Population dynamics and seed yield losses by the gram caterpillar (Helicoverpa armigera) in rabi forage legumes

摘要

Gram caterpillar, Helicoverpa armigera (Hubner) (Noctuidae: Lepidoptera) is a major threat to agriculture in Africa, Asia, Oceania and parts of Europe. The pest has a preference for feeding on the floral parts of host plants especially forage and grain legumes. H. armigera is the key pest of Egyptian clover (Berseem) seed crop in northern India. Other Rabi forage legumes like Persian clover (Shaftal) and alfalfa (Lucerne) also suffer similar damage by H. armigera. The population dynamics and seed yield losses by the pest on popular genotypes of these forage legumes were studied for 3 consecutive years (2006-07 to 2008-09). Across genotypes, H. armigera build up started in standard meteorological week (SMW) 16, reached a peak value of 11.3 larvae/m(2) in SMW 19, and declined to a low of 0.4 larvae/m(2) in SMW 25. The overall pooled mean larval population was 3.27 +/- 0.034, 2.74 +/- 0.034, 2.56 +/- 0.034, 1.06 +/- 0.034 and 0.33 +/- 0.034/m(2) in berseem varieties BL 1, BL 42, BL 10, lucerne variety LLC 5 and shaftal variety S 69, respectively. The avoidable yield losses were highest in Egyptian clover genotypes BL 10 (72.51 - 74.52%) followed by BL 42 (69.53 - 71.83%). Alfalfa (LLC 5) and Persian clover (S 69) recorded much lower yield losses of 40.46-45.70% and 25.26-31.10%, respectively. Among the three recommended insecticides, endosulfan 35 EC@ 2.5l/ha recorded the highest cost-benefit (C:B) ratios of 1:7.6 to 1:20.9 as compared to 1:4.8 to 1:19.8 and 1:4.0 to 1:17.5 in case of indoxacarb 15 EC@ 500ml/ha and spinosad 48 SC@150 ml/ha, respectively.