Effect of belt expert (Flubendiamide + Thiacloprid), Imidacloprid, Thiamethoxam seed treatment and economic impact on fall armyworm (Spodoptera frugiperda) infestation on Maize in Nigeria

Abstract

Fall Armyworm (FAW) Spodoptera frugiperda infestation in Nigeria has reduced the yield of maize by over 40%, especially where control measures are not implemented adequately or effectively. The concealed feeding behavior of the larvae in the leaf whorl makes its control with insecticide difficult, especially for older larvae as a high volume of insecticide will be required to reach the hidden larvae. This can increase the potential of pest exposure to insecticide, selection pressure and consequent development of resistance. One of the new control strategies being developed for this pest is the use of new insecticides of a different mode of action; Belt Expert (Flubendiamide + Thiacloprid) applied at a threshold of 20% (11,000 plant samples/ha) infestation. Flubendiamide + Thiacloprid gave yields similar to conventional insecticides (Emamectin Benzoate and Lambda-cyhalothrin + Chlorantraniliprole) which were better than the untreated. Another approach is the use of seed treatments (Imidacloprid, Thiamethoxam, Apron plus) followed by 2 foliar sprays with Ampligo (Lambda-cyhalothrin + Chlorantraniliprole) at 2, 4, 6 and 8 weeks after planting (WAP). Treatment with imidacloprid or thiamethoxam seed treatment flowed with foliar application of Ampligo at 4WAP significantly had the lowest larval count and highest percentage maize grain yield with a significant yield increase of >15% over the untreated. The use of insecticide with a different mode of action in the targeted pest density and a seed management-based approach may be significant in the management of pest resistance. Future works should focus on integrating some of these approaches in the management of FAW in Nigeria.

Keywords:

• fall armyworm
• Invasive
• Management
• Maize
• Sustainable
• Yield increase

1. Introduction

Maize is an important staple food grown in Nigeria with diverse use as domestic food and a commercial crop on which many agro-based industries such as flour mills, breweries, confectionery and animal feed manufacturers depend for raw materials (Babatunde et al., 2008; Iken & Amusa, 2004). Many Nigerian rural families depend on maize as a source of food and income derived from its cultivation, processing, and marketing (Degrande & Duguma, 2000); thus, maize plays a very important role in national growth and development. It is the fourth most consumed cereal in the country after sorghum, millet, and rice (Cadoni & Angelucci,). It is widely grown across the different agroecological zones of the country, ranging mostly from the rainforest ecology to the savanna zone, especially the Northern Guinea savanna (Olaniyan, 2015). Its production is more concentrated in the savanna than in the forest region because the yield potential is much higher in the savanna simply due to high solar radiation, less incidence of biotic stresses, and natural dryness at the time of harvest (Iken & Amusa, 2004). Its production is mainly in the hands of small farmers, where it is usually intercropped with other crops such as Guinea corn, rice, cowpea, groundnut, and soybeans during the rainy season (Cadoni & Angelucci, ; Iken & Amusa, 2004). In addition, the crop is also grown under irrigation, especially in northern Nigeria (Kamara et al., 2020), therefore its production is all year round in Nigeria. However, maize production is limited by many constraints, including drought stress, low soil fertility, unavailability of improved germplasm, uncertain access to markets, and increased attack by pests and diseases (Kamara, 2017 & Kamara et al., 2020), especially invasive pest. The recent invasion of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in Nigeria is putting maize production at risk.

Fall Armyworm, is a nocturnal polyphagous moth from the subtropical regions of the United States, South America, and the Caribbean region (CABI, 2016; Todd & Poole, 1980). It is now widely established in sub-Saharan Africa predominantly ravages cereals (CABI, 2016; Pogue, 2002; Silva et al., 2015). The pest invaded Africa through West Africa (Nigeria, Sao Tomé, Benin and Togo) in early 2016 (Goergen et al., 2016) and then spread to Central, Eastern and Southern Africa in late 2016 and early 2017 (FAO, 2017), Asia in 2018 (Sharanabasappa et al., 2018) and Australia in 2020 (IPPC, 2020). The growth, development and distribution of the pest are supported by a warm, humid environment in addition to the presence of its preferred host plant (CABI, 2016 &, 2017). Its rapid spread and distribution are predicted to cause serious economic losses of grain crops in many other countries in the near future (FAO, 2017).

Maize is one of the most suitable crops for the FAW (Devi, 2018) where the larval stage of the pest attacks the crop leaf tissue, the whorl, burrowing and destructing growing point resulting in severe defoliation (FAO, 2018) and consequently total crop loss (Cruz & Turpin, 1982). In addition to the attack on crop leaf tissue, it also attacks maize tassels and cobs (Goergen et al., 2016). The larval hidden feeding habit in the plant whorl makes it escape many insecticide applications (Cook et al., 2004), which sometimes gives the impression that the insecticide being used is ineffective and consequently influences the use of a high volume of insecticide.

Since the FAW report in Nigeria, it has become the most predominant destructive pest of maize (Midega et al., 2018) resulting in a reduction in grain yield of up to 40% (Lima et al., 2010) or more (Kamara et al., 2020). The economic loss due to FAW infestation on maize in Africa was estimated to be about US$13 billion (FAO, 2018). In addition to maize, the pest has also been reported to attack other important crops such as sorghum, millet, wheat and some horticultural crops (CABI, 2017; Pogue, 2002; Silva et al., 2015) as well as some grasses growing adjacent to crop fields (Lima et al., 2010). Although no official report of its attack on other crops in Nigeria, however, its feeding damage was observed on crops such as cowpea, groundnut, potato, soybean and cotton in Africa (Goergen et al., 2016) hence, the likelihood of FAW infesting other crops of significant social and economic value in the country in the future.

The threat of FAW and the response of farmers through the indiscriminate use of insecticides in Nigeria (Odeyemi et al., 2020) may increase the cost of production in terms of the amount of insecticide used. Furthermore, the frequent use of insecticides by farmers and excess residues emanating from the indiscriminate use of insecticides contribute to environmental pollution and the killing of beneficial insects, as well as predisposing farmers to the harmful effect of pesticides (health challenge). Resource-poor farmers who have little or no knowledge about pest management are more at increased risk. A survey conducted in Nigeria found that farmers were responding to FAW attacks using an array of insecticides including herbicide (Atrazine), which are being used indiscriminately (Odeyemi et al., 2020). This attitude calls for concern because the indiscriminate use of insecticide exposes the pest to more selection pressure which in turn evokes insecticide resistance. The pest has already been reported to be resistant to organophosphate and pyrethroid insecticides (Zhang et al., 2020), which are among the insecticides being used by some farmers to control FAW in Nigeria (Odeyemi et al., 2020). Indiscriminate use of insecticides leads to the development of resistant and excessive insecticides in the environment, however, judicious use of insecticides including the choice of appropriate method and time of application, insecticides with different modes of action can pave the way for sustainable management of FAW. Belt Expert 480SC® is a new insecticide containing 2 active ingredients (Flubendiamide + Thiacloprid). Flubendiamide belongs to the Diamides class of insecticides and exhibits excellent larvicidal activity through contact and ingestion modes of action against many lepidopterans’ pests (Kodandaram et al., 2010). Thiacloprid is a class of insecticides with a systemic mode of action that is used in crops to control sucking and chewing insects (Kodandaram et al., 2010). Furthermore, Suhail et al. (2000) reported that maize seed treatment with insecticide before planting protects the seeds from soil pests and early season attacks on seedlings up to some period of the plant growth depending on the seed dressing chemicals.

The current research was conducted to evaluate the potential of insecticide with different modes of action as well as seed treatments along with foliar insecticide application based on a threshold of infestation in managing FAW infestation. The general idea was to develop an approach that may set a phase in reducing the indiscriminate use of insecticides, and manage the potential of the insect (FAW) becoming resistant early enough with a resultant maize yield increase.

2. Materials and methods

2.1. Experiment 1

A multi-location trial was conducted in three locations in Northern Nigeria; 1. Samaru Research Farm of the Institute of Agricultural Research (IAR), (11° 11¹ N,07°38¹E), Zaria Kaduna state which is located in the Savannah of northern Guinea. 2. Lere (10° 24,117.795 ‘N, 08° 37¹6.8221” E) Kaduna state, southern Guinea Savannah and Mokwa (09° 21¹43.0571^” N,05°1¹17.79312” E) Niger state Sudan Savannah. The three locations were chosen based on their history of maize production and the prevalence of fall armyworm infestation during the 2018 cropping season.

For each location (Lere, Samaru and Mokwa) an experimental field of 28.5 m x 24.5 m was sprayed with Glyphosate at 4 l/ha after which (2 weeks later) the land was ploughed and divided into plots of 8 rows each measuring 5 m long. Maize seed (SAMMAZ 17), a medium duration variety obtained from (IAR), Ahmadu Bello University (ABU), Zaria was planted at 0.75 m and 0.25 m inter and intra row spacings, respectively, at the rate of three seeds per hole. A week after emergence, the seedlings were thinned to 1 stand/hole. The treatment plots were separated from each other by a 1 m alleyway and 1.5 m between the replicates. Lagon (Aclonifen + Isoxaflutole (Bayer); a selective maize selective herbicide, was sprayed immediately after planting at 600 ml/ha. In addition to the use of herbicide, manual hand weeding using a hoe was applied to manage weeds infestation were necessary. The first dose of fertilizer applied was NPK (15:15:15) as a top dressing at 200 kg/ha 2 weeks after sowing, followed by Urea at 100 kg/ha at 6 weeks after sowing.

There were four treatments in each location as follows: 1. Belt Expert 480SC® (Flubendiamide + Thiacloprid) obtained from Bayer Middle Africa Limited as a test candidate), 2. Ematex (Emamectin benzoate), 3. Ampligo (Lambda-cyhalothrin + chlorantraniliprole) and 4. Untreated plot control sprayed with just water. The Ematex and Ampligo are known to be effective against Lepidopteran pests including FAW thus used as the standard control, comparing their efficacy along with Belt Expert. The treatments were laid out in a Randomized Complete Block Design (RCBD) with four replications. There were three insecticide application; 1^st and 2^nd application for each insecticide and the 3^rd application were made using Decis (Deltamethrin) in all the treatments except the untreated control which was sprayed with water.

The time for the first application of insecticide was determined from the 4 maize leaves (BBCH14) stage, i.e. 2 weeks after planting, based on scouting the 2 central rows of each treatment field before the treatment, then treatments were applied when 10% of the plants showed signs of infestation (leave damage and larval infestation). In this case, Davis and Williams (1992) damage scale 3 was used as a reference for leave damage. The repeated (2^nd) application of insecticide started when 7 leaves unfolded which occurred between 15–20 days after the first application and for the third application was when 9 or more nodes were detectable (between 15-20 after the second application). The insecticides were applied after calibration, using a separate 20 L capacity knapsack sprayer (Jacto) for each to prevent contamination. The insecticides were applied following the manufacturer’s recommendation of 150 ml/ha for Belt Expert; 400 ml/ha for Ampligo; 200 g/ha for Ematex and 100 ml/ha for Decis. The polythene sheet was spread along the site of other adjacent treatments to prevent spray drift.

A 5 m x 28 m plot was divided into four subplots with a 1.5 m alley in between and each subplot represented a treatment (Belt expert, Ampligo, Ematex, or untreated control). The treatments were laid out in a Randomized Complete Block Design (RCBD) with four replications. All the insecticides were applied 2 times following the manufacturer’s recommendation of 150 ml/ha for the Belt Expert; 400 ml/ha for the Ampligo and 200 g/ha for Ematex, from two weeks after planting at each time when a 20% larval threshold was observed until 49 days after planting. Twenty plants were randomly selected from 2 central rows (5 m x 1.5 m) for each treatment (5 m x 6 m) plot, 24 hours after each spray for observation of live larvae. A damage severity scale of 1–9 was used 24 hours after each spray to classify larval damage on the leaf of 20 randomly selected plants from 2 central rows of each treatment; Where 1 = no damage and 9 = more than 60% damage to the leaves (25). When dried and matured, the maize cobs of the two central rows for each insecticide treatment were harvested, threshed, weighted, and used to compare yield.

2.2. Experiment 2

A trial was planted at Samaru Kaduna state in June 2018 and 2019 cropping seasons. The experimental field of 21 m x 90 m was sprayed with glyphosate at the recommended dose of 4 L/ha, after which (2 weeks later) the land was ploughed and divided into plots of 5 rows each measuring 6 m long. Maize seed (SAMMAZ 17) obtained from the Institute for Agricultural Research (IAR), Ahmadu Bello University Zaria was planted at a spacing of 0.75 m and 0.25 m inter and intra row spacings respectively at three seeds per hole. Two weeks after planting, then thinned to one seed/hole. The treatment plots were separated from each other by a 1 m alleyway and 1.5 m for replicates. Pendimethalin (a selective herbicide) was sprayed immediately after planting. Manual hand weeding with a hoe was applied to manage weed infestation. NPK fertilizer was applied as top dressing at 200 kg/ha 2 weeks after sowing, followed by Urea at 100 kg/ha at 6 weeks after sowing.

There were 13 treatments that included 3 seed dressing chemicals Actara 250® (Thiamethoxam), IMITEX 350® (Imidacloprid) and Apron star 42WS® (20% w/w Thiamethoxam+ 20% w/w Metalaxyl-m + 2% w/w Difenoconazole) and 4 timings of foliar sprays with Ampligo® (Lambda-cyhalothrin + chlorantraniliprole) and untreated control.

2.3. Seed dressing

The seed dressing chemicals were applied at the recommended rates; Thiamethoxam (8 g/Kg), Imidacloprid (8 ml/Kg) and Apron star (2.5 g/Kg). Two kilograms of Maize seeds were placed with each chemical separately in a 10 cm x 12 cm polythene bag and a few drops of water were added and then shaken continuously until the seeds were fully coated with the chemical. The seeds were then dried for two hours under shade and planted the same day. The treatments were arranged in a Randomized Complete Block Designed (RCBD) with four replications

2.4. Foliar application of ampligo

Four timings of foliar sprays for each seed treatment with Ampligo (400 ml/ha) was done at the first spray when signs of leaf damage by the larvae were observed in 10% of the plants, and at 4 (28 days), 5 (35 days) and 6 (42 days) weeks after planting. Each of the foliar applications was made twice at 14-day intervals. The untreated plot was used as a control.

Data on the larval count, damage severity and grain yield in each of the experiment were subjected to Analysis of Variance (ANOVA) to compare the treatments for significant differences and where significant difference exists, Student Newman Keuls (SNK) was used to separate differences among the treatment means at 5% level of probability. The value of grain yields was used to calculate the economics of using the different insecticide treatments using a model (Shabozoi et al., 2011). The analysis was done based on the prevailing market price of the crop (US$40.9/100 kg) and all the variables of production including the cost of protection (insecticide and their cost of application) in the 2022 season. The net benefit (NB) and the benefit-cost ratio (BCR) were worked out. Net benefit/ha for each treatment was obtained by subtracting the total cost of crop protection from total income (yield of grain kg/ha x the prevailing selling price per kg). The benefit of each spray treatment over the untreated was obtained by subtracting the total income of the untreated from the net benefit of crop protection. The BCR was obtained by dividing the benefit of each protection by the cost of crop protection for each treatment.

3. Results

Table 1 shows that Belt-Expert had a similar larval count, leaf damage severity, and yields with the two standard insecticide checks (Ematex and Ampligo) that were significantly (p < 0.05) lower than the untreated. The result indicated a yield increase of between 0.7% and 2% for Belt-Expert over the two standard checks and 19% in the untreated. The economic analysis shows that 2 Belt Expert at 10 days intervals had the highest net benefit of US$ 2,113/ha compared to other treatments, which had a net benefit of less than US$ 2,000. The untreated had the least net benefit of US$ 1,252.2. However, when untreated was compared with other treatments, it shows a minimum loss of US$ 701 when none of the insecticides were applied.

Table 1. Larval infestation, yield and economic analysis of maize treated with insecticides in Nigeria

			Grain Yield t/ha
Treatment	Mean live larval count/20 plants	Damage severity	2018	2019	Mean	% Yield increase over untreated	Total cost (US$/ha)	Net benefit (US$/ha)	Benefit-cost ration
Belt Expert*	1.3b	1.7b	3.7a	3.0a	3.4a	19.3	668.2	2,113.6	3.2
Ematex	1.8b	1.6b	3.4a	3.1a	3.2a	17.8	664.1	1,954.1	2.9
Ampligo	0.9b	2.0b	3.5a	3.1a	3.3a	18.6	711.4	1,988.6	2.8
Untreated	6.5a	4.5a	2.3b	2.2b	2.3b	-	629.6	1,252.2	1.9
SE± P-value	0.6 0.01	0.4 0.01	0.9 0.01	0.2 0.01	0.6 0.01	-

*New insecticide; with only two applications for each insecticide, starting from when a 20% FWA infestation was observed; a combined data for three locations.

Table 2 shows the results obtained from the research conducted to study the effect of three seed treatment chemicals together with foliar sprays on FAW infestation. The result indicated that Imidacloprid (8 ml/kg) or Thiamethoxam (8 g/kg) seed was treated followed by 2 foliar applications of Cyper plus (1 L/ha) 4 weeks (28 days) after planting (WAP) and 10 days flow-up spray significantly had the least mean larval count than seed treatments with other periods of foliar application. The result indicated that maize seed treated with imidacloprid or Thiamethoxam flowed with the foliar application of Ampligo in 4WAP had the highest percentage of maize grain yield and an increase in yield of 48% and 49% respectively over the untreated. Furthermore, economic analysis shows that maize seeds dressed with Thiamethoxam and Imidacloprid, followed by 2 foliar applications of Ampligo at 4WAP had the highest net benefit of US$ 2,461.3 and US$ 2,386.6 respectively compared to other treatments which had a net benefit of between US$ 1,317.6—US$ 2,115.9. The untreated had the least net benefit of US$ 1,078.3. There was a minimum loss of US$ 240 where none of any of the treatments was applied.

Table 2. Effect of seed treatment and time of foliar insecticide application on maize grain yield and economic return

Seed treatment	Period of foliar application with Ampligo	Mean live larval count/20 plants	Grain yield (t/ha)	% yield increase over untreated	Total Cost (US$/ha)	Net benefit (US$/ha)	Benefit-cost ration
Thiamethoxam	2WAP	8.2b	3.1b	42.0	729.6	2,115.9	3.0
Imidacloprid	2WAP	6.5b	3.1b	40.0	722.5	1977.5	2.7
Apron star	2WAP	6.8b	2.9b	31.6	727.9	1,644.8	2.3
Thiamethoxam	4WAP	6.4bc	4.1a	49.8	729.6	2,461.3	3.4
Imidacloprid	4WAP	4.1c	3.9a	48.0	722.5	2,386.6	3.3
Apron star	4WAP	6.7b	2.9b	35.7	727.9	1,644.8	2.3
Thiamethoxam	6WAP	7.2b	3.2b	41.4	729.6	2,052.2	2.8
Imidacloprid	6WAP	6.5b	3.0b	31.2	722.5	1,732.0	2.4
Apron star	6WAP	8.9 ba	3.0b	33.9	727.9	1,726.6	2.4
Thiamethoxam	8WAP	8.2 ba	2.9bc	29.6	729.6	1,643.1	2.3
Imidacloprid	8WAP	9.1 ba	2.9bc	30.5	722.5	1,650.2	2.3
Apron star	8WAP	7.3b	2.5c	17.3	727.9	1,317.6	1.8
Untreated Control	-	11.0a	2.1c	-	639.9	1,078.3	1.7
SE± P-value		1.20 0.001	0.181 0.001	-

WAP: week after planting. Each treatment was sprayed twice, with subsequent spray done 10 days after each first spray.

4. Discussion

The feeding and fast insecticide-resistant development behavior of the FAW larvae suggest the need for a new control approach for the effective management of the pest. This study demonstrated that 2 targeted Belt-Expert sprays each at 20% FAW larval infestation and maize seed treatment followed by 2 foliar applications of Ampligo are promising as a management strategy for FAW infestation in maize. There was a reduction in FAW larval infestation with a consequent increase in maize grain yield of between 0.7–2% for Belt-Expert over the 2 standard checks and 19% over untreated. The highest economic benefit was obtained in 2 sprays of Belt Expert compared to other treatments This shows the importance of the Belt Expert in managing FAW infestation. The insecticide contained Flubendiamide and Thiacloprid as their main active ingredients. Flubendiamide belongs to the Diamide class of insecticides that exhibits excellent larvicidal activity through contact and ingestion modes of action against many lepidopteran pests (Kodandaram et al., 2010). Thiacloprid is a class of insecticide with a systemic mode of action used in crops to control sucking and chewing insects (Kodandaram et al., 2010).

The importance of using insecticides of different modes of action in the management of FAW has been emphasised by Deshmukh et al. (2020). This is simply because the pest is developing resistance to insecticides mainly organophosphates and pyrethroid insecticides (Zhang et al., 2020). In Nigeria, most of the insecticides being used for managing FAW belong to these classes of insecticides, which may be the reason some farmers were reporting cases of the ineffectiveness of some insecticides (Odeyemi et al., 2020). Thus, this necessitates the need for proactive measures, particularly the use of insecticide in a different mode of action which may delay the insect from becoming resistant early enough. The use of insecticides with multiple modes of action along with other control strategies has been reported to be an effective strategy for insecticide-resistant management (McCaffery & Nauen, 2006; Zhu et al., 2016).

Our second study demonstrated that the use of Imidacloprid (8 ml/kg) or Thiamethoxam (8 g/kg) as seed treatment followed by 2 foliar applications of Ampligo (1 L/ha) at 4 weeks (28 days) and 38 days after planting (DAP) has the potential to keep FAW infestation low with consequent improvement in maize grain yield. This approach had the highest percentage increase in maize yield (48% and 49% respectively) compared to the untreated. Imidacloprid (Almand, 1995) and Thiamethoxam (Prasanna et al., 2004) are reported to provide good plant protection against some root-feeding and early-season insect pests. Wheat seed treated with Imidacloprid prior to planting was found to have a low infestation with a consequent increase in wheat yield (Milosavljevi et al., 2019). Apron star 42WS® (20% w/w Thiamethoxam+ 20% w/w Metalaxyl-m + 2% w/w Difenoconazole) has been one of the common seed treatment chemicals used in Nigeria. Furthermore, the economic analysis shows that maize seeds dressed with Thiamethoxam and Imidacloprid, followed by 2 foliar applications of Ampligo at 28 and 38 DAP, had the highest net benefit compared to other treatments. The untreated had the least net benefit. However, when untreated was compared with other treatments, it shows a minimum loss of US$ 240 where none of any of the treatments was applied. It can be suggested from this work that seed treatment and the foliar spray strategy have the potential to be a good management strategy for FAW in Nigeria.

5. Conclusion

This study reveals that two targeted sprays of the maize field with Belt Expert, each at a 20% infestation threshold, as well as seed treatment followed by two foliar insecticide sprays with Ampligo at 10-day intervals, have the potential for effective management of FAW infestation and consequent improvement in maize grain yield. The approach may be best practice when integrated with other control methods in the integrated pest management (IPM) approach. Therefore, future research should explore the compatibility of our strategy with other control methods in an IPM approach. More research is required to determine the potential of the approach to reduce pest resistance to insecticides.

Acknowledgements

The authors wish to acknowledge the financial support from the Institute for Agricultural Research (IAR), Samaru, Zaria, Nigeria, and Bayer Middle Africa LTD.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors received no direct funding for this research.