Crop-Livestock Integration: Attack of Spodoptera frugiperda (Lepidoptera: Noctuidae) on transgenic maize and Bachiaria brizantha (Poaceae)¹

ABSTRACT

The Crop-Livestock Integration system has sustainable potential. But pests such as the defoliating caterpillar Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) can reduce the productivity of this system. The objective was to report transgenic maize and Brachiaria brizantha (A. Rich.) (Poaceae) plants attacked by S. frugiperda in the Crop-Livestock Integration system. Feroz VIP3 ^® transgenic maize (SYN8A98 TLTG Viptera) and B. brizantha MG-5 Xaraés plants attacked by S. frugiperda were evaluated 20 days after planting, weekly and for 28 days. The transgenic maize plants were less attacked by S. frugiperda than those of B. brizantha. The negative impact of this pest on B. brizantha suggests the planning and adopting strategies for its control, such as the use of traps, resistant cultivars, and biological or chemical products, minimizing losses in animal production and, consequently, in human food.

Keywords
Bacillus thuringiensis; consortium; foragers; grazing; pest insect

INTRODUCTION

The Crop-Livestock Integration (CLI) production system encourages diversification, rotation and planned to intercrop agricultural and livestock activities (Kunrath et al., 2015). Rational soil management in this system improves carbon accumulation and conserves fertility by forming bioactive humic substances responsible for increasing plant performance (Baldotto et al., 2017; Bansal et al., 2022). In addition, it is favorable for the establishment of crops, especially in degraded areas (Assis et al., 2019; Carvalho et al., 2020).

Livestock in Brazil is heavily dependent on pastures occupied, in the majority, by Brachiaria spp. Trinius (synonym Urochloa P. Beauv.) (Poaceae) for the production of animal protein (meat and milk), being identified as responsible for environmental impacts, such as the production of greenhouse gases related to climate change (Gléria et al., 2017; Lima et al., 2022). The intercropping of forages with annual crops, such as maize and sorghum, is an efficient and economically viable technique for forming, recovering, and renewing pastures in the CLI (Geremia et al., 2018). This consortium can occur with the simultaneous or sequential sowing of species in which, after harvesting the annual crop, the pasture formed is intended for animal feed (Roese et al., 2018; Tsufac et al., 2021).

The maize (Zea mays Linnaeus) (Poaceae) is an important cereal originating in the Americas and cultivated on a large scale in the world, with Brazil being the third largest producer with an area of 20 million hectares and production of 87 million tons (Leite et al., 2021; CONAB, 2021). This crop is susceptible to climatic fluctuations and the attack of diseases and pests, causing high economic impact (Dos Santos et al., 2020). Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), the main pest of maize in Brazil, feeds on a wide variety of plants, such as cotton, rice, forages, and soybeans, among others (Scoton et al., 2020). The control of S. frugiperda has been carried out mainly with the excessive use of insecticides, which select resistant individuals of this insect in the field (Omoto et al., 2016). The cultivation of transgenic maize expressing insecticidal proteins (Cry and Vip) derived from the bacterium Bacillus thuringiensis (Bt) Berliner is efficient in controlling S. frugiperda and is an alternative to the excessive use of chemicals (Castro et al., 2019; Zhao et al., 2020).

The population dynamics of pests have been studied for monocultures, and these studies are scarce for the CLI system. The CLI with transgenic maize and B. brizantha can be attacked by S. frugiperda, and the survival and development of this pest in forage can increase the pressure of insects on transgenic maize. In this context, the objective was to report transgenic maize and B. brizantha plants attacked by S. frugiperda in the Crop-Livestock Integration system.

MATERIAL AND METHODS

The experiment was carried out at Rodeio Gaúcho Farm (22°47’42.1” S and 42°26’25.8” W, 42 m.a.l.s.), coastal lowland of Araruama, state of Rio de Janeiro, Brazil, between February and May 2022, second crop (cultivation after the main harvest) of maize. According to the Köppen-Geiger classification, the region’s climate is of the Aw type, with average annual temperature and precipitation of 24°C and 1103 mm, respectively (Climate-Data, 2022).

The CLI system was established in an area with 9.6 ha, after plowing and harrowing the soil, without liming and with fertilization of 350 kg/ha of formulated (08-28-16) for planting.

Feroz VIP3^® transgenic maize (SYN8A98 TLTG Viptera) and B. brizantha Série Gold^® MG-5 Xaraés were cultivated in intercropping, in this study, for transformation into silage and subsequent cattle grazing, without the application of insecticides. Maize planting was carried out with a spacing of 0.2 m between plants and 0.65 m between rows, with five plants/m linear and a density of 76,924 plants/ha. The planting of B. brizantha was carried out with 13 kg/ha of seeds by broadcast.

The total area was divided into three sub-areas (3.2 ha), each considered an experimental repetition (Figure 1). Ten random points (2.16 m²) were marked with wooden stakes (1.5 m) and identification tags in each sub-area and, in each of these, 40 plants (20 of maize and 20 of B. brizantha) were sampled for counting plants damaged by S. frugiperda. The evaluations started 20 days after planting, when the plants reached 100% germination, with five evaluations, one per week, over 28 days.

Figure 1
Delimitation of the experimental area for the intercropped cultivation of Feroz VIP3^® transgenic maize and Brachiaria brizantha cv. Xaraés in the Crop-Livestock Integration (CLI) system.

The design was completely randomized with two treatments (maize and B. brizantha) and three replications (subareas), making a sampling effort of 6,000 evaluated plants. The behavior of the curves of attacked plants in the subareas was similar, so the data were grouped for the total area and analyzed to compare the treatments. The data did not meet the assumptions of the ANOVA, and means were compared using the Wilcoxon nonparametric test (P < 0.05). Analyses were performed using RStudio software (RStudio Team, 2022).

RESULTS AND DISCUSSION

The transgenic maize plants were less attacked by S. frugiperda than those of B. brizantha during the evaluated period (Figure 2). This proves the efficiency of transgenics (VIP protein) in controlling this pest. However, injuries such as leaf scraping, caused by S. frugiperda caterpillars of early stages, are expected, as they must ingest insecticidal proteins for their control (Zhao et al., 2020). The S. frugiperda attacks occurred with the presence of only one caterpillar per plant. This is because S. frugiperda has a high degree of cannibalism, allowing the development of only one individual per plant (Scoton et al., 2020). Obtaining clones or forage cultivars resistant to S. frugiperda is important to avoid reducing the productivity of green forage or straw mass caused by this insect (Harrison et al., 2019). These strategies prevent the multiplication of potential pests of forages and annual crops intercropped in the CLI system.

Figure 2
Number (mean ± standard deviation) of Feroz VIP3^® transgenic maize plants and Brachiaria brizantha cv. Xaraés attacked by Spodoptera frugiperda (Lepidoptera: Noctuidae) per intercropped area in the Crop-Livestock Integration (CLI) system.

The number of B. brizantha plants damaged by S. frugiperda stabilized in the second evaluation (Figure 2). This may have occurred due to the increased population of natural enemies of S. frugiperda in the area. Planting forages intercropped with maize increased soil fertility and provided a diverse environment for developing S. frugiperda parasitoids and predators (Harrison et al., 2019; Bansal et al., 2022). Natural enemies of S. frugiperda can recognize herbivory-induced volatiles from intercropped maize and bean plants, consequently resulting in the control of this insect (Udayakumar et al., 2021). Thus, it is suggested that herbivory-induced volatiles from transgenic maize and B. brizantha plants attracted natural enemies of S. frugiperda and stabilized its attack on these crops.

The attack of S. frugiperda on B. brizantha in the CLI system can be explained by the forage being considered an alternative for the pest to maintain and multiply in the area, possibly increasing its attack in this cropping system. Different species of the genus Brachiaria spp. were good hosts for S. frugiperda, allowing the complete development of this insect (Auad et al., 2016). Thus, selecting plants that minimize the biotic potential of this insect pest is one of the challenges in intercropped plantations in the CLI. The minor attack of transgenic maize plants by S. frugiperda occurred due to the Viptera technology (expression of the Vip3Aa20 protein), making these plants more resistant to the attack of this lepidopteran. Four Vip families with more than 100 toxins are known, with Vip3Aa being the only one present in commercialized transgenic crops and with no reports of resistance in the field (Tabashnik & Carrière, 2017). However, populations of S. frugiperda were resistant to Cry1Ab and Cry1F toxins in transgenic maize areas (Monnerat et al., 2015). The Vip3Aa protein can be associated with Cry in pyramidal plants (Figueiredo et al., 2019), delaying the possible development of lepidopteran resistance to transgenic crops.

There was no change in the number of transgenic maize and B. brizantha plants damaged by S. frugiperda in the fifth evaluation (Figure 2). The expression of Vip insecticidal proteins effectively controls this pest in maize, even when its individuals are in more advanced stages of development (Tabashnik & Carrière, 2020). Thus, studies with proteins with higher insecticidal capacity are important for managing resistant insects (MRI).

The number of B. brizantha plants damaged by S. frugiperda was higher than that of transgenic maize plants in the total cultivated area (Figure 3). The ample supply of host plants throughout the year, either through crop succession or through the use of susceptible cultivars, contributes to the occurrence of S. frugiperda (Omoto et al., 2016). Furthermore, in intercropped plantations, S. frugiperda can develop in one host species causing damage to the other, as reported for this insect in plants of Pennisetum purpureum Shum (Poaceae) (cvs. Ouma II and South Africa), B. brizantha (cvs. Xaraés, Piatã and Mulato II) and Melinis minutiflora P. Beauv. (Poaceae) cultivated in intercropping with maize (Cheruiyot et al., 2021). Brachiaria brizantha, in the present study, allowed the survival and development of S. frugiperda, without significant damage to the transgenic maize, with consequent loss of green mass of this forage due to the high number of attacked plants. High population densities of caterpillars in B. brizantha can cause more significant pest pressure on transgenic maize plants and generate a possible reduction in the efficiency of its control and, consequently, economic losses.

Figure 3
Number (mean ± standard deviation) of Feroz VIP3^® transgenic maize plants and Brachiaria brizantha cv. Xaraés attacked by Spodoptera frugiperda (Lepidoptera: Noctuidae) in the total area intercropped in the Crop-Livestock Integration (CLI) system. Means followed by different letters in the column differ by the Wilcoxon test (P < 0.05).

On the other hand, if the pest is controlled in the pasture, keeping populations below the economic damage level (EDL), the CLI system may be recommended to help manage insect resistance to Bt technology. In this sense, the pasture can develop susceptible adults of S. frugiperda, which will mate with resistant individuals and develop new individuals susceptible to insecticidal proteins, as occurs when adopting refuge areas. Therefore, studies involving the population dynamics of S. frugiperda are important to assess the impact of this pest on agroecosystems.

CONCLUSIONS

The infestation of pests in CLI systems with transgenic maize and B. brizantha demands attention, as these pests can migrate from one plant to another.

The S. frugiperda caterpillars developed on B. brizantha plants and did not cause severe damage to the transgenic maize (VIP protein). However, its negative impact on B. brizantha plants suggests the planning and adoption strategies for its control, such as the use of traps, resistant cultivars, and biological or chemical products, minimizing losses in animal production and, consequently, in human food.

ACKNOWLEDGEMENTS, FINANCIAL SUPPORT AND FULL DISCLOSURE

The authors acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for the grants.

The authors declare that there is no conflict of interest.

• 1
  This work is part of the doctor’s thesis of the first author and it was funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).

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Publication Dates

• Publication in this collection
  25 Aug 2023
• Date of issue
  Jul-Aug 2023

History

• Received
  19 Sept 2022
• Accepted
  25 Jan 2023