Abstract
Pathogenicity ofHeliothis nuclear polyhedrosis virus (HSNPV) to the corn earworm,Heliothis armigera, was studied using 3 different inoculative methods. The LD50 values of 4th-instar larvae inoculated with corn-fed, diet-fed and inoculum-imbiding method were 1.85×106, 2.55×105 and 1,22×103 PIBs/larva, respectively. The inoculum-imbiding is more sensitive and convenient for inoculatingH. armigera with HSNPV. The HSNPV product, Elcar®, was highly pathogenic toH. armigera, the LD50 values of 2nd-, 3rd- and 4th-instar larvae being 27, 83 and 1,221 PIBs/larva, respectively, as measured by the inoculum-imbiding method. The mortality of 4th-instar larvae caused by HSNPV was increased, but the incubation period was shortened with higher incubation temperatures. However, the high temperature at 35°C caused a lower mortality, and a prolongation of the median lethal time (LT50). Stability and persistence of HSNPV preparations were better in January–February and April–May than in June–July and October–November periods when sprayed on corn silks under field conditions. The HSNPV was inactivated by weak alkaline dew (pH 8.1) collected from soybean leaves, but it remained active on those from corn, tomato and asparagus with pH 7.2–7.3. The artificial heavy rainfall of 242 mm/h for 30 min did not wash off HSNPV preparations sprayed on the corn silks.
Résumé
La pathogénie du virus de la polyédrose nucléaire d'Heliothis (HSNPV) vis-à-vis de la noctuelle du maïs,Heliothis armigera a été étudiée en employant 3 méthodes différentes d'inoculation. Les valeurs de la DL50 des 4e stades larvaires inoculés par la méthode de la nourriture sur maïs, de la nourriture sur milieu artificiel et de l'absorption directe de l'inoculum étaient: 1,85 106, 2,55 105 et 1,22 103 PIBs/larve respectivement. L'absorption directe est plus sensible et plus pratique pour inoculerH. armigera avec HSNPV. Le produit HSNPV, Elcar® était fortement pathogène enversH. armigera, les valeurs des DL50 pour les 2e, 3e et 4e stades larvaires étant, mesurées par la méthode d'absorption directe, 27, 83 et 1,221 PIBs/larve respectivement.
La mortalité des 4e stades larvaires causée par l'HSNPV, augmentait, mais la période d'incubation raccourcissait avec des températures plus fortes d'incubation. Cependant, la forte température de 35°C entraînait une mortalité plus faible et une prolongation du temps léthal médian (TL50). La stabilité et la persistance des préparations de HSNPV ont été meilleures en janvier-février et en avril-mai, qu'en juin-juillet et en octobre-novembre lors de traitements sur les soies des fleurs femelles dans les conditions des champs. L'HSNPV était inactivé par la sécrétion faiblement alcaline (pH=8,1) récoltée des feuilles de soja, mais il restait actif sur celles issues du maïs, de la tomate et de l'asperge avec des pH de 7,2–7,3. La forte pluie artificielle de 242 mm/h durant 30 minutes n'entraînait pas les préparations de HSNPV appliquées sur les soies des fleurs femelles.
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Tuan, S.J., Tang, L.C. & Hou, R.F. Factors affecting pathogenicity of NPV preparations to the corn earworm,Heliothis armigera . Entomophaga 34, 541–549 (1989). https://doi.org/10.1007/BF02374392
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DOI: https://doi.org/10.1007/BF02374392