Investigating the Influence of Fly Attractant on Food Waste Recovery through Fly Larvae Production

Abstract

The food industry is one of the sectors that produces considerable amounts of solid waste on a daily basis. Handling such waste has been a significant issue of worldwide concern. As a result, research into developing low-cost and effective technology for the recovery of food waste is critical in order to keep pace with the rapidly developing world. This research investigated the potential of maggot production on the recovery of food waste. Four different food waste materials (banana, starch, pineapples, and oranges) were taken into consideration. Additionally, the effect of the fly attractant on the production system’s overall performance was assessed; the fly attractant was a mixture of cattle blood and meat waste. With a correlation index of 0.96 (without fly attractant) and 0.87 (with fly attractant), the number of days before harvesting and the average maggot weight had a very high (positive) correlation. Moreover, it was observed that using a fly attractant increased maggot yield substantially. For instance, the banana materials produced up to 94 g/kg of maggot weight on the eighth day, which is approximately a 32.4% increase from the same material without fly attractant. On the other hand, the trials’ relative dry weight reduction ranged from 52.5% to 82.4%. The results of this study also showed that producing maggots can be a practical method for recovering food waste, particularly when combined with the use of a fly attractant. The residue from the maggot production process can be applied as an organic fertilizer.

1. Introduction

Due to global population growth, the demand for food has also been increasing. However, the growth in food demand has been accompanied by a high production of waste [1,2,3]. In fact, a significant amount of food waste is generated every day worldwide [4].

Unfortunately, the capacity to handle such a massive waste is also severely limited by financial resources [5,6]. There is a range of strategies for dealing with food waste that is currently in use, including landfilling [7], composting [8], food waste disposer [9,10], and direct anaerobic digestion [11]. However, each food waste management approach is linked to a number of drawbacks. For instance, landfills have been widely used for the disposal of food waste [12,13,14]. However, the challenge is that food waste in landfills rots and produces a large amount of methane, a highly powerful greenhouse gas [15]. Excessive levels of greenhouse gases like methane, carbon dioxide, and chlorofluorocarbons heat the earth’s atmosphere by absorbing infrared radiation, which contributes to global warming and other types of climate change [16,17,18].

As a result, for the protection of human health and the environment in general it is critical to explore and develop readily available, cost-effective, and environmentally friendly technologies for the recovery of food waste. As one of the most valuable and limited resources, proper food waste management can also assist to safeguard water resources from pollution. Maggot production as animal feed stands to be among the relatively cost-effective approaches for food waste recovery [19,20,21]. Maggots can be defined as fly larvae, typically of the common housefly as well as the bluebottle species [22]. The production mechanism is that flies are attracted to food and other sorts of rubbish, they then lay their eggs on the rubbish, the latter eventually hatching into maggots [23]. Regrettably, the information on how maggot production can be a useful tool for food waste management is still scarce.

The flies can effectively convert organic waste into a protein-rich end product that is an excellent source for animal feed [24]. The most prevalent application is as a source of protein for chickens. The larvae can also be processed to separate the protein, which can subsequently be used in animal, poultry, and fish feed. The maggot feces can be used as landscaping compost. In that matter, the leftover product remaining from the decomposition process can be a high nitrogen organic fertilizer. For example, it is estimated that to produce 1 kg of farmed fish in any aquaculture system, 1–8 kilos of feed are required [25]. In the field of fish farming, the fish feed is made up of raw materials, such as straw meal [26], soybean cake [27], peanut cake [28], corn protein powder, rice bran [29], and wheat bran [30], which in turn has been increasing raw material competition. Moreover, raising chickens on poultry farms is equally challenging at the moment due to the high feed demand [31]. It is estimated that chickens require double the amount of grain in comparison to the meat they produce [32]. In general, the demand for feed has made nearly 40% of all grain produced in the world end up as animal feed [33].

Many factors can affect the productivity of maggots [34,35] including factors related to the substrate’s initial conditions and the type of material used for the production. Unfortunately, there are insufficient studies to provide enough information on how these factors would affect the productivity of maggots on different food waste materials. Additionally, the information on the potential of maggot production for waste recovery and reduction based on different substrate materials is still scarce. Unlike fruit flies, which like sweet foods and are more frequently attracted to overripe fruit, spilled soda, and alcohol, ordinary house flies are drawn to decaying organic waste, such as feces and rotting flesh. Therefore, using a fly attractant has the potential to increase the number of flies attracted to the substrates and increase system productivity.

This study investigates the potential of recovering food waste through maggots’ production. Different factors, such as time and application of fly attractants to maggot production, are also investigated. The experiment uses four different types of food waste (starchy food leftovers, rotten bananas and peels, pineapple peels, and rotten oranges). The breeding vats are divided into 5-day harvesting, 6-day harvesting, 7-day harvesting, and 8-day harvesting. In addition, the amount of waste reduced by maggots from the investigated substrate materials is computed to investigate the potential of maggot production for organic waste reduction. Furthermore, box and whisker plots are developed to evaluate the data distributions among the selected maggot production parameters.

2. Materials and Methods

2.1. Material Collection, Processing, and Experimental Setup

The substrate materials were grouped into four categories; starchy food leftovers (such as potatoes, bread, rice, pasta, and cereals), rotten bananas and peels, rotten pineapples and peels, and rotten oranges. The materials were collected from different parts of Dar es Salaam, including restaurants and markets. Dar es Salaam is a city (and a former capital city) in Tanzania, remaining the largest city in the country by population.

The materials were grouped accordingly and ground into smaller particles using a grinding machine. In addition, the materials were properly mixed before introducing them into the breeding vats. A general flowchart provides a summary of this process in Figure 1. To get rid of any potential fly eggs or larvae that might have been present in the substrate when collecting the materials, all of the substrates utilized in this study were placed in an airtight container for more than 12 h before the studies began.

For all of the experiments, a substrate of 2 kg was used. For the substrates containing fly attractants, approximately 10% of the substrate weight of fly attractants composed of thoroughly mixed cattle blood and decomposing meat waste were thoroughly mixed and placed randomly in the breeding vats. The selection of the fly attractant is based on the fact that decomposing organic filth, such as rotting meat, has a tendency of attracting common house flies. The breeding vats were then exposed for approximately 8 h to attract houseflies as a process of naturally laying their eggs. After exposing the breeding vats, the substrates were covered using perforated polythene cover to provide shading. To make sure that moisture is maintained in breeding vats, water had to be sprinkled at least once per day.

In general, the study had two main cases: case number one was based on the group of substrates that was cultured without adding fly attractant, while case number two was based on the group of substrates mixed with fly attractant. Both cases were investigated under 5-day harvesting, 6-day harvesting, 7-day harvesting, and 8-day harvesting. Fresh organic substrates were collected across the city, including starchy food leftovers (such as rice and bread), rotten bananas and peels, rotten pineapples and peels, and rotten oranges.

In general, a regular sprinkle of water (at least twice a day) was used to keep the substrates moist. Maggots were manually collected (completely separated from the residue), cleaned, blanched with hot water, and then weighed to determine the total maggot weight from each substrate.

2.2. Material Characteristics

Moisture (water) content, pH, chemical oxygen demand (COD), temperature, and organic matter content were among the parameters investigated in the prepared materials before breeding. The analyzed waste materials’ concentrations of the aforementioned parameters varied slightly from one sample to the other. In general, from all the investigated materials, pH ranged from 4.2 to 9.5, with the lowest pH observed from the orange and pineapple materials. The acidic nature of the pineapple can be linked to the presence of bromelain (a corrosive chemical that breaks down amino acids. Whereas, on the other hand, the acidic nature of the orange materials can be linked to the fact that oranges are characterized by the possession of a high vitamin C (ascorbic acid) concentration, making them relatively acidic.

To be more specific, the moisture content in the starch materials ranged from 64.6% to 88.5%, while pH ranged from 6 to 9.5, COD ranged from 4865 mg/L to 9451 mg/L, temperature ranged from 19.4 °C to 30 °C, and organic matter was observed to range from 68.8% to 90%.

Additionally, the moisture content in the banana materials ranged from 79.9% to 91.1%, pH ranged from 7.2 to 9.9, COD ranged from 5209 mg/L to 10248 mg/L, temperature ranged from 20.2 °C to 28.5 °C, and organic matter was observed to range from 89.9% to 95.6%.

On the other hand, the moisture content in the pineapple materials ranged from 80.4% to 92%, pH ranged from 4.4 to 5.8, COD ranged from 6544 mg/L to 9552 mg/L, temperature ranged from 21.6 °C to 29.9 °C, and organic matter was observed to range from 92.3% to 95.2%.

The moisture content in the orange materials ranged from 84% to 90%, pH ranged from 4.2 to 6.8, COD ranged from 4469 mg/L to 11,425 mg/L, temperature ranged from 20 °C to 30.5 °C, and the organic matter content was observed to range from 90.4% to 95.9%.

As previously highlighted, the breeding vats were divided into: 5-day harvesting, 6-day harvesting, 7-day harvesting, and 8-day harvesting, whereby the pH in the substrates was measured using conical-tip electrodes (Mettler Toledo, Columbus, OH, USA). The COD in the samples was measured using the Optimized APHA Standard Method 5220 D-Closed Reflux Colorimetric for COD determination of solid samples [36]. The Walkley and Black method was used to measure the organic matter in the samples [37], while moisture content determination was based on the simple arithmetic of subtracting the weight of the dry sample from the total weight of the wet sample divided by the total weight of the wet sample multiplied by 100. Figure 2 presents the summary of the material preparation processes.

2.3. Statistical Methods

2.3.1. Correlation Analysis

To investigate the relationship among the studied parameters, correlation matrices were developed. These matrices were important to evaluate the strength of the relationship among the potential selected parameters affecting maggot production. According to the matrices, a high correlation meant that there was a significant association between two or more variables. While a low correlation indicated that the variables had little in common. The interpretation of the correlation indices employed in this investigation is summarized in

Table 1. Interpretation of the correlation coefficients.

Correlation Coefficient	Relationship
Below 0.29	Generally weak
Between 0.3 and 0.49	Moderately correlated
Between 0.5 and 0.69	Strongly correlated
Between 0.7 and 1	Very strong correlation

.

2.3.2. Analysis of Variance (ANOVA)

A single-factor Analysis of Variance (ANOVA) was used to test if the differences between sets of data were statistically significant. This approach takes samples from each group and assesses the levels of variance within them. To be more precise, the p-value and alpha (0.05) were combined to calculate the significance threshold. It should be emphasized that the probability to reject the null hypothesis (even if it is true) is represented by the alpha value. The null hypothesis is accepted if the p-value is larger than the alpha value. On the other hand, the p-value reflects the possibility of obtaining a result that is more extreme than that received from the experiment.

In addition, the T-test (Two-Sample Assuming Equal Variances) was employed to see if there was a significant difference in the means of two groups of each parameter as determined by the two treatment procedures. The degree of the difference in terms of data variation is expressed by the T-value. As a result, the greater the value of T, the stronger the evidence that the null hypothesis is untrue.

Tukey’s HSD (honestly significant difference) test was also used in the study, which is a single-step multiple comparison process. It was applied to identify means that differed significantly from one another.

3. Results and Discussion

3.1. Production Results without Fly Attractant

The investigation of maggot production from food wastes based on the main two cases (substrates without fly attractant and substrates with an application of fly attractant) was successfully executed. The weight of the maggots was expressed in terms of g per kg of dry substrate. The pH levels in the substrates were observed to be fluctuating with no specific trend with time. The phenomenon led to low correlation indices between pH and other parameters. Figure 3 provides a general picture of the maggot production process before and after harvesting.

Time was an important factor investigated for maggot production and waste reduction. In this study, the maggot production is based on four different groups of days starting from day 5. Maggots have been seen to shed their outer covering twice throughout the growth phase and to grow up to 20 mm in length in 4 days, according to the literature [38]. In that matter, upon being supplied with the necessary food nutrients that are also determined by the substrate material, they, in turn, retire into their puparia where the transformation occurs [23].

3.1.1. Correlation Analysis without Fly Attractant

The relationship among the key factors investigated in this study was also checked using correlation matrices.

Table 2. Correlation among maggot weight, number of days to harvesting, and pH from substrates without fly attractants.

Parameter	Number of Days	Average Maggot Weight	pH
Number of days	1
Average maggot weight	0.96	1
pH	0.66	0.66	1

shows that when the substrates were cultivated without the use of a fly attractant, the number of days to harvesting and the average maggot weight had a “very strong” (positive) correlation, with a correlation index of 0.96. However, the correlation between pH and weight of the maggots and the number of days is somewhat less, and this is probably due to the fact that pH did not change for some of the days, especially during the last days when pH remained almost constant while the weight of the maggots was changing. The observation reported in this study is similar to the study that investigated the impact of pH and feeding system specifically on black soldier fly (Hermetia illucens, L.; Diptera: Stratiomyidae) larval development conducted by Marco Meneguz, Laura Gasco, and Jeffery K. Tomberlin [39]. In that study, it was observed that pH treatments impacted larval weight on some of the days but not at the end of the trial.

3.1.2. Average Weight Characterization without Fly Attractant

The weight of the maggots is expressed in grams per kilogram of the dry substrate. The number of days had a substantial effect on the average weight of the maggots, as seen in Figure 4. However, the extent to which the number of days affected the maggot weight differed depending on the type of substrate used. In this study, a gradual effect was observed from starch materials, with a more significant effect observed from banana and pineapple materials, especially during the 7th and 8th day of the trial. On average, the highest average weight of 63.5 g/kg was achieved from the banana materials followed by 62.5 g/kg from pineapple materials during the 8th day of the trial. However, the lowest maggot weight of 36 g/kg can be observed from the 5th day of the trial under starch materials without fly attractant. In the literature, general feeding conditions, including the type of substrate material, have also been observed to be among the crucial decisive factors for maggot production as it affects nutrition during the larvae development phase [40].

3.2. Production Results with Fly Attractant

3.2.1. Correlation Analysis with Fly Attractant

Similarly, as observed in the substrates without fly attractant, a strong relationship (positive correlation) between the number of days to harvesting and the average maggot weight can be observed with a correlation index of 0.87 (

Table 3. Relationship among maggot weight, number of days to harvesting, and pH from substrates mixed with a fly attractant.

	Number of Days	Average Maggot Weight	pH
Number of days	1
Average maggot weight	0.87	1
pH	0.77	0.48	1

). However, as previously mentioned, the unpredictable changes in pH led to a moderate correlation between the pH and average maggot weight with a correlation index of 0.48. The phenomenon further reveals that the maggot weight has the potential to increase with the number of days. A similar phenomenon has been reported in the literature, with up to 128 g/kg of maggot weight being produced over time in a study conducted by Hezron et al. [41] on the mass production of maggots using manure.

3.2.2. Average Weight Characterization with Fly Attractant

The use of a fly attractant was found to significantly increase maggot yield. Figure 5 shows that on the eighth day of the production process, banana materials produced up to 94 g/kg of maggot weight. This represents a 32.4% increase over the same day, same material, and without fly attractant application. Additionally, roughly 77 g/kg of maggot weight was obtained from the starch materials, which is a 49% increase over the day and the same material when the substrate was cultivated without the use of a fly attractant. However, despite the spontaneous increase in the average maggot weight when the fly attractant was applied to the substrates, the effect of the number of days to harvesting was minimum for some of the materials compared to when the fly attractant was not applied to the substrates. An interesting phenomenon can be observed from day 8 with pineapple materials, where the average maggot weight was reduced by approximately 3%. However, such a phenomenon can be linked to a number of factors, including predation, changes in environmental conditions as well as some unknown potential issues related to the substrate condition on a particular day. In general, it can be stated that the maggot weight during the time of harvesting can be affected by the number of flies attracted to the substrate during the first days of the breeding period. It has to be noted that, over the first days, each female fly can lay up to 500 eggs in multiple batches of 75 to 150 eggs; whereby the quantity of eggs laid is a consequence of female size, which is largely determined by the larval diet [42].

3.3. Analysis of Variance (ANOVA), T-Test, and Tukey’s Honest Significance Difference Test

3.3.1. ANOVA Results

In order to further justify whether differences in the maggot weight data with time from the investigated food waste materials were significant, ANOVA was conducted. A total of 16 input values were taken into consideration for each of the food waste materials used in the study with an alpha value of 0.05.

Table 4. ANOVA results from the substrate without the application of the fly attractant.

ANOVA: Single Factor
Summary
Groups	Count	Sum	Average	Variance
Starch	16	604	37.75	18.46667
Banana	16	925	57.8125	51.09583
Pineapples	16	913	57.0625	44.32917
Oranges	16	897	56.0625	44.0625
ANOVA
Source of Variation	SS	df	MS	F	p-value	F crit
Between Groups	4461.797	3	1487.266	37.66322	8.16 × 10−14	2.758078
Within Groups	2369.313	60	39.48854
Total	6831.109	63

provides a summary of the results of the ANOVA based on substrates that were cultivated without the use of a fly attractant. The Table shows that the p-value for the maggot weight data based on the food waste materials was 8.16 × 10⁻¹⁴. The resulting p-value is less than 0.05, indicating that there are statistically significant differences between the maggot weight data from the analyzed food waste sources.

Other metrics, such as sum, average, and variance, reveal some differences in terms of the materials evaluated in this study, in addition to the p-value. When compared with the other materials, the starch materials have the lowest total, average, and variance numbers. The data also show that in terms of maggot weight, the banana, pineapple, and orange materials outperformed the starch materials. The cause of the phenomenon can be attributed to the flies’ preference for fruits over starchy materials since they require sugar as an instant source of calories to fly [43].

Table 5. ANOVA results from the substrates with fly attractant.

ANOVA: Single Factor
Summary
Groups	Count	Sum	Average	Variance
Starch	16	1326	82.875	32.51667
Banana	16	1464	91.5	65.2
Pineapples	16	1350	84.375	33.58333
Oranges	16	1411	88.1875	44.1625
ANOVA
Source of Variation	SS	df	MS	F	p-value	F crit
Between Groups	724.5469	3	241.5156	5.505806	0.002083	2.758078
Within Groups	2631.938	60	43.86563
Total	3356.484	63

provides a summary of the results of the ANOVA performed using substrates cultivated while a fly attractant was applied. The Table shows that the p-value for the maggot weight data based on the food waste materials was 0.002083. The resulting p-value is less than 0.05, indicating that there are statistically significant differences between the maggot weight data from the analyzed food waste sources. However, it’s worth noting that the p-value obtained from ANOVA on substrates cultivated with fly attractant is larger than that obtained from ANOVA on materials cultured without fly attractant. This behavior also suggests that when the fly attractant is applied to the substrates, the influence of initial material characteristics on maggot production is reduced. Additionally, we may infer from the results that the performance of the maggot production facility is significantly influenced by the initial properties of the substrates. It is also worth noting that flies lay their eggs on decomposing meat due to the fact that it provides a feeding source for the larvae as they develop [44]. When the eggs hatch on the substrate, they start as maggots, which are voracious eaters. To grow and develop into adult flies, these wingless adolescent flies must eat. As a result, when the maggots ingest the substrate, they drastically minimize the amount of waste.

3.3.2. T-Test Results (Two-Sample Assuming Equal Variances)

T-test analysis was used to evaluate the significance levels of the differences between the maggots’ weights of the same material with and without application of the fly attractant.

From

Table 6. T-test results from starch materials.

Material	Starch without Fly Attractant	Starch with Fly Attractant
Mean	37.75	82.875
Variance	18.46667	32.51667
Observations	16	16
Pooled Variance	25.49167
df	30
t Stat	−25.2792
P(T ≤ t) one-tail	4.4 × 10−22
t Critical one-tail	1.697261
P(T ≤ t) two-tail	8.79 × 10−22
t Critical two-tail	2.042272

, it can be seen that a p-value of 8.79 × 10⁻²² was obtained from the T-test; that is simply saying that the null hypothesis is rejected or the differences in terms of the maggot weights between the two sample groups were statistically significant when the calculated p-value was smaller than the alpha value (0.05). Moreover, from the Table, it can be seen that after applying the fly attractant to the banana materials, a mean value of 82.88 g/kg of maggot weight was retrieved, which is approximately a 119.54% increase compared to the mean value obtained from the maggot weight without applying the fly attractant. The findings of this section of the study also show that when a fly attractant is applied to starch-related substrate materials, maggot output increases dramatically. In such a case, in a situation where starch materials are abundant, using a fly attractant at the start of the breeding process can give outcomes that are similar to those produced by fruit materials. Tons of starch-related wastes are generated daily around the world [45], an amount that can be significantly reduced through maggot production.

The T-test from the banana materials yielded a p-value of 2.02 × 10⁻¹³, as shown in

Table 7. T-test results from banana materials.

Material	Banana without Fly Attractant	Banana with Fly Attractant
Mean	57.8125	91.5
Variance	51.09583	65.2
Observations	16	16
Pooled Variance	58.14792
df	30
t Stat	−12.4953
P(T ≤ t) one-tail	1.01 × 10−13
t Critical one-tail	1.697261
P(T ≤ t) two-tail	2.02 × 10−13
t Critical two-tail	2.042272

. In addition, the resultant p-value is less than the alpha value (0.05), implying that the null hypothesis was rejected or that the differences in maggot weights between the two sample groups were statistically significant. Table 7 further shows that after applying the fly attractant to the banana materials, a mean value of 91.5 g/kg of maggot weight was obtained, which is equivalent to a 58.27% increase above the mean value obtained from the maggot weight without applying the fly attractant.

Furthermore, the results from the pineapple materials (with and without the application of fly attractant) were subjected to T-test analysis. The results of the T-test analysis using the pineapple materials are summarized in

Table 8. T-test results from pineapple materials.

Material	Pineapples without Fly Attractant	Pineapples with Fly Attractant
Mean	57.0625	84.375
Variance	44.32917	33.58333
Observations	16	16
Pooled Variance	38.95625
df	30
t Stat	−12.3771
P(T ≤ t) one-tail	1.28 × 10−13
t Critical one-tail	1.697261
P(T ≤ t) two-tail	2.57 × 10−13
t Critical two-tail	2.042272

. It is clear that a p-value of 2.57 × 10⁻¹³ was obtained. The null hypothesis was rejected or the differences in average weights between the two sample groups were statistically significant, as shown by the p-value, which is less than the alpha value (0.05). Similarly, from the mean values, a significant increase in terms of the maggot weight can be observed. Whereas the pineapple materials without fly attractant yielded 57.06 g/kg, a mean value of 84.38 g/kg was obtained with the application of the fly attractant; an increase that is equivalent to 47.86%.

The orange materials were also subjected to a T-test analysis based on the list of maggot weight data without the use of a fly attractant and the orange materials with the use of a fly attractant.

Table 9. T-test results from oranges materials.

Material	Oranges without Fly Attractant	Oranges with Fly Attractant
Mean	56.0625	88.1875
Variance	44.0625	44.1625
Observations	16	16
Pooled Variance	44.1125
df	30
t Stat	−13.6807
P(T ≤ t) one-tail	9.86 × 10−15
t Critical one-tail	1.697261
P(T ≤ t) two-tail	1.97 × 10−14
t Critical two-tail	2.042272

shows that a p-value of 1.97 × 10⁻¹⁴ was obtained using the T-test. The p-value obtained is smaller than the alpha value (0.05), indicating that the null hypothesis was rejected or that the differences in maggot weights between the two sample groups were statistically significant.

3.3.3. Tukey’s Honest Significance Difference (HSD) Test Results

Tukey’s honest significance difference was used to further investigate the significance level of the mean differences in terms of maggot weight from the investigated substrates. From

Table 10. Tukey’s honest significance difference results from substrates without application of fly attractant.

Treatments Pair	Tukey HSD Q Statistic	Tukey HSD p-Value	Tukey HSD Inference
Starch vs. Banana	12.771	0.001	p < 0.01
Starch vs. Pineapples	12.293	0.001	p < 0.01
Starch vs. Oranges	11.657	0.001	p < 0.01
Banana vs. Pineapples	0.477	0.9	insignificant
Banana vs. Oranges	1.114	0.843	insignificant
Pineapples vs. Oranges	0.637	0.9	insignificant

, a significant difference (p < 0.01) can be observed between starch and other substrate materials (banana, pineapples, and oranges), while insignificant differences can be seen among banana, pineapples, and orange materials.

From

Table 11. Tukey’s honest significance difference results from substrates with the application of fly attractant.

Treatments Pair	Tukey HSD Q Statistic	Tukey HSD p-Value	Tukey HSD Inference
Starch vs. Banana	5.209	0.003	p < 0.01
Starch vs. Pineapples	0.906	0.9	insignificant
Starch vs. Oranges	3.209	0.117	insignificant
Banana vs. Pineapples	4.303	0.018	p < 0.05
Banana vs. Oranges	2.001	0.495	insignificant
Pineapples vs. Oranges	2.303	0.372	insignificant

, it can be seen that the application of fly attractant reduced significantly the differences in terms of maggot weight among the investigated substrates, with only starch vs. banana and banana vs. pineapples having statistically significant differences (p-values < 0.05). The results further reveal that the application of fly attractant can significantly reduce the influence of initial material characteristics on maggot production.

3.4. Waste Reduction Analysis

In general, the relative dry weight reduction in the trials varied from 52.5% to 82.4% (Figure 6). As previously observed, the application of fly attractant increased the number of maggots that affected the weight after harvesting; the amount of the remaining waste after harvesting was also observed to correspond to the number of maggots in a breeding vat. Breeding vats with more maggots ended up with a little amount of waste remaining. In this study, the highest waste reduction was achieved from the combination of 8 days and banana waste materials with a waste reduction efficiency of 82.4%. In the literature, maggots have also been observed to be highly efficient in organic waste reduction [46].

One of the interesting phenomena was that during the experiments, it was observed that after some time the cultivation vats were generating a considerable amount of liquid that in turn created anaerobic and foul-smelling conditions. Those places with accumulated liquid were observed to be unsuitable for maggots as none of the maggots were observed in those places. In such situations, it is always important to design cultivation vats with some drainage provision to avoid an accumulation of liquid that would affect the productivity of the system.

4. Conclusions

The potential of recovering food waste through maggot production has been investigated, including the impact of fly attractant on the general performance of maggot production. From the results, it was observed that the application of fly attractant to the substrates had a significant influence on improving maggot weight. For instance, the mean maggot weight from the starch materials increased to approximately 119.54% with the application of fly attractant compared to the mean value obtained from the maggot weight without applying the fly attractant. Based on the correlation analysis, the number of days before harvesting and the average maggot weight had a very high correlation, with a correlation score of 0.96 (without fly attractant) and 0.87 (with fly attractant). However, as previously highlighted, the unpredictable changes in pH led to a moderate correlation between the pH and the average maggot weight, with a correlation index of 0.66 (without fly attractant) and 0.48 (with fly attractant). Furthermore, it was shown that applying a fly attractant significantly improved maggot yield. On the eighth day, for example, the banana materials produced up to 94 g/kg of maggot weight, a 32.4% increase over the identical material without a fly attractant. The relative dry weight loss in the trials, on the other hand, ranged from 52.5% to 82.4%. That is to say, in 1 kg of food waste material, approximately 0.525 kg to 0.824 kg was consumed during the maggot production process. The results of this study also showed that maggot production (especially when combined with the use of a fly attractant) can be an effective way to recover food waste. The leftovers from the maggot generation process, on the other hand, can be used as an organic fertilizer. Future research in this area could look into the possibility of maggot production waste as an organic manure for plant growth.