Survival Rate and Growth Performance of the Fighting Beetle (Xylotrupes socrates Schaufuss, 1864) in Mass Rearing at Different Stocking Densities

Abstract

Background and Objectives : The fighting beetle (Xylotrupes socrates) is a native insect species that plays an important role in the ecosystem by decomposing plant residues and enriching soil fertility. It also serves as a crucial component of the food chain, helping to maintain ecological balance. Recently, insect consumption has gained significant attention as an alternative source of protein due to its high nutritional value, safety for human health, and environmental sustainability. The fighting beetle has significant potential as a protein source for humans. Rearing this species by mimicking natural conditions is feasible and has often been practiced on an individual basis or under natural settings. However, to meet commercial demands and provide a sustainable protein supply, it is necessary to rear these beetles in large quantities. Stocking density is one of the key factors influencing the survival rates and growth performance of X. socrates.  However, there is no clear guideline on the optimal density for mass rearing. Therefore, this study aimed to investigate the survival and growth of the fighting beetle under four different rearing densities using a diet that mimics natural food sources. The findings will provide fundamental information for the development of large-scale rearing practices to produce safe and sustainable insect-based protein for human consumption.

Methodology : The fermented artificial diet for X. socrates larvae was formulated using rubber wood sawdust, dried cow manure, loamy soil, wheat flour and water. Fifty pairs of adult male and female beetles were used as breeding stock to produce first-instar larvae. Male and female adult beetles were fed with sugarcane for seven days before mating. Fertilized females were placed individually in 32-ounce plastic cups containing the prepared diet to promote oviposition. The first instar larvae were collected, pooled, and randomly assigned to four stocking densities: 25, 50, 75, and 100 larvae per container. The experiment followed a completely randomized design (CRD) with three replications per treatment. Larvae were reared in 230-liter plastic containers (90×120×37 cm) filled with 200 liters of substrate. The temperature of the substrate was measured weekly. The diet was replaced every month; during each replacement, larval weight and survival rate were recorded. Larvae were reared until they reached the reproductive adult stage. The number of adults emerging from each treatment was recorded to evaluate the effects of stocking density on survival performance. Data were analyzed to provide baseline information for mass-rearing practices.

Main Results : The results demonstrated that rearing density had a significant impact on larval growth performance and survival rate (p<0.05). At the beginning of the experiment, there were no statistically significant differences in the mean initial weights of larvae among the four treatments (p>0.05). By the third month (March), larvae reared at 50 individuals per container achieved the highest mean body weight. However, However, from the fourth to sixth months (April–June), the group reared at the lowest density of 25 individuals per container consistently exhibited the highest mean weight, with significant differences compared to the groups maintained at higher densities. This pattern persisted from the seventh to ninth months (July–September), confirming that lower rearing density favors greater weight gain. By the ninth month, which corresponds to the late third instar stage, larvae in the 25-larvae group reached a mean body weight of 23.02±0.49 g, whereas larvae in the highest density group of 100 individuals showed a mean of 19.18±1.35 g. The study also found that rearing density significantly affected larval survival rate (p<0.05). During the early phase of the experiment, all treatments maintained high survival rates above 90%, with no statistically significant differences observed (p>0.05). This suggests that initial rearing density does not affect short-term survival when food and space are still sufficient. However, as the rearing period progressed, the survival rates of the lower-density groups remained higher than those of the higher-density groups. By September, the 25-larvae group showed the highest mean survival rate at 52.00% for the larval stage and approximately 50.67% survival through to the reproductive adult stage. In contrast, the group reared at the highest density (100 larvae per container) exhibited a continuous decline in survival rate, with only 47.33% surviving at the late larval stage and 19.00% successfully developing to the reproductive adult stage.

Conclusions : Fighting beetles were successfully reared under group-rearing conditions using a diet that mimics natural conditions. However, stocking densities were found to be a critical factor influencing both growth performance and survival rate. The low-density treatment groups exhibited significantly higher mean body weight and survival rates compared to the high-density groups. These findings provide a basis for developing commercial-scale rearing systems. Further investigation into the causes of mortality during the third larval stage is an important issue and is recommended to enhance rearing efficiency and support the utilization of fighting beetles as a safe alternative protein source for human consumption.