Holometabolous insects, as a striking group within the insect world, have attracted the attention of numerous biologists and ecologists due to their unique life cycles and morphological transformations. In nature, insects are an incredibly rich and diverse biological group, with their diversity manifested in various forms, lifestyles, and diets. Diet is a key concept in insect ecology, not only affecting the survival and reproduction of individual insects but also directly influencing the stability and balance of entire ecosystems.

This review will explore the dietary diversity of holometabolous insects and the construction of food networks related to them. Through in-depth research into the dietary adaptations and food choices of insects at different life stages, we can gain a better understanding of their roles and positions within ecosystems. Food networks, as complex interrelation webs in ecosystems, involve various ecological interactions such as predation and prey, competition, and mutualism, and are of significant importance in maintaining ecological balance.

Examining the dietary characteristics of holometabolous insects at different life stages allows for the analysis of their roles and impacts within food networks. Additionally, exploring methods for constructing food networks and how to use these methods to study insect dietary adaptations and ecological interactions is important. Furthermore, attention is drawn to the influence of human activities on the stability of food networks, and a call is made for enhanced conservation measures to preserve ecological balance and biodiversity.

By delving into the dietary diversity of holometabolous insects and the construction of food networks, a better understanding of the intricate relationships among different organisms in ecosystems can be achieved. This provides a scientific basis for the protection of biodiversity, the maintenance of ecological balance, and sustainable development. This review aims to offer new perspectives and insights into the field of insect ecology, fostering a deeper understanding of holometabolous insects and their roles within ecosystems.

1 The Life Cycle and Morphological Changes of Holometabolous Insects

Complete metamorphosis is a special life cycle form in insects, during which they go through several distinct stages of development, resulting in significant morphological changes. This lifecycle pattern is widespread in the insect world and has profound implications for insect dietary adaptations and survival strategies.

1.1 Definition and characteristics of complete metamorphosis

Complete metamorphosis is a form of insect life cycle, contrasting with incomplete metamorphosis. Its primary characteristic is the significant differences in morphology, ecological niche, and behavior between the larval and adult stages of insects. This difference to some extent reduces competition between larvae and adults, contributing to the stability of populations and the maintenance of ecological balance. Typically, complete metamorphic insects have a pupal stage or a similar inactive phase that separates the larval and adult stages, facilitating a smooth transition in morphology.

1.2 Different life stages of holometabolous insects

The life cycle of holometabolous insects consists of four stages: egg, larva, pupa, and adult. The egg is the initial developmental stage of insects and comes in various sizes, shapes, and colors. Eggs are typically deposited inside or outside suitable host organisms. The larval stage is the growth phase in the insect's life cycle. During this stage, insects undergo significant changes in size and external characteristics as they grow through feeding and molting. The pupal stage is the most dramatic phase of morphological change. In this stage, insects undergo significant tissue reconstruction and transform into the appearance of an adult. The adult stage is the reproductive and perpetuation phase of insects and is characterized by mature reproductive organs and specific lifestyles.

1.3 The impact of morphological changes on dietary adaptation

The morphological changes in holometabolous insects have a significant impact on their dietary adaptation. The distinct differences in morphology between larvae and adults often result in different abilities in food selection and utilization. Larvae typically have a strong feeding capacity to meet their rapid growth requirements, while adults are more focused on reproduction and finding suitable breeding sites. For example, butterfly larvae are herbivorous (Figure 1), relying on a substantial intake of food to support their rapid growth, while adults primarily feed on nectar to obtain enough energy for reproduction.

The morphological changes during the pupal stage also provide opportunities for dietary adaptation in insects. During the pupal process, there are significant alterations in the insect's body tissues, including adjustments to the digestive system and mouthparts. These changes enable adults to better adapt to various food sources. Take cockroaches as an example; there is a noticeable difference in mouthpart structure between their larvae and adults. Larvae have more adaptable chewing mouthparts, while adults have more versatile mouthparts that can accommodate different types of food, such as liquids and solids.

In conclusion, the life cycle and morphological changes of holometabolous insects have far-reaching effects on their dietary adaptations. The morphological characteristics and behaviors at different stages enable insects to efficiently acquire food resources in diverse environments, thereby sustaining the survival and reproduction of their populations. The existence of this lifecycle pattern provides a crucial biological foundation for the success of insects in complex and ever-changing ecological environments.

2 Insect Dietary Adaptation and Diversity

Insects, as one of the largest populations on Earth, exhibit remarkable features in terms of dietary adaptation and diversity. Within ecosystems, insects, with their diverse diets, form intricate and complex food networks, making significant contributions to the maintenance of ecological balance and biodiversity (Barbour et al., 2016).

2.1 Types and classification of insect diets

The types and classification of insect diets are diverse and can be categorized as herbivorous, carnivorous, detritivorous, parasitic, etc. (Blüthgen et al., 2003). Herbivorous insects primarily feed on plants and have adaptations for digesting and utilizing various plant parts. Some herbivorous insects, when consuming plants, choose specific plant parts such as leaves, stems, or fruits to obtain maximum nutritional value. In contrast, carnivorous insects prey on other animals, including insects and spiders. They typically possess sharp mouthparts and rapid mobility to capture and digest their prey.

2.2 Reasons for insect dietary adaptation

The reasons for insect dietary adaptation are complex and diverse, with one key driving factor being niche differentiation. In the same ecological environment, different species of insects reduce direct competition among themselves by differentiating in terms of food sources, timing, and spatial distribution. This enables them to effectively utilize limited resources while coexisting. This differentiation results in diversity in food selection and utilization among different insects.

Furthermore, competition for resource utilization is also a significant driving factor for insect dietary adaptation. Insects rely on food resources for their survival and reproduction, and the scarcity of resources prompts insects to differentiate in their food choices, thereby avoiding excessive competition. The dietary differences among different insect species can alleviate resource competition within the same species, leading to diverse food utilization strategies within ecosystems.

2.3 Dietary adaptation cases in different insect species

There are a wide variety of dietary adaptation cases in different insect species, showcasing the remarkable ingenuity of insects in food selection and utilization. For instance, ants are a typical example of insects that exhibit dietary adaptation through division of labor. Ant colonies consist of different individuals, with some responsible for foraging for food (Figure 2), some guarding the nest, and some involved in reproduction. This division of labor allows ant colonies to efficiently acquire food, protect their nests, and thus survive and reproduce in complex ecological environments.

Another example is butterflies in the family Lepidoptera, which exhibit dietary adaptation through symbiotic relationships with plants (Figure 3). Butterflies, with their long proboscis and specialized tongue structures, can effectively extract nectar from flowers, while also serving as pollinators for plants during the process (Carreck and Williams, 2002). This mutualistic relationship not only meets the nutritional needs of butterflies but also promotes the reproduction and dispersal of plants.

In conclusion, insect dietary adaptation and diversity play an indispensable role in ecosystems. Through different food selection and utilization strategies, insects create intricate interactions within food networks, contributing to the maintenance of ecological balance and diversity. Understanding dietary adaptation cases in different insect species helps to gain a deeper understanding of the mechanisms behind biodiversity formation, providing crucial scientific foundations for ecological conservation and sustainable development.

3 Concept and Construction of Food Networks

As one of the central concepts in ecology (mclean et al., 2016), food networks reveal the interactions and relationships among biological populations. Constructing food networks helps to gain a deeper understanding of the structure and functioning of ecosystems, as well as the roles and positions of different organisms within them. Particularly, holometabolous Insects, as members of food networks, have a significant impact on the formation and maintenance of these networks due to their unique life cycles and dietary adaptations (Schoenly et al., 1991).

3.1 Definition and components of food networks

A food network is composed of a series of biological populations interconnected through food chains and food webs. A food chain represents a linear relationship describing how one organism in the chain preys on another (Li et al., 1996). On the other hand, a food web is more complex and reflects the intricate interactions among multiple biological populations within an ecosystem. Biological populations in a food network typically include plants, herbivorous insects, carnivorous insects, predators, carnivorous animals, and various other types, all linked together through trophic relationships, collectively shaping the structure of the ecosystem.

3.2 Methods for constructing food networks

Constructing a food network is a complex and systematic process that involves various research methods (van Veen et al., 2006). One of these methods is dietary analysis, which involves observing and recording the feeding behavior of organisms to understand their food sources and dietary types. Field observations are also a crucial means of building food networks, as researchers can gather information on trophic relationships among different biological populations through field surveys and observations. Additionally, data modeling methods play a significant role in constructing food networks. Researchers can utilize mathematical models and computer simulations to simulate food interactions among different organisms in an ecosystem and predict the structure of food chains and food webs.

3.3 The unique role of holometabolous insects in food networks

Holometabolous insects hold a distinct position and role within food networks. Due to their experience of multiple ecological stages throughout their life cycle, holometabolous insects can acquire food resources in different ecological niches (Sanders et al., 2018). For instance, the larval stage of an insect may be herbivorous, while the adult stage may be pollen-feeding, occupying different trophic levels within the food network. This diverse dietary adaptation gives holometabolous insects a higher degree of flexibility within food networks, enabling them to adapt to various environments and resource fluctuations. Additionally, the morphological changes in holometabolous insects offer opportunities for the formation of food networks. During their larval and adult stages, these insects may have different dietary requirements for various food resources, leading to the establishment of complex and diverse trophic relationships.

Food networks are intricate and complex networks of interactions within ecosystems, revealing the relationships among biological populations. Constructing food networks necessitates the integrated use of various research methods to gain a better understanding of the structure and functioning of ecosystems. Holometabolous insects, as members of food networks, contribute beneficial insights to the formation and maintenance of these networks through their unique life cycles and dietary adaptations, enriching our understanding of ecological interactions.

4 The Role of Holometabolous Insects in Food Networks

Holometabolous insects, as essential components of ecosystems, play diverse roles in food networks. They not only serve as predators and prey within these networks but also influence the structure and ecological balance of food chains and food webs. Their unique life cycles and dietary adaptations grant them multiple positions within food networks.

4.1 Different roles of holometabolous insects as predators and prey

Holometabolous insects may play different roles as predators and prey at different stages of their life cycle. During the larval stage, some holometabolous insects may exhibit predatory behavior by preying on other insects, small animals, or plants. For example, antlion larvae prey on ants by ambushing them in pit traps to fulfill their nutritional requirements. However, during the adult stage, holometabolous insects may feed on plant resources like nectar and fruits, making them prey within the food network. This change in roles across different life cycle stages results in complex ecological roles for holometabolous insects within food networks.

4.2 Position in food chains and food webs, and their impact on ecological balance

In food networks, food chains and food webs are crucial ways of organizing the relationships between biological populations. Holometabolous insects hold a unique position within them. In food chains, holometabolous insects typically serve as intermediate links, transferring energy and nutrients from lower-level organisms to top-level carnivores. This intermediary role helps maintain the stability of the food chain, ensuring the transfer of energy and matter.

In more complex food webs, the roles of holometabolous insects become even more diversified. Through interactions with other biological populations, they contribute to the creation of intricately interconnected food relationship networks, influencing the overall balance of the entire ecosystem. The dietary adaptations and life cycle changes of holometabolous insects provide diversity and flexibility to the structure of food networks, enhancing the ecosystem's resilience against external pressures and changes.

Many case studies have supported the significant role of holometabolous insects in food networks (Holmes et al., 2020). For example, butterfly larvae feed on plants, while adults feed on nectar, forming a mutualistic relationship with plants through this dietary adaptation. This mutualistic relationship not only affects the survival and reproduction of butterflies but also has a positive impact on pollination and reproduction in plants.

Another example is the interaction between ants and bees. Ant lion larvae prey on ants, thus affecting the population and distribution of ants. On the other hand, bees contribute to plant reproduction as pollinators. The interactions between these two species constitute a complex food web, exerting both direct and indirect impacts on ecological balance.

Holometabolous insects play various roles in food webs, acting as both predators and prey. Their life cycles and dietary adaptations have significant impacts on the structure and stability of food chains and food webs. Through diverse case studies, a deeper understanding of the role of insects in food networks can be gained, providing a scientific basis for ecosystem conservation and management.

5 The Stability and Threats to Food Networks

The stability of food networks is a critical attribute of ecosystems, affecting the population and distribution of biological species, as well as the overall functionality of the ecosystem. However, the activities of modern society are posing significant threats to food networks, especially for holometabolous insects within them. Their vulnerability demands attention and protection.

5.1 Discussing the concept of food network stability, including resilience and robustness

The stability of a food network refers to its ability to maintain its normal structure and functionality when faced with external pressures or disturbances. Resilience is an essential attribute of food networks, indicating the system's capacity to quickly return to a stable state after being disrupted. Robustness, on the other hand, denotes the system's ability to maintain its structure and functionality in the face of disturbances. A stable food network should possess sufficient resilience and robustness to withstand various environmental changes and disturbances.

5.2 Analyzing the impact of human activities on food networks, such as habitat destruction and climate change

The impact of human activities on food networks is becoming increasingly evident, particularly due to factors like habitat destruction and climate change. Habitat destruction has led to the loss or fragmentation of habitats for many species, putting insect populations at risk of losing their food sources and breeding sites. Climate change has also altered temperature and precipitation patterns in ecosystems, affecting the growth, reproduction, and migration of insects. These changes have a direct impact on the structure and functionality of food networks, potentially leading to disruptions in ecological balance.

5.3 Exploring the vulnerability and conservation needs of holometabolous insects in food networks

Within food networks, holometabolous insects may exhibit vulnerability due to their unique life cycles and dietary adaptations. Their ecological roles and dietary adaptations at different stages can make them more sensitive to environmental changes. For instance, the larval stage may rely on specific food sources, and the loss of these resources could threaten larval survival. Morphological changes and food choices during the pupal and adult stages may also render them susceptible to factors like climate change.

In order to protect holometabolous insects and the stability of the entire food network, implementing a series of conservation measures becomes particularly crucial. Firstly, safeguarding the habitats of these insects is paramount. This can be achieved by reducing habitat destruction and preserving natural environments to provide a stable living environment for insects. Secondly, enhancing climate change adaptation and mitigation measures can help reduce the impact of environmental changes on food networks. Additionally, conducting scientific research to gain a deeper understanding of the ecological characteristics and roles of holometabolous Insects can aid in developing more targeted conservation strategies.

In summary, the stability of food networks is influenced by various factors, and human activities are a significant contributor to the threats facing these networks. Holometabolous insects, as important components of food networks, require adequate attention due to their vulnerability. Protecting holometabolous insects is not only necessary for maintaining ecological balance but also a crucial element in preserving biodiversity and ecological health. By implementing comprehensive conservation measures, we can better safeguard the stability of food networks and ensure the sustainable development of ecosystems.

6 Future Prospects and Research Directions

As human society continues to evolve, research on food networks and ecosystems becomes increasingly crucial. Future studies should not only focus on the structure and functionality of food networks but should also pay special attention to holometabolous insects within them. Exploring their dietary adaptations, ecological roles, and how to protect this vital ecological component will be essential areas of research in the coming years.

In the future, research on food networks will place a greater emphasis on systematics and comprehensiveness. Researchers will employ advanced techniques such as gene sequencing and ecological modeling to delve deeper into the interactions and impacts among various organisms within food networks. Additionally, interdisciplinary collaboration is expected to be a trend in future research, with the fusion of fields like ecology, biology, computer science, and more, contributing to a more holistic understanding of the complexity of food networks. Future studies can further explore the dietary adaptations and roles of holometabolous insects. Through detailed investigations into the dietary choices, food sources, and food relationships of different insect species, specific roles and impacts of various insects within food networks can be revealed. Simultaneously, ecological modeling and field observations can be used to investigate the intricate food network relationships of insects, shedding light on their influence on ecological balance and ecosystem functionality.

In future research, there is a growing need to emphasize the importance of protecting holometabolous insects and the entire food network. Maintaining ecological balance and biodiversity is crucial for the stability of the Earth's ecosystems, and the threats posed by human activities are becoming increasingly severe. Therefore, it is essential to strengthen conservation measures, reduce habitat destruction, and control climate change to protect ecosystem stability and the survival of holometabolous insects. In terms of conservation, governments, research institutions, and society as a whole must collaborate to develop and implement effective conservation policies. Furthermore, environmental awareness among the public needs to be raised, and each individual can contribute to protecting food networks and ecological balance by making environmentally conscious choices in their daily lives, thereby reducing adverse impacts on ecosystems.

In conclusion, future research on food networks will make greater strides in systematics and comprehensiveness. Further investigating the dietary preferences and food network relationships of holometabolous insects will aid in a deeper understanding of their role within ecosystems. Simultaneously, it is imperative to strengthen conservation measures to protect holometabolous insects and their associated food networks, thereby safeguarding the stability of ecological balance and biodiversity. This necessitates collective efforts from global society to create a more favorable environment for the future of ecological health and sustainable development.

Author’s contributions

GTX was responsible for reviewing, organizing, and writing the relevant literature materials for the initial draft of this review, participated in discussions, and contributed to the paper's revisions. GTX is the lead author of this review, responsible for both the writing and revision of the paper. Author have read and approved the final manuscript.

Acknowledgments

I would like to express my gratitude to Ms. Liu Chuchu for her guidance during the writing process of this review and for providing detailed feedback on my manuscript. The illustrations used in this review were sourced from the internet. If there are any concerns about rights or the need for usage permissions, please contact the author to ensure that rights are respected. Thank you for your understanding and support.

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