Population dynamics and efficacy of biopesticides and entomopathogenic nematodes against Fall Armyworm, Spodoptera frugiperda (J. E. Smith) in Maize
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Date
2021-06
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Department of Entomology, BAU, Sabour
Abstract
Maize is a staple crop in India. The recent invasion of fall armyworm, Spodoptera frugiperda (J. E. Smith) threatens the food security of millions of people. Economic damage in maize is mainly associated with defoliation of the whorl by fall armyworm larvae, although the insect also acts as a ‘cutworm’ by severing the main stem near the crown early in the growing season. It has potential to cause damage up to 100 %. Hence, in light of above facts the present study was undertaken with the following objectives: 1. Population dynamics of S. frugiperda in maize, 2. Comparative efficacy of bio-pesticides against S. frugiperda under laboratory condition, and 3. Bio-efficacy of entomopathogenic nematodes, Steinernema carpocapsae against S. frugiperda under laboratory condition.
During the period of investigation it was observed that the initial average population of fall armyworm in the first week of January was 2.05 at 30 days old crop and reached to peak in the first week of March with a mean population of 22.32 at 89 days old crop, thereafter it declined and low population was found throughout the cropping season of Rabi, 2019-20 while, the activity of fall armyworm started in the last week of July with initial average population of 2.52 at 30 days old crop with maximum population in last week of August at 59 days old crop, then declined gradually and remained associated throughout the cropping season of Kharif, 2020. The correlation studies of fall armyworm and abiotic factors during Rabi, 2019-20 revealed that relative humidity was positively associated whereas rainfall and sunshine hours was negatively associated with the population build-up of fall armyworm. However, remaining parameters did not show significant correlation with fall armyworm population. During Kharif, 2020 with regards to the population of fall armyworm not any significant correlation was found with the weather parameters. Further, different bio-pesticides (mycotoxins) at three different doses and one semi synthetic biopesticide were tested against fall armyworm in vitro, the result indicated that the Emamectin benzoate @ 0.4 g/l caused highest per cent mortality (100 %) within 72 hours after treatment application. While, Metarhizium anisopliae @ 7 ml/l caused 100 per cent mortality after 96 hrs of application. Efficiency of entomopathogenic nematode, Steinernema carpocapsae was evaluated at five inoculums levels i.e., 100, 200, 300, 400 and 500 IJs against S. frugiperda. Result showed that Steinernema carpocapsae could bring 100 per cent mortality of S. frugiperda within 72 hrs, applied at 500 IJs/ petri plate. The results revealed that the mortality of S. frugiperda larvae increased due to the increase in the inoculum level and period of exposure up to certain level.
The present investigation reflects that the mycotoxins of Metarhizium anisopliae can able to generate toxicity to the larval instars and their detoxifying enzymes could be suitable to replace the toxic chemicals available in the pesticide market. The results also demonstrate the possibility of using the entomopathogenic nematode (EPN) as biological control agents for S. frugiperda.
Thus, the fungal bio-pesticide, Metarhizium anisopliae and the entomopathogenic nematode (EPN), Steinernema carpocapsae appeared more effective and can be alternative to chemical pesticide. Hence, these may be incorporated in Integrated Pest Management strategies against S. frugiperda.