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FACTORS AFFECTING INFECTIVITY OF VAIRIMORPHA NECATRIX (MICROSPORIDIA: NOSEMATIDAE) IN TRICHOPLUSIA NI (LEPIDOPTERA: NOCTUIAE)

Published online by Cambridge University Press:  31 May 2012

Wei Hsuang Chu  and
Robert P. Jaques
Wei Hsuang Chu
Affiliation:
Research Station, Agriculture Canada, Harrow, Ontario N0R 1G0
Robert P. Jaques
Affiliation:
Research Station, Agriculture Canada, Harrow, Ontario N0R 1G0
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Abstract

Ingested dosages of 10.9 and 16.5 spores of Vairimorpha necatrix (Kramer) 7 and 27 weeks old, respectively, killed 50% of third-instar larvae of the cabbage looper, Trichoplusia ni (Hübner). Time to death of 50% of larvae (LT50) decreased from 14 to 3 days with increases in dosage from 5 × 101 to 5 × 106 spores (2-week-old)/Iarva. The LT50 for 5 × 101 spores/larva increased from 14 to 25 days with storage of spores at 4°C for 2 and 93 weeks, respectively. Spores applied to soil lost little activity during cool weather but spores applied in summer were inactivated within 60 days. Desiccation or exposure to sunlight or artificial light inactivated the spores. Rate of development of disease was increased by feeding host larvae a diet containing increased proportions of casein or sucrose. The optimum temperature for disease development in T. ni was 25°C.

Résumé

Cinquante pourcent des larves du troisième stade de l’arpenteuse du chou, Trichoplusia ni (Hübner), sont mortes suite à l’ingestion de doses de 10.9 et 16.5 spores de Vairimorpha necatrix (Kramer) âgées de 7 à 27 semaines, respectivement. Le temps nécessaire pour tuer 50% des larves (TL50) a diminué de 14 à 3 jours avec une augmentation de la dose de 5 × 101 à 5 × 106 spores (âgées de 2 sem.)/larve. Le TL50 à la dose 5 × 101 spores/larve est passé de 14 à 25 jours lorsque le temps d’entreposage des spores à 4°C fût prolongé de 2 à 93 semaines, respectivement. Les spores appliquées au sol sont restées actives par température froide, mais ont été inactivées en 60 jours lorsqu’appliquées durant l’été. La dessiccation ou l’exposition au soleil ou à la lumière artificielle ont rendu les spores inactives. La maladie s’est développée plus rapidement lorsque les larves infectées étaient nourries d’une diète contenant des proportions plus élevées de caséine ou de sucrose. La température optimale de développement de la maladie chez T. ni a été de 25°C.

Type
Articles
Information
The Canadian Entomologist , Volume 113 , Issue 2 , February 1981 , pp. 93 - 102
Copyright
Copyright © Entomological Society of Canada 1981

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