Evaluation of Locally Available Botanicals for the Management of Maize Weevil (Sitophilus zeamais Motsch.) in Room Storage Condition
From April to July 2019, an experiment was conducted in Khumaltar, Lalitpur (27°39.312′N, 85° 19.586′E, and 1322 m above sea level) to assess the effectiveness of plant materials on maize weevil (Sitophilus zeamais Motsch.) control under laboratory conditions (maintained room temperature of 28.5 ± 2°C, and relative humidity of 72 ± 5%) treatments were Acorus calamus (rhizome powder) @ 5 g·kg−1, Melia azadirach (rhizome powder) seed) @ 5 g·kg−1, Curcuma domestica (rhizome powder) @ 5 g·kg−1, mustard oil @ 2 mL·kg−1, Gingiber officinalis (rhizome powder) @ 5 g·kg−1, rice husk ash @ 5 g·kg−1, and an untreated control. These treatments were evaluated in a completely randomized design (CRD) with three replications. At four months, the grains treated with Acorus calamus had the least weight loss (6.66%), and grain damage (1.23%). Grain damage (18%), and weight loss (62.33%) were the highest in the control treatment. Similarly, grains treated with Acorus calamus had the fewest number of exit holes (3.10 per 100 g of maize seed), while the control treatment had the largest number of exit holes (45.10 per 100 g of maize seed). There was a significantly higher number of weevils in the control treatment (55.80 per 250 g maize grains), but only a few numbers of weevils in the Acorus calamus-treated grains (2.50 per 250 g maize grains). In contrast with other plant materials treated grains, the maize weevil showed a reduced preference for Acorus calamus- treated grains with low weight loss, and grain damage. These findings can be used to promote locally accessible botanicals for maize weevil control in Nepal.
In Nepal, maize is the second most important cereal crop after rice in terms of area (957,650 ha), and productivity (2.96 Mt·ha−1) . Both in the field and the storehouse, this crop is vulnerable to a wide variety of insect pests. A few insects such as Sitophilus zeamais (Motsch.), and Sitophilus oryzae (L.) have been found infesting maize. Rhizopertha dominica (Fabricius), Tribolium castaneum (Herbest), Corcyra cephalonica (Stainton), and Sitotroga cerealella (Oliver) are also reported to attack maize . The maize weevil (Sitophilus zeamais Motsch.) is the most common pest of maize in Nepal . This is a coleopteron insect that feeds on the kernel starch of harvested corn, causing quality, and weight loss . Sitophilus zeamais is believed to cause losses of 20–80% in tropical countries , but losses of 18–40% have been reported in the Chitwan region of Nepal .
Effective and environmentally safe insect control techniques are still lacking in Nepal in storehouses. Synthetic pesticides can be used to control insect pests in storage, but their repeated application leads to residues, detrimental effects on nontarget organisms, and health, and environmental issues . Pest control with pesticides is usually costly for small-scale farmers and a time-consuming process . Given the negative consequences of synthetic pesticides, plant insecticides, which are more biodegradable, less dangerous to humans, and safe for the environment, appear to be a feasible option for controlling weevils . Nepal is home to a wide variety of plant species that contribute to the biodiversity of the country. This plant material can protect stored grain from pests . In fact, fifty plant species can be used to control insect pests on crops, and grains in Nepal . For example, Acorus calamus, Azadirachta indica oil, Melia azadirach seed powder, Zanthoxylum armatum, and Artitimesia vulgaris are some of the remedies that can help reduce corn aphids . These plant compounds have both lethal, and repellent properties but are not toxic to mammals . The aim of this study was to evaluate the efficacy of various botanicals for protecting maize from corn weevil damage in warehouses.
2. Materials and Methods
2.1. Experimental Site and Lab Condition
The study was carried out in the laboratory of the National Entomology Research Centre in Khumaltar, Lalitpur, Nepal. It is located at an altitude of 1322 meters above sea level, at 27°39.312′ north latitude, and 85°19.586′ east longitude. The temperature, and humidity of the study room were maintained using a heater, and recorded daily with the help of a digital thermo hygrometer at 6:00 AM, 12:00 PM, and 6:00 PM during the experimental period. The average temperature, and relative humidity at the warehouse were 28.5 ± 2°C and 72 ± 5%, respectively, during the study period.
2.2. Selection of Plant Materials
Fresh seeds of Melia azadirach, rhizome of Curcuma domestica, Zingiber officinalis, and Acorus calamus were collected from Chitwan, Kavrepalanchowk, and Lalitpur, Nepal, and kept for two months in the shade for drying, and crushed into powder by hand with a mortar, and pestle. The prepared powder remained safe for use in research trials. Fresh mustard oil was collected from oil mills. The mustard oil was stored in a refrigerator held at 4°C until it was used in the experiment. Ash was made by burning rice husks and collecting them in polyethylene bags after being sifted. The maize variety Manakamana-3 was collected from farmers’ fields of Bhakundebesi, Kavrepalanchowk, and used for the experiment. The grain of this maize variety was harvested after five months of planting. At the time of harvesting, the approximate value of the grain moisture content was 15%, and the ambient temperature was 20°C. The grain moisture level was measured by a Willy Dividable Moisture Meter. The grain collected from different farmers’ fields was cleaned, and dried in the sun. The moisture level was maintained at 14%. The grain was stored under a semi-airtight condition in SuperGrain IV-R™ bags (74 cm wide and 64 cm long) of 25 kg holding capacity (supplied by GrainPro Inc.), and open-weave polypropylene bags of the same capacity. The open ends of the SuperGrain IV-R™ bags were cut to fit the height dimension of these polypropylene outer bags. The SuperGrain IV-R™ bags were kept without tightening their open ends (without proper sealing) in order to keep them in semi-airtight condition. The airtightness of the bag can be affected by improper sealing of the end of the bag, and perforations in the plastic cover.
Grain yield (kg·ha−1) at 14% moisture content was calculated using fresh ear weight.
where F.W. = fresh weight of ear in kg per plot at harvest, HMP = grain moisture percentage at harvest, DMP = desired moisture percentage, i.e., 14%; NPA = net harvest plot area, m2, and S = shelling coefficient, i.e., 0.8.
This plot yield (kg·ha−1) was then expanded to grain yield (t·ha−1).
2.3. Experimental Design and Treatment Details
The experiment was carried out from April 1 to July 30, 2019, at the laboratory of the National Entomology Research Centre, Khumaltar, Nepal. Six kg of corn seeds var. Manakamana-3 were used for each treatment, and were kept under a semiairtight condition in SuperGrain IV-R™ bag. An untreated control, and six different botanical treatments including Acorus calamus (rhizome powder) @ 5 g·kg−1, Melia azadirach (seed powder) @ 5 g·kg−1, Curcuma domestica (rhizome powder) @ 5 g·kg−1, mustard oil @ 2 mL·kg−1, Gingiber officinalis (rhizome powder) @ 5 g·kg−1, and rice husk ash @ 5 g·kg−1 comprised the study. The experiment was organized in a completely randomized design (CRD) with three replications (two kg each), and twenty-one experimental units.
2.4. Data Collection and Observations
Data was collected before, and at specific intervals i.e., 60 days, 90 days, and 120 days after setting up the experiment. Using a sampler (Double-tube sampling spear), a 250 g random sample of maize was taken from each experimental unit, and analyzed. The grain damage percentage was calculated with the following formula 
For estimating adult emergence number of live, and dead insects that emerged from randomly taken 100-gram seed samples of each experimental unit were counted.
Weight loss due to insects is calculated by subtracting from the dry weight of grain before the insect feeding to the dry weight of grain after feeding the insect.
2.5. Statistical Analysis
Using GenStat version 18, all data were analyzed using a one-way ANOVA. The Duncan multiple range test (DMRT) was used to compare means which were separated by the least significance difference (LSD) at .
3. Results and Discussion
For the management of maize weevil in storehouses, laboratory tests were conducted to identify ideal botanicals that proved to be superior to synthetic chemicals. The findings were analyzed and discussed, and evidence from previous studies was used to support them.
3.1. Weevil Population
Maize seeds treated with Acorus calamus (rhizome powder) and Melia azadirach (seed powder) had a significantly better effect on the weevil population control compared to other treatments (). The lowest number of weevils was found in seeds treated with Acorus calamus (2.5), followed by seeds treated with Melia azadirach (6.21), mustard oil (19.50), and rice husk ash (28.10), while the highest was found (55.80) in the control (Table 1) at 120 days after treatment.
Paneru et al.  reported that the concentrations of B-asarone in calamus rhizome powder were 6.4%, and 4.7% (mature parts of rhizomes harvested in the highlands, and lowlands, respectively), 3%, 6%, and 4.0. v/v (ripe part of rhizomes harvested in high, and low altitudes, respectively) (young part of rhizomes harvested in high and low altitudes, respectively). By preventing the removal of the exoskeleton during larval development, active phytochemicals such as alkaloids have been reported to inhibit growth, and limit larval survival . Other compounds such as isoflavonoids, flavonoids, and terpenoids have been observed to inhibit insect reproduction, and population growth [19, 20].
3.2. Number of Exit Holes per100 Gram of Maize
The effect of different botanical treatments also had a significant effect () on the number of exit holes made by the weevil. At the end of the experiment, exit holes opened by the weevil were the highest in the control (45.10), and lowest in the seeds treated with Acorus calamus (3.10) (Table 2). The result of a small number of adult emergence studies clearly demonstrated the superior performance of Acorus calamus rhizome powder at 5 g·kg−1 seeds to preserve maize seeds for four months. A few eggs laid on Acorus calamus rhizome powder @ 5 g·kg−1 seeds did not complete their development resulting in a reduced number of adult emergencies, and registered breeding holes, which may also be due to low egg hatchability. Compared to other treatments such as neem, malabar nut, and wormwood-treated seeds, Panthee  suggested that A. calamus-treated maize seeds produced a lower weevil population, resulting in fewer exit holes . A similar result was shown by Shrestha  who reported that negligible exit holes in maize kernels were noted in seeds treated with Acorus calamus (rhizome powder).
3.3. Grain Damage
All botanicals used for weevil control had a significant effect on grain damage compared to the control (). The percentage of grain damage was the lowest in the Acorus calamus (1.23%) and the highest in the control (18.0%) after 120 days (Table 3). The present results were supported by the results of Kumar  who found that Acorus calamus rhizome powder gave the maximum seed protection of up to 60 Days After Silking at a rate of 1%. In the current study, seed damage was minimal even after 120 days. This result was supported by Reddy and Reddy . According to Kudachi , seeds treated with Acorus calamus rhizome powder @ 1% were significantly better without damage to the seeds, but untreated control seeds suffered the most (82%). GC  also found that the Acorus calamus (50 g·kg−1) was the most effective, and least damaging plant against maize weevil over a nine-month period. This research is backed by Paneru and Thapa's  findings that Acorus calamus rhizome powder caused negligible grain damage during storage.
3.4. Weight Loss
The weight loss was adjusted for the loss of moisture for each treatment. The highest weight loss due to moisture loss (%) was observed in plant-derived cereals compared to the control. Similarly, significant weight loss due to weevil was observed in plant-derived cereals compared to the control () (Table 4). The lowest loss due to weevil was observed in maize seeds treated with Acorus calamus (0.36 kg), while the highest loss was observed in the control (3.33 kg) at 120 DAS (Table 4). The highest loss in control was due to the consumption of grains by the weevil. These findings are supported by Paneru et al. , Jilani , Biradar , and Kumar  who found that Acorus calamus was a good preservative with a long-lasting effect on mung beans. Kalasagonda  confirmed these results by stating that the weight of wheat grain did not decrease at a concentration of 0.8%. Acorus calamus (30 g·kg−1) in corn grains caused the least damage, and at the same time, the least weight loss on the shallow and moderate sloping slopes of Nepal . Accordingly, Regmi et al.  came to the same conclusion and reported that seeds treated with Acorus calamus lost little weight in a basement.
Among several plant materials tested, Acorus calamus (rhizome powder @ 5g·kg−1 maize seed) significantly reduced weight loss, amount of grain damage, number of holes, and weevil population. Thus, this finding helps to develop a storehouse based on the integrated pest management model that could represent an environmentally sound, economically viable, and socially acceptable approach in the rural area of Nepal.
Data will be made available upon request.
Conflicts of Interest
The authors declare that there are no conflicts of interest regarding the publication of this paper.
Bishnu Prasad Neupane conceived and designed the experiments, performed the experiments, analyzed, and interpreted the data, and wrote the paper. Prem Nidhi Sharma, and Sunil Aryal gave guidance, monitored the experiment, and reviewed the initial draft of the manuscript. Jiban Shrestha reviewed the initial draft of the manuscript, and contributed to the analysis of the data.
This research was supported by the fund of the National Entomology Research Centre, Khumaltar, Lalitpur, Nepal.
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