BACKGROUND The occurrence of Spodoptera frugiperda (J.E. Smith) in Asia was reported for the first time from Karnataka in 2018. This pest is widely distributed in India, causing significant damage to maize. Management of this recent invasive pest in maize‐growing regions of India relies on chemical control. Resistance is the greatest obstacle to the successful use of chemical insecticides to control this pest. Indiscriminate use of chemical insecticides destroys beneficial natural enemies, therefore effective and sustainable alternative control strategies are needed. In this case, the use of biological control agents is the alternative option to mitigate this pest. Thus, this study aimed to select virulent entomopathogenic nematodes (EPNs) isolates based on the laboratory assay and further to test the efficacy of virulent isolates in the field conditions along with commonly used chemical insecticide emamectin benzoate against S. frugiperda. RESULTS Laboratory results revealed that both Heterorhabditis indica 1 NBAIIH38 and Steinernema carpocapsae NBAIRS59 caused 100% mortality in third‐ and fourth‐instar larvae of S. frugiperda, while these two species caused 85% and 72% mortality in pupae, respectively. When pupae of S. frugiperda were exposed to EPNs, pupae died after metamorphosis to malformed adults. All the nematode species were able to penetrate and reproduce within S. frugiperda larvae, but the reproduction rate for Heterorhabditids was higher than that of Steinernematids. Field trial results showed that H. indica 1 NBAIIH38 significantly reduced the number of larvae and leaf damage scores compared to S. carpocapsae NBAIRS59. Emamectin benzoate was more effective in reducing the larval population compared to EPN species. The cob yield was significantly higher in EPN‐ and emamectin benzoate‐treated plots than in untreated control plots. CONCLUSION Overall, these experiments suggest H. indica 1 NBAIIH38 is a promising biocontrol agent against S. frugiperda in maize production. © 2022 Society of Chemical Industry.
The Oriental armyworm, Mythimna separata Walker (Lepidoptera: Noctuidae) is a major pest of cereal crops, and its outbreaks result in complete crop loss. In this study, we tested the pathogenicity and reproductive potential of indigenous entomopathogenic nematodes (EPNs), Heterorhabditis indica Poinar, Karunakar, & David NBAIIH38, Steinernema abbasi Elawad NBAIISa01, S. carpocapsae Weiser NBAIISc05 and S. siamkayai Stock, Somsook and Reid NBAIRS92 against larval and pupal stages of M. separata under laboratory conditions. Steinernema carpocapsae caused significantly greater mortality in second‐ and fourth‐instar larval stages than other EPNs species. Steinernema carpocapsae caused greatest mortality 100% in larval stages and 75% in pupal stages. Significant differences were observed in the lethal concentration values (LC50 and LC90) of EPNs species against different stages of M. separata. Differences in penetration and multiplication in the fourth‐instar larval stages of M. separata were observed amongst the EPNs species. However, further studies are needed to reveal the field performance of EPN isolates tested to be included in the IPM programme of M. separata.
Summary A new species of entomopathogenic nematode, Steinernema indicum n. sp., was isolated from a coconut palm (Cocos nucifera) field in the district of Udupi, Karnataka, India. The infective juveniles (IJ) of S. indicum n. sp. possess a body length of 1043 (869-1172) μm. The lateral fields are formed by eight equally spaced and developed ridges (nine incisures) in the mid-body region, giving the formula 3, 8, 7, 5. The excretory pore is located posterior to the mid-pharynx region (D% = 63), and the hyaline region occupies ca half of the tail length. The first-generation males are characterised by very short spicules 66 (60-70) μm long. The male spicules are moderately curved with a sharp tip and are golden-brown in colour with the manubrium elongate and with a length to width ratio of 1.92:1. There are 11 pairs of genital papillae plus a single midventral papilla located anterior to the cloacal region. The first-generation male of S. indicum n. sp. is characterised by the presence of a single dorsal postcloacal papilla, a typical diagnostic character that has not been reported from any other steinernematid species. The first-generation male tail has a short mucron present in ca 40% of specimens examined and a second-generation male tail showing a short mucron present in ca 65% of male specimens examined. The first and second-generation females possess a slightly protruding post-anal swelling. The new species is further characterised by sequences of the internal transcribed spacer (ITS) and partial 28S regions (D2-D3) of the ribosomal DNA (rDNA). Phylogenetic analyses confirm that S. indicum n. sp. belongs to the glaseri-group and, based on both ITS and D2D3 genes, showed that S. indicum n. sp. is a member of the karii clade.
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