilus (Poinar and Thomas), the symbiotic bacterium of S. carpocapsae, but no nematodes. More nematode-killed pupae containing X. nematophilus but no nematodes were found in the cold-shock treatment than in the room-temperature control (62.6 versus 46.9%). In contrast, fewer nematode-killed pupae containing X. nematophilus but no nematodes were found in the damaged pupae compared with the undamaged control (25.0 versus 45.1%). Moreover, mortality of nematodes within the cadavers of cold-shocked insects was higher than in the cadavers of non-cold-shocked insects. These results suggest that the stressors, cold shock and cuticular damage, produce fundamentally different responses in insects exposed to them, and that the physiological state of the insect greatly influences nematode survival in the host and hence nematode recycling in the environment.

Résumé

Des ponctions cuticulaires au moyen d’épingles entomologiques stérilisées ont augmenté la sensibilité de nymphes de Spodoptera exigua (Hübner) au nématode entomopathogène Steinernema carpocapsae (Weiser), mais un choc thermique (exposition à 5 °C pendant 24 h) n’a pas affecté leur sensibilité. Les voies d’entrée additionnelles créées par les ponctions sont probablement responsables de la mortalité accrue des nymphes endommagées. Dans toutes les expériences, certaines nymphes mortes contenaient des Xenorhabdus nematophilus (Poinar et Thomas), la bactérie symbiote de S. carpocapsae, mais ne contenaient pas de nématodes. Un plus grand nombre de nymphes tuées contenaient des X. nematophilus mais pas de nématodes chez le groupe soumis au froid que chez le groupe témoin gardé à la température ambiante (62,6 versus 46,9%). En revanche, il y avait moins de nymphes tuées contenant la bactérie mais pas de nématodes chez les nymphes endommagées que chez les nymphes témoins non endommagées (25,0 versus 45,1 %). De plus, la mortalité des nématodes dans les cadavres des insectes traités au froid était plus élevée que celle des nématodes trouvés dans les insectes non soumis au choc thermique. Ces résultats indiquent que les agents de stress, choc thermique et dommage cuticulaire, entraînent des réactions fondamentalement différentes chez les insectes qui les subissent et que la condition physiologique de l’insecte influence fortement la survie des nématodes chez leurs hôtes, et, par conséquent, le cycle des nématodes dans l’environnement.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 126 , Issue 2 , April 1994 , pp. 261 - 267
Copyright
Copyright © Entomological Society of Canada 1994

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