Investigation of strains, resistance level and microbial association of Spodoptera frugiperda (Smith)
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Date
2022
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Department of Entomology, BAU, Sabour
Abstract
The present experiment was conducted in the laboratory Department of Entomology, Bihar Agricultural University, Sabour, Bhagalpur during the year from 2020 to 2022. The present investigation was aimed with the following objectives namely, (i) to find out the prevalence of strain of Spodoptera frugiperda present in Eastern India, (ii) to study the degree of resistance acquired by Spodoptera frugiperda against selected insecticides, (iii) to find out the association of microbiomes with Spodoptera frugiperda and (iv) detection of larval parasitoid of Spodoptera frugiperda. The fall armyworm (FAW) larvae had identical morphological characteristics and were identified as S. frugiperda.
The present study successfully amplified S. frugiperda strains by mtCOI-5 in 18 locations in the eastern part of India (Bihar, West Bengal, Jharkhand and Orissa) and found considerable 12 nucleotide position variations when compared with ‘rice strain’ i.e. (R Strain). Similarly, variations were also observed in nucleotide positions when compared with the "corn strain," i.e. (C strain). Thus, phylogenetic analysis of the 18 fall armyworm samples revealed that the Rstrain predominated over the C-strain in the eastern part of India, with the majority of samples, i.e., twelve samples, showing a closer resemblance to the Rstrain and six samples showing a closer resemblance to the C-strain. In addition to that, the resistance levels of fall armyworm were recorded against different chemistries of newer insecticides with different modes of action. The results revealed that among the different districts of Bihar, the Munger population showed the highest resistance ratio (RR50) to sodium channel modulator groups, namely deltamethrin and lambda cyhalothrin, with 9.33fold and 7.67-fold, respectively. As far as the RR50 level of different insecticides is concerned, among the different insecticides, deltamethrin and lambda cyhalothrin showed maximum resistance, followed by chlorantraniliprole and flubendiamide, while emamectin benzoate, spinosad and spinetoram showed highly toxic, i.e., least resistance, against fall armyworm samples collected from different agro-climatic zones of Bihar. On the other hand, the experimental result revealed the composition of bacterial communities present in the larval gut of S. frugiperda and grouped them into each taxonomic category from phyla to species level. Among them, under the phyla Firmicutes and Proteobacteria, the genera Enterococcus and Klebsiella showed more dominance over other groups of bacteria associated with the different location samples of S. frugiperda. Species-level analyses revealed a total of 33 species of bacteria associated with the gut of S. frugiperda, which were collected from various locations in Bihar, West Bengal, and Jharkhand. Among the 33 species collected from various locations, Enterococcus group species are the most abundant, followed by Klebsiella sp. and Enterobacter sp., with a minor proportion of Raoultella, Citrobacter, Leclercia, and Pantoea genus were also present. As we know, biological control is the most promising and ecofriendly pest management approach in IPM, therefore, an experiment was designed to identify the larval parasitoid of S. frugiperda. The present findings revealed that lab-collected braconid parasitoid was successfully preferred for paralysed, oviposition on the metathoracic sternum of fall armyworm. Furthermore, the mean number of eggs, cocoons, and total braconid wasps emerging were also observed from S. frugiperda larvae. The different morphometric parameters like antennae, total length (mm), length of scape (mm), and width of scape (mm), although measured from single male and female individuals, showed similar trends as previously reported, i.e., the values were numerically higher in males than in females. The habitus photo of the braconid larval parasitoid, as well as the male genitalia, clearly showed its resemblance to the species Bracon (= Habrobracon) hebetor. The molecular characterization also provides strong evidence for the presence of a larval parasitoid, i.e. Bracon hebetor.