The potential of perimeter trap cropping, using short and extra-short duration pigeon pea (SD PP and ESD PP), sorghum and cotton, was evaluated in Niger as an agroecological alternative to pesticide application on okra for the management of the tomato fruit worm (TFW) Helicoverpa armigera (Hübner). In 2008, infestation by TFW and damage by fruit worms of unsprayed okra with SD PP borders was intermediate between cypermethrin-sprayed and unsprayed pure okra crops. In 2009, the cypermethrin-sprayed okra was significantly less damaged by fruit worms than in the unsprayed pure okra, as well as in the unsprayed okra crops with SD PP, sorghum and cotton borders. In 2010, the pure okra crop sprayed with cypermethrin was significantly less infested by TFW than the unsprayed pure okra crop and the unsprayed okra crop with SD PP borders. The unsprayed okra crop with ESD PP borders was intermediate between cypermethrin-sprayed and unsprayed pure okra crops. The slightly lower TFW infestation of the unsprayed okra crop with ESD PP borders was a result of increased top-down regulation by predator spiders, whose colonization was significantly higher on the unsprayed okra crop with ESD PP borders than on both (sprayed and unsprayed) pure okra crops. (Résumé d'auteur

a b s t r a c tFrom 2010 to 2011 in Niger, the effects of a wind erosion-alleviating practice, i.e. mulching pearl millet fields with crop residue, on populations of and damage induced by millet stem borer (MSB), head miner (MHM), and head scarab (MHS) were studied. Significant differences in the survival of MSB diapausing larvae in millet stems at the end of the dry season were found at both Sadore and Doukoudoukou. At Sadore, mean MSB larval survival in the treatment where stems were exported at harvest and stored on platforms (treatment 1) was 1.2/stem, i.e. significantly higher than in all other treatments. Survival was between 0.1 and 0.2 larva in treatments 2 (with millet stems left standing from harvest throughout the dry season) and 3 (with millet stems flattened toward the end of the dry season, four months after harvest). It was less than 0.1 larva in treatments 4 (with millet stems flattened in the middle of the dry season, two months after harvest) and 5 (with millet stems flattened at the beginning of the dry season, at harvest). At Doukoudoukou, mean MSB larval survival in treatment 1 was 0.14/stem, i.e. significantly higher than in treatments 4 and 5 (0.02-0.03 larva), with intermediary findings obtained in treatments 2 and 3 (0.04-0.08 larva). The population and biomass of diapausing MHM pupae and of MHS larvae in the soil were low at both locations, and not affected by crop residue management. Thus, crop residue management whereby stems were left standing until the end of the dry season did not enhance control of millet head pests via increased predator activity, while it increased MSB survival in stems.

From 2008 to 2010, the effect of a wind erosion-alleviating practice, that is, planting of windbreaks of the perennial grass Andropogon gayanus Kunth on the populations of millet stem borer (MSB) Coniesta ignefusalis (Hampson) (Lepidoptera: Pyralidae) and the damage induced by this pest to pearl millet, was studied at Sadore (Niger). The extent of bored stems in the A. gayanus hedge bordering millet plots (23% on average) was significantly lower than in the millet plots (76% on average), with no MSB larva recovered, compared to an average of 2.2 larvae per stem in the millet plots over the three years. Andropogon grass was thus ruled out as a trap crop for MSB management. Under the conditions of this study, a pest regulation service by Andropogon grass hedges, synergistic with a potential wind erosion alleviating service, cannot be put forward.