A better understanding of environmental factors driving natural pest regulation is a major challenge for designing sustainable cropping systems. The objective of the present study was to assess the association between vegetation openness in traditional tree-crop agroforestry systems in Senegal, richness and abundance of vertebrates including insectivorous birds and bats, and their contribution to the natural regulation of crop pests. The millet head miner (MHM), Heliocheilus albipunctella (Lepidoptera, Noctuidae), a major constraint to increasing millet crop productivity in sub-Saharan Africa, was selected as a model system. Ten sites separated by at least one km from each other were selected in a 100 km² study area in the Peanut basin in Senegal. In each site, a pair of millet fields distant from at least 100 m each was selected according to a gradient of vegetation openness within a 100-m radius buffer with sampling plot (5 x 5 m) at the center. Nine insectivorous bird and bat species were recorded in millet fields over the 2017 cropping season and their predator status was confirmed by direct observation or DNA detection in fecal samples. Grain losses were reduced when panicles were accessible to birds and bats, confirming their net contribution to pest regulation. At a local scale, tree diversity and vegetation openness were important predictors of the abundance of insectivorous village weaver birds and greyheaded sparrows, respectively. Some tree species (soapberry trees and neems) indirectly contributed to natural regulation of the MHM likely by providing refuges to insectivorous vertebrates whereas other tree species (baobabs) provided disservices as possible refuges for the MHM moths. Further research is needed to better understand relationships between tree cover, food web interactions and natural pest suppression, so that specific conservation measures such as habitat management can be designed to improve pest control. Highlights Vertebrates, including birds and bats, are effective predators of the millet head miner. They contribute to natural pest control and reduction of millet grain loss. The abundance of insectivorous birds is enhanced by tree diversity at a local scale. The contribution of trees for natural pest control is species-dependent. Trees can serve as refuges for pest (eg. baobab/moths) and predators (eg. palm tree/bats or neem/village weavers).
The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith; Lepidoptera: Noctuidae), is an invasive pest that has recently become a major worldwide threat for maize production. Greatest crop yield reductions occur following damage by FAW larvae at early vegetative plant stages, between the first and second week after plant emergence. In this study, field and semi‐field experiments were carried out to assess the effect of cyantraniliprole‐based seed treatment on the protection of early stages of maize plants against FAW and the associated mechanisms. In the field, maize seed treatment using cyantraniliprole (Fortenza®) significantly reduced the percentage of infested seedlings (77%) and the percentage of seedlings with severe damage (86%) up to 3 weeks after emergence. In a choice situation, semi‐field experiments showed that gravid moths preferred to lay eggs on plants from untreated seeds (68%) rather than on plants from treated seeds. To the best of our knowledge, this is the first evidence that insecticide residues present in plant tissues deter oviposition of Noctuid moths. Seed treatment with cyantraniliprole also reduced plant infestation (65%) 10 days after artificial inoculation of neonate larvae at 3 weeks after plant emergence, reducing the severity of leaf damage (by 67%). Insecticide seed treatment is a relevant tool for the integrated pest management of the FAW in high‐value crops such as sweet corn, especially for reducing foliar applications of insecticides during the most susceptible stages of the crop, as far as the risk of impacts on non‐target organisms is low and no alternative biocontrol option is available.
A spectrofluorimetric method was developed to determine residues of two β-blockers, atenolol (AT) and bisoprolol fumarate (BF), in Senegal's natural waters. The electronic absorption and fluorescence spectral properties of both β-blockers were investigated in several organic solvent mixtures [e.g., MeOH/H2O (60/40 v/v), cyclodextrins (β-cyclodextrin, HP-β-CD], and in the presence of surfactants (SDS, Triton X, Tween 80). After optimization, satisfactory analytical figures of merit were obtained for the determination of both β-blockers: concentration linear dynamic range of over one to two orders of magnitude, limits of detection (LODs) from 1.3 to 5.4 ng/ml for BF and from 1.2 to 3.7 ng/ml for AT, limits of quantification (LOQs) from 4.5 to 18.1 ng/ml for BF and from 4.0 to 12.5 ng/ml for AT. Relative standard deviations (RSDs) were between 2.1 and 5.3 %, according to the β-blockers. The spectrofluorimetric method was applied to the analysis of fortified river water and wastewater (effluent) collected in Senegal and France and spiked with both β-blockers. It yielded good recovery values, from 93.3 to 107.8 % for AT and from 97.4 to 108.9 % for BF. Our results demonstrated the simplicity, rapidity, and sensitivity of the spectrofluorimetric method to quantify residues of β-blockers in environmental waters.
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