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Natural microsporidian infection in laboratory colonies of Spodoptera spp

Published online by Cambridge University Press:  19 September 2011

Ahlam A. Al Fazairy
Ahlam A. Al Fazairy
Affiliation:
Division of Entomology, Department of Plant Protection, Faculty of Agriculture, University of Alexandria, Alexandria, Egypt
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Abstract

Nosema sp. naturally occurred in both Spodoptera littoralis (Boisd.) and S. exigua (Hübner) laboratory colonies in Alexandria, Egypt (since November 1984). It was responsible for the dramatic suppression of their laboratory populations. Both young (3-day-old) and old (9-day-old) larvae of S. littoralis were susceptible to Nosema sp. However, the pathogen was more effective against the young larvae, especially at high doses, than the old ones. The estimated LC50 was 4.0 × 107 spores'ml, for 3-day-old larvae. The slope value was low (1.2) as typical of protozoan insect pathogens. Heavily infected 9-day-old larvae tended to die as larvae; while less infected ones either pupate or produce larval-pupal intermediate forms (12–23%). The developmental period of both infected larvae and pupae was increased by 4–6 and 3–5 days, respectively. The number of infected insects that reached the adult stage was decreased as the concentration of Nosema sp. spores was increased. Furthermore, infection was shown to reduce adult longevity and fecundity, and viability of the eggs. Larval faecal pellets harboured large numbers of viable spores. Transovum transmission of infection occurred. Two dipterous species, Culex pipiens and Aedes aegypti, were not susceptible to Nosema sp.

Résumé

L'infection des colonies laboratoires des deux espéces, Spodoptera littoralis (Boisd.) et Spodoptera exigua (Hübner) par le protozoaire Nosema sp. se produisit naturellement à Alexandrie, en Egypte (depuis Novembre 1984). Ce protozoaire fût responsable de la suppression dramatique de leurs populations au laboratoire. Les jeunes larves de 3 jours, ainsi que celles agées de 9 jours de S. littoralis furent sensibles à l'action pathogène de leur propre Nosema sp. (qui en fût isolé). En tous cas, le pathogène fût beaucoup plus efficace contre les jeunes larves, specialement aux doses elevées, que contre les larves plus agées. La valeur estimée de LC50 pour les larves de 3 jours fût de 4.0 × 107 spores'ml. La valeur de l'inclinaison (Slope) fût basse (1.2), comme typique des protozoaires pathogěnes d'insectes. Les larves agées de 9 jours sévèrement infectées, ont tendance a mourir sous forme larvaire, tandis que les moins atteintes ou bien se transforment en pupae, ou bien produisent des formes intermédiaires de larve- pupae (12–23%). La période de développement des larves et des pupaes infectées augmenta de 4–6 jours, respectivement. Le nombre des insectes infectés que atteignirent le stage adulte diminua, pendant que la concentration des spores de Nosema sp. augmenta. Aussi, on remarqua que l'infection diminuait la longevité, la fécondite, ainsi que la viabilité des oeufs. Les boulettes de déchets larvaire abritaient de grands nombres de spores, vivantes. La transmission transovarienne de l'infection se présente. Deux espèces de diptères, Culex pipiens et Aedes aegypti ne furent point sensibles au protozoaire Nosema sp.

Keywords

Nosema sp.Spodoptera littoralisSpodoptera exiguaCulex pipiensAedes aegyptisusceptibility testspathogenic effects
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 7 , Issue 6 , December 1986 , pp. 701 - 705
Copyright
Copyright © ICIPE 1986

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