Laboratory and field evaluation of a pyrethrum-based product (Agrothrin®) for the protection of stored beans from Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae) in Rwanda
2022
HATEGEKIMANA, Athanase | ERLER, Fedai
The bean bruchid, Acanthoscelides obtectus (Say) (Coleoptera: Chrysomelidae), a serious pest of kidney beans, Phaseolus vulgaris L., worldwide. In Rwanda, management of this pest in stored beans is generally based on conventional chemical insecticide applications with high residues. In this study, a pyrethrum-based product (Agrothrin®), a natural extract from the African pyrethrums with no side effects, was evaluated under laboratory and warehouse conditions. In both laboratory and warehouse assays, the product was tested at seven different doses ranging from 0.9 kg/ton to 2.1 kg/ton and compared with an untreated control and a conventional chemical insecticide control (malathion). The results showed that the insecticidal activity of Agrothrin® was low and not quick at lower doses and shorter exposure times, and higher doses ≥ 1.5 kg/ton and longer exposures > 2 weeks were needed to obtain an adult mortality more than 80%. In warehouse assays, the product gave effective bean seed protection against A. obtectus. The pest was predominantly present in positive (mean no. of living and dead beetles: 1.33 and 0.83/5 kg seed) and negative (mean no. of living and dead beetles: 2.50 and 3.33/5 kg seed) controls, but absent or in low number (mean no. of living and dead beetles: generally lower than 0.50/5 kg seed) in bean seeds treated with the product. Overall results suggest that Agrothrin® may be a very effective alternative to the existing conventional chemical insecticides in stored bean protection at doses equal to or higher than 1.7 kg/ton of seeds.
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