Evaluation of biopesticides against the fall armyworm, Spodoptera frugiperda in maize

Introduction

The fall armyworm (FAW), scientifically known as Spodoptera frugiperda (J. E. Smith), is an invasive insect pest that poses a serious threat to global food security, particularly for maize. Originally from neotropical areas of America, the pest migrated to West Africa in early 2016 and has since spread to numerous countries in sub-Saharan Africa. It has further invaded various countries in the western world (Prasanna et al., 2021; CABI, 2022) [11,4] . In India, Karnataka experienced the first outbreak of FAW in 2018, leading to significant economic yield losses in maize, with subsequent spread to major maize-growing areas within a year (Sharanabasappa et [12,13,15] . This highly polyphagous insect pest attacks more than 350 host plants and can complete up to 12 generations in a year in tropical climates (Busato et al., 2005) [3] . The larvae feed on various parts of the plant, causing substantial yield losses. The impact of fall armyworm damage on maize yield has been reported to be about 50-80%, resulting in the loss of millions of dollars (Adhikari et al., 2020) [1] . In Africa, without effective FAW management options, the pest causes significant maize yield losses ranging from 8.3 to 20.6 million tonnes per year, resulting in significant economic losses of $2.5-6.2 million (Mendesil et al., 2023) [9] . In 2017, maize production in India declined by 3.2%, with a production of 27.8 million tonnes due to infestation by insect pests, including the fall armyworm (Manupriya, 2019) [8] . The preliminary studies on yield losses due to FAW are attributed to 33-36% in Indian conditions, (Jagdish et al., 2019; Aruna et al., 2019) [7,2] . Presently, FAW is established in over 42 countries, with an estimated annual impact of $13 billion (Stokstad, 2017) [14] . In Indian conditions, the FAW control is primarily focused on synthetic insecticides which evolved as effective control options. According to the Arthropods Pesticide Resistance Database, there are 42 active ingredients and 182 resistance cases were reported for FAW worldwide (Gutiérrez-Moreno et al., 2019). The overuse and misuse of these synthetic insecticides result in rapid resistance development and control failure.

Thus, utilization of biocontrol agents like as mycopesticides have been seen as an alternative to these hazardous chemical insecticides to effectively manage FAW. This strategy lessens the detrimental effects of chemical pesticides on natural enemies while simultaneously helping to mitigate the problem of insecticide resistance in FAW population. The biopesticides like entomopathogenic fungi are reported to be controlling the FAW population up to 45% in natural conditions of native regions (Guo et al., 2020). In invading countries, the search for native biocontrol agents and utilization of native biocontrol agents provides valuable control options. In view of above context, we framed an experiment to evaluate the native entomopathogenic fungi strains against FAW in field conditions.

Material and Methods

Experimental design

The study was conducted during the winter season (November 2023 -February 2024) at Research farm (21° 14' 55.8312'' N latitude and 81° 38' 24.324'' E longitude), ICAR -National Institute of Biotic Stress Management, Raipur, Chhattisgarh, India. The maize hybrid JKMH -4222 was sown at a spacing of 60×20 cm in a 5 m row length with a plot size of 60 m 2 for each module. The experiments were laid out in randomized block design with three replications. Five different treatments were evaluated and compared the effectiveness along with a control treatment. Recommended package and practices were followed to raise the maize crop except for pest control treatments and a good crop stand was maintained. The EPF (Entomopathogenic Fungi) strains were native to the Chhattisgarh region, India. A total of five different bio-pesticide (Table No. 1) treatments along with untreated check were replicated four times and two rounds of treatment application were taken in the crop duration with sufficient pre-treatment infestation levels, initially at the knee height stage and the second application 15 days after the initial application. Spraying was carried out during calm and warm evenings using a high-volume knapsack sprayer equipped with a hollow cone nozzle. Application rates were set at 400 L per hectare for the first spray and 500 L per hectare for the second. During the first spray, insecticides were distributed on both leaves and whorls, while the second application targeted only the whorls by adjusting the hollow cone nozzle.

Data collection

Visual assessments of live larvae and damaged leaves (%) were recorded from 10 plants per treatment plot excluding border rows, one day before treatment and at 1, 3, 5, 7, 10, and 14 days after the application of treatments. The final observation data of initial spraying was considered as pretreatment observation for the second round of application. Cob damage (%) was taken once at 90 days of crop growth as the number of damaged cobs to the total number of cobs in each treatment plot. Marketable grain yield was measured for each treatment and expressed in kilograms per hectare.

Statistical analysis

All the observations recorded were subjected to appropriate statistical transformations with subsequent ANOVA analysis. Tukey's test was employed for the mean separation with a significance level set at P ≤ 0.01. IBM SPSS 2.0 statistical software is used for data analysis. Results

Population reduction

All the treatments evaluated in controlling the larval population of FAW showed a significant superiority over the untreated check. The larval population of FAW recorded after a day of treatment application resulted in no significant difference among the treatments in continuation to pretreatment observations with 5.25 to 3. was mediocre and on par with each other. L. lecanii (4.92) performance was proved to be worse among all the treatments and it is on par with the untreated check plot

Percent leaf damage

The leaf damage of maize crop due to FAW was uniform on all the treatment plots before the application of respective bio-pesticide treatments ranging from 40.88% to 33.40%. The observations taken after applying treatments after a day (F = 2.27; df = 5, 15; P = 0.09) and 3 (F = 0.87; df = 5, 15; P = 0.52) show no significant difference among the treatments.

The effect of bio-pesticides on the cob damage and yield of maize

The bio-pesticide treatments evaluated significantly reduced the cob damage when compared to the control plot (F = 55.25; df = 5, 15; p<0.0001). The extent of cob damage ranged from 21.67% for the application of B.

Discussion

The field trial aimed to assess the efficacy of various native bio-pesticides against the fall armyworm in maize. The results of the trial demonstrated that all tested bio-pesticide formulations outperformed the control plot in terms of reducing fall armyworm larval populations and minimizing maize damage. The field trial identified B.t var kurstaki 1% WG as the most effective treatment against fall armyworm in terms of reducing larval populations and minimizing leaf damage in maize. M. anisopliae 2% also demonstrated notable efficacy as a native EPF formulation newly evaluated against fall armyworm. Montecalvo et al., 2021 [10] also tested M. anisopliae against FAW reporting effective control in early stage larvae. Azadirachtin 1500 ppm and B. bassiana 1.15% showed moderate efficacy, while L. lecanii 1.15% exhibited the least effectiveness among all bio-pesticides evaluated. In Indian conditions studies related to the evaluation of native entomopathogenic fungi are very limited however, EPF like M. anisopliae, B. bassiana and another bio-pesticide B.t var kurstaki used for controlling the Spodoptera spp are tested against FAW, reported to cause mortality in early instars (Dhobi et al., 2020) [5] . The virulence of most of the EPF were analysed in native and African countries where the efficacy was quite attractive (Idrees et al., 2022) [6] . India, with its diverse ecological conditions, offers great potential for the availability of native biocontrol strains. Similar to the previously evaluated biocontrol agents, there is a need to assess different native strains in both laboratory and field conditions, especially in countries that are invaded by FAW, such as India. This presents ample opportunities for further commercialization.

Conclusion

Overall, the present field trial to evaluate different biopesticides in controlling FAW in maize concluded the commercial formulation B.t. var kurstaki was the most effective. Among the three native EPF strains evaluated, the M. anisopliae was superior to the remaining. Azadirachtin was effective in controlling the early stages of larvae. L. lecanii 1.15% treatment was poor performer in all the conditions.

References

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