Sitophilus zeamais (Motschulsky): the primary obstacles in the maize quality and quantity

One of the main obstacles to maize farming is the extensive loss of yields caused by the investment of the Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) during the storage period. This pest attacks maize kernels in the active larval stage; they burrow, attack, and hide in seeds. Some research reports that this pest attack can cause damage between 18-20%; in conditions of high water content, the damage rate can reach 30-40%. In addition to direct damage, this pest attack can reduce product and nutritional quality, seed weight, and the percentage of germination, which will reduce market value. Besides being able to cause severe damage to maize kernels, this pest also attacks several other agricultural products in stockpiles, such as sorghum, rice, wheat, and processed food products such as pasta and biscuits. This paper reviews several significant research results on the insect pest Sitophilus zeamais Motsch. In the future, it is hoped that it will provide helpful information for researchers and academics everywhere.


Introduction
Maize, one of the most important crops in the world, is easy to adapt and cultivate so it can be planted in any agroecological conditions of the land, such as dry land, paddy fields, swampy land, and tidal land, with various types of soil and climate [1,2].The production of maize is utilized as livestock feed and human food.The nutritional ingredients of maize are 72% starch, 10% protein, and 4% fat, energy supply 365 Kcal/100 g.Several products of maize as the main ingredient such as flour, sweeteners, oil, beverages, glue, industrial alcohol, and fuel ethanol [3,4].The average price of maize has increased, with an average price update in June 2022 reaching USD 335.71/ton.International maize prices reached their highest price in April 2022 of USD 348.17/ton and tended to experience a slight decline until June 2022.The tendency for world maize prices to improve in January-June 2022, which rose by 21.53% compared to the same period in 2021, is an opportunity for Indonesia to export maize [5].
In Indonesia, based on the Ministry of Agriculture and Statistics Indonesia data, the national maize production area from January to December 2021 is 4.15 million hectares, net production is 15.79 million tons with a moisture content of 14%.Meanwhile, the annual need for for feed, consumption, and the food industry totals 14.37 million tons, so by adding 1.43 million tons at the end of December 2020 (carry over) stock, a 2021 maize stock of 2.85 million tons was obtained [5].The estimated production results will increase by an average of 9.29% per year and consumption will increase by an average of 4.38% per year [6].Maize contains bioactive components that provide multifunctional physiological effects for the body, including strengthening the immune system, regulating the rhythm of physical conditions, slowing down aging, and helping prevent disease.Several bioactive ingredients such as phenolic acids as the major chemical compound, flavonoids, carotenoids, vitamin E, and phytosterols [7][8][9].In different maize endosperm, the content of calories, water/ash, total carbohydrate, sugar, total fat, protein, calcium, iron, magnesium, niacin, potassium, riboflavin, thiamine, sodium, Vitamin A, Vitamin C, and Zinc will be different [10,11].The different amounts of those nutrients will have different reactions and benefits on the consumer's body.The effort to achieve maize variety with several nutrition adjustment such as quality protein maize (QPM) several research have been published to reach the goals.Jilo (2022) [12] mentioned that in developing QPM, both conventional and molecular breeding technique successfully develop QPM maize for better nutrition compound to enhance the malnutrition especially in developing countries.
In terms of plant cultivation, the main obstacle to maize farming is the loss of yields due to infestation of maize weevil or Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) during the storage period, especially in farmers' storage warehouses [13][14][15][16].This pest has a very large destructive ability to attack maize kernels in the active larval stage.At this stage, the larvae burrow, attack the seeds, and hide inside the grain [17].This pest is commonly found in tropical and subtropical climates where its food preferences tend to be polyphagous, which can attack several agricultural products in storage (food stock) such as maize, sorghum, rice, wheat and processed food products, such as pasta and biscuits [18,19].In the active vegetative stage of maize plants, this pest can even attack cobs since they are still in the main crop on varieties with a rudimentary cover of husks [20,21] This paper is written as a review, which results from a desk study of several important previous research results on the insect pest S.zeamais.Hopefully, this paper can provide useful information for researchers and academics.

The potential of Sitophilus. zeamais Motsch pests to cause damage
There are three Sitophilus species namely S. granarius, S. oryzae, and S. zeamais.The Sitophilus sp. will do the infestation inside the kernel [22][23][24].The reproductive potential is very large, where a female insect can lay 150 eggs in the range of 119-120 days.Eggs are laid all over the inside of the kernels but generally near the maize cob.The maximum number of eggs laid per female insect is 300 eggs and the eggs hatch into larvae after 5-6 days [25][26][27].In a few days, the eggs will hatch into larvae, and the larvae burrow into the core of the maize kernels.Larvae are stout and dense, legless, white in color, and have a brown head about 4 mm long.The larval stage is around 25-30 days, while the larval stage is between 3-4 weeks.After the larval phase ends, the larva turns into a pupa [22,24,28,29].Pupae are white with a length of 3-4 mm.The pupal stage lasts 5-8 days, with an average of 6 days.Furthermore, the will continue to develop to adult.Adults have a life span of 4-5 months when food is available and approximately 36 days without food.The life cycle is approximately 30-45 days at optimum temperature conditions of 29 0 C, 70% relative humidity, and 14% seed moisture content.The population grows very fast if the material stored has a moisture content above 15% [30][31][32].
Yield losses at each stage of post-harvest handling varied according to the region and production system.The results showed that the storage stage is the most critical, and this species is the main pest that cause serious problems, resulting in a drastic reduction in production.In the active vegetative stage of maize plants, this pest can even attack cobs from when they are still in the plantation (in the field), especially on varieties with a rudimentary covering of the husks [31][32][33][34][35][36].

Economic Entomology
The damage to the products or stored materials has a significant impact on economic value because these materials are ready for consumption and have cost a lot of money from stages of seedling, tillage, planting, maintenance, and harvest.In other words, a small amount of damage to the product can result in a large loss compared to a pest attack on a crop.S. zeamais attacks will reduce the quality and quantity of materials, such as discoloration, taste, odor, and even disease contamination carried by this species, such as aflatoxins.This pest attack can reduce nutritional quality, seed weight, and germination percentage, reducing market value [37,38].The attack on maize kernels can drastically reduce weight, while the decrease in rice is quite mild [39].Based on the range of damage percentages, the economic losses from this pest attack are very large when calculated on a national scale [25,30,40].

Impact of Attack on the Quality of Maize Kernels
Insect host preferences are based on several factors such as varieties, size, color and others.A potential varieties can suppress the offspring of S. zeamais because lack of nutrient for the adult cause the death of the insect adult [41,42].For the chemical compound in the maize, several bases were found to increase the resistance of the maize such as fibre, phenolic acid, and trypsin inhibitor.However, protein, zinc, magnesium, calcium, sodium, phosphorus, manganese, iron, cobalt, and starch tend to increase the susceptibility of the S. zemais to infest the maize [43].The appearance of the seed also determines the feeding preferences.Based on Groote (2017) [44] both S. zeamais and Prostephanus truncatus have preference feeding on smaller seed than the larger seed while the adult will prefer the larger seed for the oviposition.Furthermore, the green color will attract S. zeamais to feed on the seed and caused 56% weight loss compared to the clear grains (33%).The S. zeamais caused seed damage and weight loss in Bangladesh with 75.85% quantitative grain damage and 51-85% loses after 6 months storing.This massive destruction by S. zeamais need an integrated techniques to control and suppress the insect`s population [45].The maize kernels quality decreases depending on the severity of the insect feed on the kernel.The symptoms of the attack are in the form of drilled holes made by insects while feeding and the result of grinding is in the form of flour, can stick to the granules due to the saliva of the larvae, causing the quality of the seeds to decrease.Other than that, then the drill hole can be placed for the adult to laying the eggs by closing the hole using flour from grinding which can stick together due to the gelatinous substance secreted by female imago [46,47].

Impact of Attacks and Contamination on Food Safety
Powder is one of the characteristics and traces of attack by S. zeamais in the field.As a result, the food will be polluted, and the quality will decrease as the moisture content in the seeds increases.This condition will stimulate harmful microorganisms, which can reduce the quality of food ingredients and trigger the growth of mycotoxins or other microorganisms in the surrounding environment.Some harmful microorganisms often found in maize kernels attacked by maize weevils are myxotoxins.Mycotoxins are toxic substances produced by fungi, a group of secondary metabolites produced by molds that cause toxic responses in humans and animals when consumed.Meanwhile, Aflatoxins are secondary metabolite compounds, which are always an important problem since their existence is a serious problem in the food sector throughout the world in particular regions [38,[48][49][50] Mycotoxins produced by several genera of fungi Fusarium, Aspergillus, Rhizopus, Claviceps or Alternaria and Penicillium [51][52][53][54][55][56][57][58][59][60].There are hundreds of mycotoxins that affect the environment.Several mycotoxins that effect to the health are Aflatoxins, Ochratoxin A, Fumonisins, Deoxynivalenol, Trichothecenes, Zearalenone, and Patulin [54].The harmful impacts to the human health such as Carcinogenic, teratogenic, hepatoxic, mutagenic, immunosuppressive effects liver carcinogen genotoxic, Nephrotoxic, CIT-mediated oxidative stress, mitochondrial dysfunction, weak genotoxic effect, reproductive toxicity teratogenic, embryotoxic effects, nausea, vomiting, diarrhea, abdominal pain, headache, dizziness and fever [51,54,61].Aflatoxin B1 (AfB1) can be found in many food and ingredients that become world health problem because the toxicity caused the cell mutation and trigger cancer cells.The contamination levels for maize products in Indonesia from 0.3 to 6171 ng g −1 [60].The levels of AfB1 contamination found in the maize and peanut products from Indonesia appear to be similar to contamination levels reported for maize and peanut products from other Southeast Asian countries [59].
The maize weevil S. zeamais related to mycotoxin contamination which is influenced by environmental conditions.Mycotoxins can be found when maize was infested with the S. zeamais and had Aspergillus flavus inoculum.It should be noted that A.flavus alone does not support mycotoxin production in maize samples without insects and invasion.The rapid dispersal and growth of mycotoxins can result from the larvae distributing the fungal spores and increasing the surface area on which the fungus can develop and produce more mycotoxins.In addition, insect metabolism causes an increase in temperature and moisture content of the substrate which supports the development of fungi and the production of mycotoxins [62,63].High humidity and suitable provides ideal conditions for fungal proliferation and mycotoxin accumulation.To reduce the path from mycotoxins in the food and feed chain, it is necessary for dealing with insect pests and fungal contamination [61][62][63][64].

Countermeasures
To prevent maize weevil, it is important to teach farmers about the maize post-harvest processing stages based on the stages in the standard references.The flow or stages are already a selection process to produce good and quality beans, starting from the stages of harvesting, stripping, and maintaining the moisture content of the maize kernels.Moisture content is a physical component that significantly influences the rate of infestation of stored materials.As a result, serious efforts must be given to other than storage temperature, material quality, air humidity, sorting, and drying.Moisture content also affects the development of warehouse insect pests, seed age, and mechanical damage.Moisture content is one of the factors that affect the ability of seeds to maintain their viability within certain limits Several techniques and technologies have been established to minimize the production loss due to insect invitation and mycotoxin contamination.Integrated management that can be applied by the farmers such as using biopolymer films and coatings as packaging incorporating antimicrobial agents provide great potential for controlling common fungi and mycotoxins and enhancing food quality and safety [69].Other than that, nitrogen controlled atmosphere could be projected to a large-scale system for grain to avoid or reduce chemical treatments and control the mycotoxin contaminant [70].

Conclusion
Maize weevil has an impact on food contamination by insect feces and webbing (dead insect body parts), which results in a decrease in quality, taste, and market value, results in an unpleasant odor, and triggers the growth of other microorganism contaminants such as mycotoxin fungi, and the most dangerous is aflatoxin.Several technologies have been developed to control the spread of mycotoxins and the infestation of S. zeamais.Environmental control with several integrated management will reduce the production loss and minimize the use of chemical control stuff.