There are various symbiotic relationships in nature, including mutualism, parasitism, predation, and so on. Among them, reciprocal symbiosis refers to the relationship between two or more species that benefits from mutual cooperation. The mutually beneficial relationship between ants and aphids is a typical example.

Aphids are insects that feed on plant sap, but they cannot fully digest the sugar in plant sap, so they need to secrete excess honeydew into nectar for discharge. However, ants can use honeydew as food while protecting aphids from natural enemies. This mutually beneficial relationship not only benefits ants and aphids themselves, but also plays an important role in the balance and stability of the entire ecosystem.

This study will explore the mechanism and ecological significance of the mutually beneficial relationship between ants and aphids from the perspectives of biology and biochemistry, and look forward to future research directions. By studying this symbiotic relationship in depth, we can gain a deeper understanding of the interactions between organisms in nature, providing new ideas and methods for ecological protection and resource utilization (Oliver and Leather, 2008).

1 Biological Characteristics of Ants and Aphids

Ants and aphids are common insects that share some similarities and differences in their biological characteristics.

1.1 Characteristics of ants

Ants are a kind of social insect, usually living in groups (Figure 1; Figure 2). They have the following characteristics (Hölldobler and Wilson, 1990; Rosengaus and Traniello, 1993): the body is divided into three parts: the head, chest, and abdomen, with six legs and a pair of antennae. The body presents different shapes and sizes, and is divided into worker ants, soldier ants, male ants, and female ants according to their roles and responsibilities. Ants have a wide range of feeding habits, including eating plants, animals, decaying corpses, etc. They can also obtain nutrients by collecting sweet substances such as nectar and nectar. Ants have a high degree of sociality, and members within a group communicate and collaborate through chemical signals, such as information transmission, task allocation, and reproductive control (Pierce et al., 2002).

1.2 Characteristics of aphids

Aphids are a type of small soft insects that mainly live on plants and feed on plant sap (Figure 3; Figure 4). They have the following characteristics: their bodies are oval or oval shaped, usually in colors such as green, yellow, or brown, with six legs and a pair of antennae. Aphids have mouthparts and can feed by sucking on plant juices. Aphids have strong reproductive capacity, and can reproduce through asexual reproduction and sexual reproduction. Aphids are divided into two types: winged and wingless. Winged aphids can migrate, while wingless aphids usually settle on plants.

1.3 Relationship between ants and aphids

There is a mutually beneficial relationship between ants and aphids (Figure 5), where ants can provide protection and food, while aphids can provide sweet substances and nutrients for ants (Price, 1991).

Aphids can secrete a substance called honeydew, which is a liquid rich in sugar and amino acids. Ants can obtain nutrients by collecting honeydew. At the same time, the secretions of aphids can also provide nutrients for other insects, such as ants bringing the honeydew back to their nests for other members to eat.

The protective effect of ants on aphids is also crucial (Kost and Heil, 2006). Aphids usually settle on plants, they are easily attacked by natural enemies, while ants can protect aphids by patrolling and attacking them. In addition, ants also bring aphids back to their nests, providing them with a warm and safe living environment.

Overall, the relationship between ants and aphids is a typical symbiotic relationship, where both parties achieve mutual benefit by providing protection and nutrition to each other. This relationship is very common in nature and plays an important role in maintaining the balance and stability of ecosystems (Rudgers and Strauss, 2014).

2 The Contribution of Aphids to Ants

Aphids are small herbivorous insects that feed on plant sap and secrete a sweet liquid called honeydew. This honeydew is quite important for ants because it can provide nutrients and energy for them. In addition, aphids can also attract ants to protect themselves, providing them with protection opportunities (Wang and Li, 2013; Zhang and Wei, 2017).

2.1 The importance of honeydew to ants

The honeydew secreted by aphids is a sweet liquid containing a large amount of sugar and amino acids (Wäckers et al., 2007) (Figure 6). Ants can obtain nutrients and energy by licking honeydew, which is crucial for their survival and reproduction. Research has shown that ants can improve their survival rate and reproductive ability by licking nectar. In addition, honey dew can also provide ants with water and minerals to meet their basic physiological needs.

2.2 How aphids attract ants to protect themselves

Aphids can attract ants to protect themselves by secreting a sweet liquid called honeydew. Aphids usually secrete honeydew on the leaves and stems of plants, so that they can easily find honeydew and establish their own nests nearby.

When aphids are attacked by natural enemies, they will send warning signals to nearby ants by waving their antennae and legs (Raine and Chittka, 2008). These signals can let ants know that aphids are under attack and require ant protection. Ants will immediately go to the location of aphids and use their antennae and legs to drive away their natural enemies.

In addition, aphids also secrete a substance called "aphid milk", which can provide ants with additional nutrients and energy. Ants can obtain these nutrients and energy by licking aphid milk, thereby enhancing their survival and reproductive ability.

In general, the contribution of aphids to ants is mainly reflected in two aspects: firstly, they secrete honeydew to provide nutrients and energy for ants; and secondly, they attract ants to protect themselves by secreting aphid milk and issuing warning signals. This mutually beneficial relationship not only helps ants and aphids survive in nature, but also plays an important role in maintaining the balance and stability of ecosystems.

3 The Contribution of Ants to Aphids

The mutually beneficial relationship between ants and aphids (Sánchez-Peña and Hernández-Fuentes, 2017) not only involves aphids providing honeydew and aphid milk to ants, but also provides a lot of help to aphids. The contribution of ants to aphids will be introduced from two aspects (Li, 2018).

3.1 Protection

The protection of aphids by ants is one of the most obvious aspects of the mutually beneficial relationship (Figure 7). Aphids use a lot of nutrients and energy when producing honeydew. As a result, they are often weak and easy to be attacked by natural enemies. To protect the aphids, ants set up nests near the aphids and send worker ants to patrol them. As soon as a predator is detected, the worker ants will send out a warning signal to direct other ants to come to their aid. In addition, the ants will take the aphids inside the nest to keep them out of danger.

3.2 Help to reproduce

In addition to protecting aphids, ants also help the reproduction of aphids. Aphids are wingless insects that rely on either asexual or sexual reproduction. In asexual reproduction, aphids produce a group of identical offspring by reproducing as a single female. In this process, ants help aphids find suitable breeding sites and help them spread. In sexual reproduction, aphids need to find a suitable partner to mate with. Ants will help aphids find a partner and provide protection during mating and egg laying.

Overall, ants contribute to aphids both in terms of protection and in helping reproduction. This mutually beneficial relationship not only helps aphids and ants survive in nature, but also plays an important role in maintaining the balance and stability of the ecosystem.

4 Biochemical Mechanisms

4.1 Biochemical mechanisms of honeydew secretion by aphids

The biochemical mechanism of honeydew secretion by aphids is a complex process involving many biochemical reactions and molecular signaling pathways (Lange and Egan, 2019). When aphids feed on plant sap, they secrete excess sugar through special glands to form honeydew outside the body. The main components of honeydew are glucose and fructose, and it also contains some amino acids, organic acids and minerals. All these components are products that aphids absorb from the plant and excrete after metabolism.

The metabolic process in aphids involves the participation of several enzymes (Stadler, 2001), the most important of which are glucose-6-phosphate dehydrogenase (G6PDH) and fructose-6-phosphate dehydrogenase (F6PDH). These two enzymes are involved in the metabolic processes of glucose and fructose, respectively, converting them into energy and other metabolites. Also, aphids secrete a number of enzymes, such as galacturonase, glucose oxidase and peroxidase, which help to break down and metabolize sugars and other organic substances in plant sap.

In addition to metabolic processes, the secretory system in aphids also plays an important role in the production of honeydew. The glands that secrete honeydew in aphids are called honey glands, located in the abdomen of the aphid. The honey gland contains a large number of endoplasmic reticulum and Golgi apparatus, organelles that convert metabolites from the aphid's body into honeydew and secrete it outside the body. Besides, aphids secrete a number of hormones and signaling molecules, such as abscisic acid, gibberellin and ethylene, which regulate the secretory activity of the nectaries.

4.2 Exploring how ants recognize honeydew

Ants can recognize honeydew by a variety of means, including smell and touch (Figure 8). Honeydew secreted by aphids contains many volatile compounds and odorous substances that can be perceived by the olfactory organs of ants. The olfactory organ of ants is located on the antennae of the head and consists of many sensory cells and neurons. When ants approach the honeydew, their olfactory organs are stimulated by the compounds in the honeydew and produce corresponding nerve signals to tell the ants the presence of honeydew.

In addition to smell, ants can recognize honeydew by touch. Honeydew usually drips onto leaves or other objects, forming small droplets. When ants come in contact with these droplets, their tentacles sense characteristics such as the consistency and temperature of the droplets to determine if this is honeydew. Furthermore, ants can also find honeydew by touching the body surface of aphids, which usually leave some traces of honeydew on the body surface.

Overall, ants can identify honeydew by a variety of means, including smell and touch, and this ability to identify plays a crucial role in their mutually beneficial relationship with aphids.

5 Ecological Significance

The reciprocal and mutually beneficial relationship between ants and aphids is important for the ecosystem (Davidson and McKey, 1993; McFrederick et al., 2013; Hong and An, 2016). First, aphids are a major food source for many insects and birds. Therefore, the population and distribution of aphids have an important impact on the stability of the whole ecosystem. And ants help to maintain the population and distribution of aphids through a mutually beneficial relationship with aphids, thus protecting the stability of the whole ecosystem (Zhao and Zhao, 2009).

Second, aphids secrete a sweet liquid called honeydew when they feed on plant sap, which is also an important food source for many insects and birds. By seeking out and protecting aphids, ants have access to this sweet sap as a food source for themselves. This mutually beneficial relationship not only helps ants and aphids, but also provides a rich food resource for the entire ecosystem.

In addition, the mutually beneficial relationship between ants and aphids helps plants to grow and reproduce. When aphids feed on plant sap, they secrete substances that promote plant growth and reproduction. And by protecting the aphids, the ants can promote the distribution of the aphids on the plant, thus increasing the chances that the plant will benefit.

By taking advantage of the mutually beneficial relationship between ants and aphids, we can take some measures to protect the ecosystem. First, we can promote this mutually beneficial relationship by protecting aphid habitat and increasing the number of ants. Second, we can reduce the impact on aphids by controlling the amount of pesticides used and changing agricultural practices to protect the stability of the entire ecosystem.

In conclusion, the mutually beneficial relationship between ants and aphids is very important to the ecosystem, and their interactions not only help themselves but also provide a rich resource for the entire ecosystem. By grasping the ecological significance of this relationship, we can take measures to protect the ecological environment and achieve sustainable development of the ecosystem.

6 Conclusion

Taking the above analysis together, we can conclude that the mutually beneficial relationship between ants and aphids plays a crucial role in the stability of the ecosystem and the conservation of the ecological environment (Lanan and Bronstein, 2013). Aphids are an important food source for ants, while ants maintain the balance of the ecosystem by protecting aphids to obtain sweet honeydew and also controlling the aphid population.

From a biological point of view, this mutually beneficial relationship is due to evolutionary adaptations between ants and aphids. Aphids attract ants by secreting honeydew, while ants protect aphids to obtain honeydew and control aphid populations. From a biochemical point of view, this mutually beneficial relationship is due to the fact that the honeydew secreted by aphids is rich in carbohydrates and amino acids, which provide ants with the nutrients they need and also promote plant growth and reproduction.

Future research can be conducted in the following aspects: First, the evolutionary adaptation mechanism between ants and aphids can be further studied to explore the role and significance of this mutually beneficial relationship in the evolutionary process; Second, the chemical composition of the honeydew secreted by aphids can be studied in depth to explore the effects of it on the nutrition and growth of ants and plants; Finally, we can study how to use this mutually beneficial relationship to protect the ecological environment and explore how to maintain the balance of the ecosystem by controlling the aphid population and regulating the relationship between ants and aphids.

In conclusion, the mutually beneficial relationship between ants and aphids is an important biological phenomenon in the ecosystem, which not only helps the ants and aphids themselves but also provides rich resources for the whole ecosystem. By studying this relationship in depth, we can better understand the operation mechanism of the ecosystem and provide scientific basis for the conservation and sustainable development of the ecological environment.

Authors’ contribution

GTX and XJ were the leaders of this project, conceiving the thesis, writing draft, revising and finalizing the manuscript; ZJ and ZJY were involved in the collection and organization of the materials. All authors read and approved the final manuscript.

Acknowledgement

This study was funded by the Research and Scientific Research Fund of Cuixi Academy of Biotechnology.

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