Over the last few decades, the human population has grown incessantly, and it is estimated that by the end of this century the population will reach 12.3 billion ^[1][2][1,2]. According to Roser et al. [1], the global population will approach nearly 10 billion by the year 2050, highlighting the crucial role that the food production industry, especially animal protein production, will play in ensuring food and nutrition security. In order to fulfill the food demands of such a large population, a substantial quantity of high-quality food is needed. Poultry eggs and meat can fulfill the protein needs of people and are affordable food sources with a short-term production cycle. Therefore, the future will face a continued demand for poultry feed. Poultry meat is the most economical and consumable source of animal protein for many communities globally, as noted by Asghar et al. [3]. The feed market in the Asia-Pacific region is projected to reach140 billion USD by 2024 [4]. Nevertheless, the escalating costs of poultry production, caused by the increasing expense of feed, pose a risk to the sector, as observed by Naımatı et al. [5]. However, as the demand for products derived from poultry grows, feed resources may become limited to sustain such growth in poultry production and operations, as observed by Thirumalaisamy et al. [6].

Soybean and fish meals, which are conventional protein sources, have been associated with notable environmental concerns such as greenhouse gas emissions, deforestation, and water pollution. As a result, an increasing interest has emerged in using alternative protein sources, including plants and animal-based proteins (insect meal) ^[7][8][7,8]. Plant-based proteins are becoming increasingly popular as an eco-friendly substitute for traditional sources of protein for livestock. Soybean-based meal is one example, used as a common source of protein in livestock feed, accounting for around 65% of the global proportion of protein meal production attributed to soybean meal based on the available data and industry reports [9]. Moreover, researchers have been exploring alternative plant-derived protein sources, such as canola, peas, and algae. Pea protein, for example, is abundant in indispensable amino acids with a lower environmental impact than soybean production ^[10][11][10,11].

The market for protein ingredients has grown significantly in recent years, with a projected value of 38 billion USD in 2019. It is projected to experience a growth rate of 9.1% from 2020 to 2027 [12]. Animal protein consumption has significantly increased in recent years, driven by factors such as population growth, urbanization, and rising incomes in developing nations [13]. Based on a study published by the United Nation Food and Agriculture Organization, the global meat demand is projected to increase by 1.3% per year over the next decade [9]. Protein is an essential nutrient for poultry, and traditional protein sources such as soybean and fish meal have several disadvantages, including the high cost of fish meal, limited availability, and long term availability concerns. The utilization of soybean meal (SBM) in poultry rations is prevalent, primarily attributed to its improved crude protein content and amino acid profile [14]. Protein is the second most important component in the diet of poultry. In light of the price fluctuations of SBM and the continuous rise in feed costs, researchers have been investigating alternative sources of protein. The substitution of SBM with alternative sources of protein in poultry meals has the potential to alleviate the competition between humans and livestock for soybean resources and to enhance the output of animal protein [15]. Legumes, cereals, and seeds are essential plant protein sources for humans, especially in a vegetarian diet. Meat and bone meal is often used in poultry diets; however, it is less digestible than soybean meal. In light of the particular dietary requirements of poultry, the digestibility of protein sources is an important element to consider [16]. Therefore, we need to find ways to increase insect-based protein diets without causing harmful effects on the environment. To utilize feed additives in chicken feed without negatively impacting the environment, it is critical to carefully choose and control the chemicals and implement advanced farming strategies to monitor and comply with environmental rules. Numerous ranges of feed additives that possess favorable nutritional benefits for poultry have been previously documented in the literature ^[17][18][17,18].

In recent times, insect meal as a source of protein in poultry diets is gaining attention, which has the potential to lower feed costs and boost profitability via the utilization of fresh insects for small-scale poultry production ^[19][20][19,20]. Insects offer a promising and subsistence solution for addressing the challenges associated with conventional protein sources, while providing comparable nutritional value and a reduced environmental footprint ^[21][22][21,22]. The contribution of poultry to the economies of many developing countries is significant and supports the livelihoods of many individuals, especially in rural areas [23]. Consuming poultry products, including meat and eggs, is a significant means for humans to acquire animal protein [24].

Insect meal is another alternative protein source that has attracted interest nowadays. It has been found that insect meal is a reliable source of protein for animal and poultry feed, with research indicating that it can improve animal growth and reduce feed conversion ratios [25]. It is believed that insect meal offers a potential alternative protein source in feed. Moreover, there is a need to overcome some obstacles, such as regulatory constraints and consumer acceptability. However, the utilization of insects in livestock feed is already permitted in some countries, including the European Union and Canada [26].

The usage of poultry meat, particularly chicken, is predicted to keep rising in the next ten years, as it is currently the most popular white meat ^[3][27][3,27]. Poultry production is considered to have a relatively low environmental impact in comparison to other meats because it does not produce enteric fermentation and has a lower feed conversion ratio (FCR) [28]. While there are benefits to raising poultry, such as their efficient use of resources and faster growth rate, the costs of production are increasing. The high costs of poultry production can be attributed to various factors, with the cost of feed being one of the primary factors that accounts for a considerable portion of the overall production cost [29]. The primary reason for the high cost of poultry feed is the production and processing cost, market demand, and supply of soyabean globally [30]

Furthermore, the competition for limited resources among the food, feed, and fuel sectors, along with the impact of changing climatic factors, has significantly influenced the access to conventional feed ingredients such as soybean, fish meal, and cereals. This has resulted in a decrease in accessibility and a high level of volatility in feed resource prices, as highlighted by Mugwanya et al. [31]. In the last ten years, the lack of traditional feed resources has caused an increase in feed prices, making it necessary to search for alternative protein sources for poultry. The usage of insects as a source of feed for farmed animals holds great promise due to the nutritional benefits (essential amino acid profiles and high protein contents) of insects and possible environmental advantages of this farming practice, which mainly depends upon the substrate used for insect rearing and its impact on the quality of the insect meal, according to van Huis et al. [25]. However, Western customers do not generally agree regarding the consumption of insects. It is possible to collect insects in the wild or rear them commercially at a low cost, with a shorter production cycle, as noted by Oonincx et al. [32]. Although the natural harvesting of insects may be practical for small-scale or subsistence farming, commercial-scale insect production at a constantly low cost is still under consideration. The consumption of insects in human food has been prevalent in tropical countries for centuries, as stated by DeFoliart et al. [33]. In addition to serving as a source of protein, the fat collected from insects in the meal process of extraction can be utilized in the diets of chicken, reducing the need for soybean and various vegetable oils, according to ^[4][34][4,34]. As a result, the recent research has aimed to assess possible alternatives, including insects ^[35][36][37][35,36,37], bacteria ^[35][38][35,38], and organic by-products ^[39][40][39,40]. Insects gained the most attention among them because of their widespread usage in poultry feed and their easy production [41]. Common house flies, black soldier flies, yellow mealworms, and blowflies are among the insects that are the potential alternatives for protein sources in poultry diets, as highlighted by Čičková et al. [42]. Insects have high mineral contents, including zinc (Zn) and iron (Fe), as noted by Finke et al. [43], and contain an array of vitamins, including riboflavin, folic acid, cyanocobalamin, thiamine, and retinol traces, as described by Rumpold et al. [44]. Insects additionally possess a particular kind of peptide that shows an antioxidant action, which can be beneficial for the health of livestock, according to Schiavone et al. [45]. Water-soluble products based on insects exhibit exceptional antioxidant properties and have free radical neutralization characteristics, setting them apart from various plant- and animal-derived protein hydrolysate products, as observed by Di Mattia et al. [46].

2. Insect Meal as a Sustainable Nutrient Source in Poultry Diets

The consumption of poultry products is predicted to rise in the coming years; therefore, there is a significant need for novel feed ingredients that can sustainably facilitate intensive poultry production ^[47][48]. Insects constitute a high-quality protein source, being rich in essential amino acids and lipids. Interestingly, the protein contents of insect meals can significantly vary, ranging from almost 40% to 60%, even if being derived from the same insect species ^{[7][8][48][49]}[7,8,47,49]. The variance in nutrient contents can also be influenced by factors such as dietary habits, including the specific types of food they consume in their ecological niche (preferably natural feeding patterns, and how these aspects affect the nutrient content and overall nutritional profiles of insects), developmental stage, and prevailing environmental conditions, thereby leading to dissimilar nutritional profiles even amongst closely related insect taxa [50]. The protein makeup of dried insect matter varies significantly among different insect species, ranging from 35% in termites to as high as 61% in crickets, grasshoppers, and locusts, with some species exhibiting even higher protein contents of up to 77% [44]. The majority of edible insect species exhibit adequate levels of essential amino acids, including tyrosine, tryptophan, phenylalanine, lysine, and threonine, as per the recommended dietary requirements. It has been shown that the edible insect species possess sufficient quantities of these important amino acids, making them possibly beneficial for poultry ^[7][51][7,51]. Insects primarily store carbohydrates in two forms: chitin and glycogen [52]. Chitin, which constitutes the main component of their exoskeleton, is a polymer of N-acetyl-D-glucosamine [53]. In contrast, the muscle cells of insects store glycogen as an energy source. Edible insects contain varying amounts of carbohydrates (mealworms: 14–18%; crickets: 10–20%; grasshoppers: 11–21%; silkworm pupae: 10–20%; ants: 2–15%) ^[54][55][56][54,55,56]. However, the specific carbohydrate content can depend on factors such as the insect species, diet, and developmental stage ^[44][57][44,57]. The application of insects in different forms as a potential alternative source of protein and carbohydrates in poultry feed is shown in Figure 1. Insects have been found to contain a variable contents ranging from 2% to 62%, with high amounts of unsaturated fatty acids constituting up to 75% of the total fatty acid content. Although the vitamin content of insects is not particularly high, they do contain notable amounts of vitamins A, C, D, and E ^[58][59][60][58,59,60]. Insects such as crickets and termites have varying mineral contents, with some being high in magnesium, zinc, and copper, while others such as grasshoppers and mealworms have higher levels of copper, magnesium, manganese, and zinc than beef. However, insects are usually low in sodium, calcium, and potassium ^[61][62][61,62]. The substantial amounts of indispensable amino acids, mineral substances, and vitamins make insect meal a prospective competitor to conventional protein sources such as fish meal and soybean [39]. The nutritional compositions of different insect species are shown in Table 1.

Insects Species	Nutrient and DM %	Insect Life Stage	Method of Processing	Reference
Mealworm (Tenebrio molitor)	DM (97.02), CP (53.83), EE (28.03), Ash (6.99), CF (7.53), Chitin (5.6), GE (2.8), Ca (0.06), P (1.10)	Larvae	Degutted, freeze-dried	[63][64][65][63,64,65]
Field cricket (Gryllus bimaculatus)	CP (58.3), CF (9.5), EE (11.9), Ash (9.7)	Adult	Degutted, freeze-dried	[39][66][39,66]
Black soldier fly (Hermetia illucens)	CP (42.2), Chitin (5.6), EE (21.8) Ash (10.0), Ca (7.00), P(1.00) K (0.69), Na (0.13), Mg (0.39), Fe (0.14), Mn (246), Zn (108), Cu (6.0)	Prepupae	Whole, freeze-dried	[64][67][68][69][64,67,68,69]
House fly (Musca domestica)	CP (55.4), Chitin (6.2), EE (20.8), Ash (6.2)	Larvae	Meal, oven-dried for 2 days	[70]
Earthworm (Lumbricus terrestris)	CP (63.0), CF (5.9), Ash (8.9) Na (0.43), Ca (0.53), K (0.62) P (0.94), GE (1476kJ/100g)	Adult	direct heating or freezing before drying	[71][72][71,72]
Silkworm (Bombyx mori)	CP (23.1), CF (14.2), Moisture (60–70), Ash (1.5), GE (229 kcal/kg)	pupae	Sun dried, powdered	[73][74][73,74]
Grasshoppers (Caelifera (Suborder)	CP (28.13), CF (2.38), Ash (9.97) EE (4.18), GE (1618 kcal/g)	Larvae	Degutted, freeze-dried	[75]
Locust (Schistocerca gregaria)	CP (52.3), EE (12), CF (19), Ash (10.0)	Larvae	Degutted, freeze-dried	[76]
Crickets (Gryllus testaceus walker)	CP (58.3), EE (10.3)	Larvae	Degutted, freeze-dried	[77]
Westwood (Cirina forda)	CP (20.0), EE (12.5), Ash (8.7) carbohydrate (54.3), K (47.6) P (45.9), Na (44.4), Mg (43.8), Zn (24.1), Ca (12.8), Fe (1.2)	Larvae	Degutted, freeze-dried	[78]
Mopane worm (Gonimbrasia belina)	CP (55), Ash (5.8), Lignin (5.2), N (9.0), Fat (16.7), K (35.2), Ca (16.0), P (14.7), Mg (4.1, Fe (12.7) Zn (1.9), Na (33.3)	Larvae	Freeze-dried	[79]