Assessing the role of non-cotton refuges in delaying Helicoverpa armigera resistance to Bt cotton in West Africa.

Non-cotton host plants without Bacillus thuringiensis (Bt) toxins can provide refuges that delay resistance to Bt cotton in polyphagous insect pests. It has proven difficult, however, to determine the effective contribution of such refuges and their role in delaying resistance evolution. Here, we used biogeochemical markers to quantify movement of Helicoverpa armigera moths from non-cotton hosts to cotton fields in three agricultural landscapes of the West African cotton belt (Cameroon) where Bt cotton was absent.

Inheritance and stability of pyrethroid resistance in the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae) in Central Africa.

Background: The cotton bollworm Helicoverpa armigera (Hübner) has developed esterase-mediated resistance to pyrethroids in Central Africa. To gain a better understanding of how quickly this resistance can evolve, its genetic basis and stability were examined in a field-derived strain of H. armigera (474-fold resistant to cypermethrin).

Esterase-mediated resistance to pyrethroids in field populations of Helicoverpa armigera (Lepidoptera: Noctuidae) from Central Africa.

Background: Evolution of pyrethroid resistance in the cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) threatens continued cotton production in Central Africa. Dose-response bioassays were conducted on area-wide collection of bollworm populations from major host plants, while biochemical techniques were used to evaluate basic mechanisms underlying resistance.

Results: Pyrethroid resistance is primarily associated with detoxification by enhanced esterase activity.

Genetic structure of the polyphagous pest Helicoverpa armigera (Lepidoptera: Noctuidae) across the Sub-Saharan cotton belt.

The cotton bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a key pest of various cropping systems in West and Central Africa, and developed insecticide resistance recently. To understand how such insecticide resistance expands across the region, the genetic structure of bollworm populations was studied using microsatellite markers. At first, the study was performed within several populations from Northern Cameroon: during one year, 19 populations (504 larvae) were sampled in different locations, dates and host plants (6 villages, 6 dates, 5 host plants).

Tracking pyrethroid resistance in the polyphagous bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae), in the shifting landscape of a cotton-growing area.

In cotton-growing areas of Central Africa, timing of host crops and pest management practices in annual rainfed cropping systems result in a shifting mosaic of habitats that influence the dynamics and resistance of Helicoverpa armigera (Hübner) populations on spatial scales, both within and across seasons. From 2002 to 2006, regional and local resistance was monitored among cotton fields and among the major host plants of the bollworm. From 2002, pyrethroid resistance increased within and across cotton-growing seasons to reach a worrying situation at the end of the 2005 growing season.

Using stable isotopes to trace origin and host plants of an African polyphagous pest and an European beneficial insect.

Crop protection against insect pests requires first a good knowledge of the biology and ecology of the different pest species and the associated beneficials, in particular the spatial distribution of the populations. But the movement of insect populations in the landscape remains often poorly known and in some cases does not make it possible to know the role of the various cultivated and wild habitats in the dynamics of pest and useful insects. Stable isotopes are a tool contributing to the knowledge of host plants (13carbon/12carbon) as well as geographical origin of insects (1hydrogen/2hydrogen).