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A preliminary study on the pathogenicity of two isolates of nucleopolyhedroviruses infecting African bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Published online by Cambridge University Press:  28 February 2007

J.G. Ogembo*
Affiliation:
Laboratory of Biodynamics of Insect–virus Interactions, Graduate School of Bioagricultural Sciences, Nagoya University, 464-8601, Chikusa, Nagoya, Japan
E.C. Kunjeku
Affiliation:
Department of Biological Sciences, University of Zimbabwe, PO Box MP 167, Mt Pleasant, Harare, Zimbabwe:
S. Sithanantham
Affiliation:
International Centre of Insect Physiology and Ecology (ICIPE), PO Box 30 772, Nairobi, 00100, Kenya
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Abstract

Two isolates of nucleopolyhedroviruses (NPVs) from Kenya and South Africa were compared to Gemstar® (a commercial NPV) for their pathogenicity against the first four larval instars of Helicoverpa armigera (Hübner). The larvae were fed on droplets with the three virus products in concentrations of 0 (control), 6×102, 6×103, 6×104 and 6×105 occlusion bodies/μl. The bioassays showed that the median lethal dose (LD50) values of 23 and 631 occlusion bodies for the first and second instars, respectively, were comparable to those of Gemstar®. The LD50 values for the third and fourth instars were 3981 and 39,810 for the Kenyan isolate and 1288 and 25,119 for the South African isolate. There was a linear relationship between the log LD50, the larval age and the lethal time (LT50), which appeared to be dose dependent. This correlation constitutes a useful index for estimating susceptibility of larval populations. The LT50 increased from 2.8 to 11.9 days and 2.8 to 6.8 days, respectively, for the Kenyan and South African isolates, suggesting a slight increase of resistance with age within infected larvae.

Type
Short Communication
Copyright
Copyright © ICIPE 2005

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