Spatial and probability distribution of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) in cotton: Systematic sampling, exact confidence intervals and sequential test

Field sampling plans are proposed for monitoring Helicoverpa armigera (Hübner) populations on cotton and for threshold insecticide treatment in sub-Saharan Africa. The geostatistical analysis of the spatial distribution of bollworms validates systematic sampling (along a diagonal for example); systematic sampling is easier to perform than random sampling. The same negative binomial distribution was observed in Burkina Faso and Cameroon under controlled conditions, with or without insecticide treatment. The low infestation levels prevented the use of the approximate methods of Iwao or Kuno. Hence, exact confidence intervals not available in the literature are presented in graph form. Sequential and fixed size sampling methods are presented. (Résumé d'auteur