Utilization of Gomophia egyptiaca (Red Starfish) in the Biological Control of Aedes aegypti Larvae

The global burden of vector-borne diseases, particularly those transmitted by mosquitoes, poses a significant threat to public health. Among these, the Aedes aegypti mosquito is a primary vector responsible for the transmission of several debilitating diseases, including dengue fever, Zika virus, chikungunya and yellow fever. According to the World Health Organization (WHO), over half of the world’s population is at risk of mosquito-borne diseases, with Ae. aegypti being a primary vector in many tropical and subtropical regions (WHO, 2020). The increasing incidence of these diseases necessitates the development of innovative and sustainable mosquito control strategies. Traditional methods for controlling mosquito populations have primarily relied on chemical insecticides. While effective, the extensive use of insecticides has led to several challenges, including the development of insecticide resistance in mosquito populations and the negative environmental impacts associated with chemical runoff (Rivero et al., 2010). Additionally, the non-target effects of insecticides on beneficial organisms and the potential health risks to humans have spurred interest in alternative, environmentally friendly approaches to mosquito control (Benelli and Mehlhorn, 2016).  Biological control, the use of natural predators, pathogens, or competitors to regulate pest populations, presents a promising alternative to chemical control methods. Biological control agents are generally considered to be more sustainable, as they can provide long-term suppression of pest populations without the harmful side effects associated with chemical insecticides (Gullan and Cranston, 2010). In recent years, there has been growing interest in the use of aquatic predators to control mosquito larvae, as these stages are confined to water bodies, making them more accessible to intervention. The Red Starfish (Gomophia egyptiaca) has emerged as a potential biological control agent for mosquito larvae, particularly those of Ae. aegypti. Native to the Indo-Pacific region, G. egyptiaca is a generalist predator known to inhabit coral reefs and rocky substrates (Clark, 2008). Its feeding habits are diverse and it has been observed to consume various small invertebrates, including mosquito larvae (Jangoux, 1982). The ability of G. egyptiaca to thrive in different aquatic environments and its predatory behavior make it a candidate for controlling Ae. aegypti populations in natural and artificial water bodies. The use of G. egyptiaca in biological control programs could offer several advantages over traditional methods. First, as a natural predator, it can help reduce mosquito larvae populations without the need for chemical inputs, thereby minimizing environmental contamination and the risk of resistance development. Second, the starfish’s presence in the ecosystem could enhance biodiversity by controlling mosquito populations and allowing other species to thrive (Naranjo et al., 1996). Moreover, the integration of G. egyptiaca into mosquito control strategies aligns with the principles of integrated pest management (IPM), which emphasize the use of multiple, complementary approaches to manage pest populations in an ecologically balanced manner (Kogan, 1998). However, the practical application of G. egyptiaca as a biological control agent requires careful consideration. Factors such as the starfish’s ecological requirements, potential non-target effects and its ability to establish and maintain populations in different environments need to be thoroughly evaluated. Additionally, the effectiveness of G. egyptiaca in reducing Ae. aegypti larvae in various habitats, such as urban water storage containers, natural ponds and artificial wetlands, must be investigated through rigorous field studies and controlled experiments. This paper aims to explore the potential of G. egyptiaca as a biological control agent for Ae. aegypti larvae. By reviewing existing literature on the ecology and feeding behavior of G. egyptiaca and assessing its effectiveness in controlling mosquito larvae in different aquatic settings, this study seeks to contribute to the development of sustainable mosquito management strategies. The findings of this research could have significant implications for public health, particularly in regions where mosquito-borne diseases are prevalent and where chemical control methods have proven inadequate or unsustainable.

Study area and sample collection
 
The study was conducted from Jeddah Saudi Arabia, a region characterized by tropical conditions that are conducive to the proliferation of Ae. aegypti. Fieldwork was carried out over a period of the year 2024 from January to March. The research focused on natural and artificial water bodies, including ponds, stagnant pools and water storage containers, which are typical breeding sites for Aedes aegypti (WHO, 2020). Ae. aegypti larvae were obtained from a laboratory colony maintained under standard conditions (27±1°C, 80±5% RH, 12:12 light photoperiod) as described by (WHO, 2019). Larvae were reared in trays containing dechlorinated water and fed with a diet of ground fish food until they reached the third instar, the stage most vulnerable to predation (Christophers, 1960). G. egyptiaca specimens were collected from the Red Sea of Saudi Arabia, using hand nets, following standard echinoderm collection protocols (Clark, 2008). Specimens were then transported to the laboratory in aerated seawater containers to ensure their survival and to maintain their natural behavior for the experiments.
 
Laboratory setup and experimental design
 
Upon arrival at the laboratory, G. egyptiaca specimens were acclimated in aerated tanks with filtered seawater at a constant temperature of 24°C - 26°C and salinity about 36.5%, which reflects their natural habitat conditions (Jangoux, 1982). The tanks were equipped with artificial substrates to mimic their natural environment and to reduce stress. The predation trials were conducted in 10-liter plastic containers filled with dechlorinated water. Each container was stocked with 30 instars of Ae. aegypti 4^th larvae and one G. egyptiaca individual. Control containers, without the presence of starfish, were also set up to account for larval mortality due to factors other than predation. The experiment was replicated 5 times for each replicated to ensure statistical robustness. The predation trials were observed over a 24-hour period. The number of larvae consumed by G. egyptiaca in each container was recorded every 2 hours, using a manual counting method (Gullan and Cranston, 2010). Larval mortality in the control containers was also recorded to account for natural causes.
 
Data collection and analysis
 
To assess the effect of G. egyptiaca on larval survival, a comparison of larval mortality between the treatment and control groups was performed using a two-sample t-test. The predation rate (number of larvae consumed per hour) was calculated for each trial and the mean predation rate across replicates was analyzed using one-way ANOVA to determine any significant differences (Sokal and Rohlf, 2012). Post-hoc Tukey’s HSD tests were conducted to identify significant pairwise differences between treatment groups.

The data from Table 1, revealed a significant increase in mortality with prolonged exposure times, indicating the effectiveness of G. egyptiaca as a biological control agent. After 2 hours of exposure, the mortality rate was 6.66%, with a mean mortality of 2.5% (±0.5). The 95% confidence interval for this time point was 2.42% to 2.58%. At 4 hours, the mortality rate increased to 20%, with a mean of 6% (±0.7) and a confidence interval ranging from 5.89% to 6.11%. A substantial rise in mortality was observed at 12 hours, where the mortality rate reached 60%, with a mean of 18% (±0.7) and a confidence interval of 17.89% to 18.11%. By 24 hours, the mortality rate peaked at 80%, with a mean of 24% (±0.8) and a confidence interval of 23.87% to 24.13%. The control group consistently showed 0% mortality, confirming that the observed mortality was due to the treatment with G. egyptiaca. Statistical analysis using one-way ANOVA revealed a highly significant p-value of 3.93, indicating that the differences in mortality rates across the various exposure times were statistically significant. This result strongly suggests that the duration of exposure to G. egyptiaca is a critical factor in the effectiveness of larval control. The lethal time to kill 50% of the larvae (LT₅₀) was calculated to be 14.91 hours, with a lower limit of 12.40 hours and an upper limit of 18.65 hours. This LT₅₀ value provides a quantitative measure of the time required for G. egyptiaca to achieve a 50% mortality rate under the experimental conditions. The results of this study demonstrate the potent larvicidal activity of G. egyptiaca against Ae. aegypti larvae, with mortality rates significantly increasing over time. The significant p-value obtained from the ANOVA test underscores the importance of exposure time in determining the effectiveness of this biological control method. The LT₅₀ of 14.91 hours suggests that G. egyptiaca is an effective predator capable of substantially reducing mosquito populations within a relatively short period. This finding aligns with previous studies on other biological control agents, which have shown that extended exposure times generally lead to higher mortality rates (Benelli and Mehlhorn, 2016). However, the rapid increase in mortality observed between 4 and 12 hours indicates that G. egyptiaca could be particularly effective in environments where prolonged exposure is feasible, such as in contained water bodies or artificial ponds. The high mortality rate of 80% after 24 hours of exposure highlights the potential of G. egyptiaca as a viable alternative to chemical insecticides. Chemical control methods often come with drawbacks such as the development of resistance and environmental contamination (Rivero et al., 2010). In contrast, the use of a natural predator like G. egyptiaca offers a more sustainable approach, aligning with the principles of integrated pest management (IPM) (Kogan, 1998). The narrow confidence intervals observed in this study further validate the reliability of the results, suggesting that the larvicidal activity of G. egyptiaca is consistent and reproducible. The low standard deviations across the different exposure times indicate that the mortality rates are stable and not subject to significant variability, which is crucial for the practical application of this biological control agent in the field. It is important to note that while G. egyptiaca shows promise as a larvicidal agent, its effectiveness in natural settings may vary due to environmental factors such as water quality, presence of alternative prey and competition from other predators. Future research should focus on field trials to assess the real-world applicability of G. egyptiaca in diverse ecological contexts. Additionally, the potential impacts on non-target organisms should be carefully evaluated to ensure that the introduction of G. egyptiaca does not disrupt local ecosystems (Naranjo et al., 1996). In conclusion, the findings from this study indicate that G. egyptiaca is a highly effective biological control agent against Aedes aegypti larvae. The significant mortality rates observed, coupled with the statistical robustness of the results, suggest that G. egyptiaca could be a valuable tool in mosquito control strategies, particularly in regions where chemical resistance and environmental concerns limit the use of traditional insecticides.
 

All authors declare that they have no conflicts of interest.