Holometabolous insects are a group of insects that undergo complete metamorphosis, including four stages: egg, larva, pupa, and adult. These insects exhibit various unique behaviors and ecological characteristics, with their predation behavior being the most remarkable. The predatory behavior of holometabolous insects has significant implications for the balance of ecosystems and the sustainable development of agriculture.

There have been numerous studies and discoveries regarding the predation strategies and behavioral ecology of holometabolous insects. For instance, their methods of attack, capture, and localization are all related to their ecological environment and habitat adaptability. Moreover, the predatory behavior of holometabolous insects plays a significant role in controlling pest populations, influencing pest population structures, and maintaining the balance of ecosystems.

However, despite extensive research exploring the predation behavior of holometabolous insects, many unresolved issues remain in this field. For instance, there is a need for further research to quantitatively assess the ecological role of their predatory behavior in their ecosystems and to explore the practical applications of their predation strategies in agricultural production.

Therefore, this review aims to analyze and investigate the predation strategies and behavioral ecology of holometabolous insects. It will introduce the characteristics of their predatory behavior, analyze the adaptability and effects of their predation strategies, and explore the impact of their predatory behavior on their ecosystems. Additionally, this review aims to expand our understanding of holometabolous insects' predation behavior and promote its application in agricultural production and ecosystem conservation.

1 Characteristics and Ecological Role of Holometabolous Insects

1.1 Characteristics of holometabolous insects

Holometabolous insects have different forms and physiological characteristics in their four stages: egg, larva, pupa, and adult. Take butterflies as an example (Figure 1), the metamorphosis of holometabolous insects is more obvious compared to other insects. The eggs of holometabolous insects are relatively small and usually hatch into larvae. Larvae are typically the most active stage in the life cycle of holometabolous insects, and their food sources include plants, meat, carrion, and bees. Larvae have a completely different appearance, size, physiological characteristics, and lifestyle from adults. Pupae are the transitional stage between larvae and adults. They usually have a similar appearance to adults, but no wings and are in a dormant state. During the pupal stage, insects undergo significant changes in morphology and physiology, including organ differentiation and morphological adjustments. Adults are the final form of holometabolous insects, and their appearance is completely different from that of larvae and pupae. Adults usually have organs such as wings, compound eyes, and antennae, which are used for flying, foraging, and reproduction.

The characteristic of holometabolous insects are the obvious morphological and physiological changes that occur during their development. These changes enable them to adapt to different habitats and food sources, playing important roles in the ecosystem.

1.2 Ecological role of holometabolous insects

The ecological role of holometabolous insects involves multiple aspects within the ecosystem, including pest control, influencing pest population structures, promoting species diversity, nutrient cycling, and serving as a food source.

Holometabolous insects are an important component of natural enemies of insects in ecosystems. They control pest populations by preying on pests, thus maintaining the balance of the ecosystem. Their predatory behavior not only helps regulate pest populations but also influences pest population structures. For instance, certain holometabolous insects selectively prey on specific pest species, altering the proportion of the pest population. Moreover, the predation by holometabolous insects promotes species diversity, enriching the number and variety of species in the ecosystem. By preying on other insects and plants, and other organisms, they transfer nutrients to themselves, contributing to the cycling and recycling of nutrients within the ecosystem. Furthermore, some species of holometabolous insects in their adult stage become food sources for other organisms, such as butterflies and bees.

2 Predatory Behavior of Holometabolous Insects

2.1 Predatory behavior characteristics during the larval stage

The larval stage of holometabolous insects is the most active period in their life cycle and also the most frequent and effective stage of their predatory behavior. Many holometabolous insect larvae are carnivorous, primarily feeding on other insects, carrion, maggots, and other small animals. The larvae typically have strong mandibles in their head region, which they use to crush their prey. Some larvae can even chew on prey larger than themselves.

The larvae of some holometabolous insect secrete a sticky substance to capture prey. This secretion allows them to adhere to their prey, making it difficult for the prey to escape. Many larvae of holometabolous insect can also camouflage themselves by altering their body shape or color to better capture their prey (Stevens and Merilaita, 2009). Some larvae hide within plant flowers or leaves, allowing them to approach their prey more effectively.

In conclusion, the larval stage of holometabolous insects exhibits various predatory behavior characteristics, enabling them to efficiently prey on their targets, ensuring their survival and development.

2.2 Predatory behavior characteristics during the pupal stage

The pupal stage of holometabolous insects is a transitional phase between the larval and adult stages, during which significant morphological and physiological changes occur within their bodies. In comparison to the larval stage, the predatory behavior of holometabolous insects during the pupal stage is more limited and mainly characterized by the following aspects:

During the pupal stage, holometabolous insects are typically in a dormant state. The holometabolous insects in their pupal stage are in a dormant state, lacking the ability for active predation. They solely rely on the stored nutrients within their bodies to support their growth and development. Some holometabolous insects in the pupal stage retain limited predatory capabilities, but their hunting behavior is usually simpler compared to the larval stage. For instance, some insects in the pupal stage use secretions or solid substances from their mouthparts to capture prey. Pupal-stage insects may also become prey for other organisms. Holometabolous insects in the pupal stage are often more vulnerable and can be easily preyed upon by other animals. For example, certain birds may prey on pupal-stage insects such as butterflies and bees.

2.3 Predatory behavior characteristics during the adult stage

The adult stage of holometabolous insects is their final developmental stage, and it is also the stage where their predatory behavior is most diverse and complex. The predatory behavior of holometabolous insects during the adult stage exhibits a wide range of diversity and complexity, including various feeding habits, flying abilities, adaptability of mouthparts, and capturing skills. These characteristics enable holometabolous insects in their adult stage to adapt to different ecological environments and acquire multiple sources of nutrients, ensuring their survival and reproduction.

The adult stage of holometabolous insects exhibits a wide variety of feeding habits, with some being herbivorous, others carnivorous, and still others being omnivorous. Different species of adult insects have varying dietary preferences, and they select different types of food to obtain nutrition (Krenn, 2010).

Holometabolous insects in their adult stage typically possess strong flying abilities, enabling them to fly to different locations in search of food. For instance, insects like butterflies and bees can find nectar and other food sources through flight (Figure 2).

During the adult stage, holometabolous insects typically have mouthparts adapted to different types of food. For instance, some insects have mouthparts suitable for sipping nectar from flowers (Figure 3), while others have mouthparts adapted for biting plants or other insects.

Some holometabolous insects in their adult stage can capture other insects as food. For example, dragonflies typically possess rapid response speed and agile capturing techniques.

3 Predation Strategies of Holometabolous Insects

3.1 Adaptability of predatory behavior

The predatory behavior of holometabolous insects demonstrates strong adaptability, enabling them to survive and reproduce in various ecological environments, food sources, and hunting techniques. This adaptability allows them to thrive in diverse ecological conditions.

The larvae of holometabolous insects can live in water and prey on insects and proteins in aquatic environments, while other insects primarily adapt to terrestrial environments, hunting plants, other insects, and carrion. Unlike most carnivorous insects, holometabolous insects can also feed on nectar and plant juices (Harvey and Gols, 2011). The larvae of holometabolous insects can secrete mucous to capture prey, while other insects rely on their quick chasing abilities or use ambush and sudden attacks to capture their prey.

Furthermore, the predatory behavior of holometabolous insects can adapt throughout different stages of their life cycle. For example, some insects are carnivorous during their larval stage, but become herbivorous during their adult stage, or vice versa, where they are herbivorous during the larval stage but turn carnivorous during their adult stage.

3.2 Modes of attack during predation

The modes of attack during predation by holometabolous insects are diverse and vary depending on the insect species, life stage (larva or adult), feeding habits, and environmental factors. Common attack modes include biting, sipping, capturing, secreting mucous, and ambushing.

Many holometabolous insects use biting as a way to prey on their targets. For example, some beetle larvae will crush the prey's exoskeleton and then consume its internal tissues. The adults of these insects also have strong biting forces that can crush or tear the prey into small pieces (Krenn et al., 2005). Some holometabolous insects in their adult stage use sipping as a means of obtaining food, such as sipping nectar or leaf juices. These insects typically have elongated mouthparts that can penetrate through flower petals or leaves to directly extract the fluids. Certain holometabolous insects, such as butterflies and moths, capture other insects or small animals to obtain food. They employ rapid flight and agile capturing techniques to catch other insects. Some holometabolous insect larvae secrete mucous to capture their prey. For instance, some larvae of Mythimna separata (Walker) produce mucus to trap other insects and small animals. Additionally, some holometabolous insects in their adult stage employ ambush tactics to capture their prey.

In general, different holometabolous insects will adopt various attack modes in different situations, and these attack modes are often related to the insect's ecological environment, feeding habits, and life cycle.

3.3 Localization methods during predation

The localization methods used by holometabolous insects during predation are diverse and depend on factors such as the insect species, life stage (larva or adult), feeding habits, and the environment. These localization methods are often related to the insect's sensory abilities and body structure, as well as the size, speed, and defensive capabilities of the prey. Common localization methods include visual localization, olfactory localization, auditory localization, sensory localization, and tactile localization.

For example, moth larvae can locate food by sensing chemical substances in the air, cicadas and crickets, among other insects, locate their prey by hearing the sounds they produce, and ant larvae can use their sense of touch to perceive their surroundings and the position of their prey.

4 Impact of Predatory Behavior of Holometabolous Insects on Ecological Role

4.1 Pest population control

The predatory behavior of holometabolous insects has a significant impact on controlling pest populations, as they play a crucial role as important natural predators.

Holometabolous insects typically feed on other insects, which allows them to help regulate the number of pests. For example, dragonflies prey on mosquitoes and other small insects (Figure 4), ants prey on aphids and other small insects, and so on. These holometabolous insects maintain their ecological balance by preying on pests, thereby reducing the pest population and safeguarding the health of plants and crops.

In addition, the predatory behavior of holometabolous insects can also reduce the reliance on chemical pesticides. When faced with an excessive pest population, farmers may resort to using chemical pesticides for control. However, these chemical pesticides can pose certain risks to the environment and human health. The predatory behavior of holometabolous insects can help to reduce the reliance on chemical pesticides to some extent, thereby minimizing the hazards to environment and humans.

Therefore, the predatory behavior of holometabolous insects is highly beneficial for conserving the ecological environment and agricultural production. They can aid in controlling pest populations, reducing the need for chemical pesticides, and thus safeguarding ecological balance and human health.

4.2 Impact on pest population structure

The predatory behavior of holometabolous insects has complex effects on the structure of pest populations. They can influence the pest population structure through mechanisms such as controlling pest numbers, influencing pest distribution, and promoting pest diversity.

Holometabolous insects impact the population structure of pests by reducing their numbers through predation. When pest numbers decrease, the competition among pests also diminishes, leading to changes in the pest population structure. For instance, if certain pests are controlled by holometabolous insects, the population of other pests may increase accordingly, resulting in shifts in the pest population structure.

The predatory behavior of holometabolous insects can influence the distribution of pest species. Some holometabolous insects have a wide-ranging diet, allowing them to prey on various types of pests. By controlling multiple pest species, these holometabolous insects impact the distribution of pests. Moreover, their predation behavior can also affect the diversity of pest species. The diversity of pest species depends on the competition and predation relationships among pests. Holometabolous insects reduce pest numbers and competition through predation, thus promoting the diversity of pest species.

4.3 Impact on the balance of ecosystem

The predatory behavior of holometabolous insects has a significant impact on the balance of the ecosystem. They contribute to maintaining the ecosystem balance by controlling pest populations, sustaining the food chain, and influencing ecological diversity.

Holometabolous insects control pest populations through predation, preventing excessive pest reproduction and minimizing damage to plants and crops (Symondson, 2002). This helps maintain the balance of the food chain within the ecosystem and ensures the stability of the entire ecosystem.

The predatory behavior of holometabolous insects can influence the diversity of the ecosystem. They promote ecological diversity by controlling pest populations and influencing the distribution of pests. For instance, when certain pests are controlled by holometabolous insects, other insect species may increase in response, thus enhancing the ecosystem diversity.

The predatory behavior of holometabolous insects can also influence the abundance and distribution of other species within the ecosystem. By affecting the food chain and ecological diversity, they exert an impact on other organisms, helping to maintain the balance of the ecosystem.

In conclusion, the predatory behavior of holometabolous insects has a crucial impact on the balance of the ecosystem. They play a vital role in maintaining ecosystem balance by controlling pest populations, sustaining the food chain, and influencing ecological diversity, thus ensuring the stability of the ecosystem.

5 Conclusion

The predatory behavior of holometabolous insects is the key to their ecological role. These insects are essential predators in natural ecosystems, effectively controlling pest populations through predation and parasitism, thus reducing the hazards of pests and ensuring the health and stability of the ecosystem. Holometabolous insects have a wide range of prey, including various pests, insects, snakes, lizards, etc., which helps maintain the population and proportion of various species in the ecosystem, promoting species diversity and ecological balance. Furthermore, the predatory behavior of holometabolous insects also aids in controlling the spread of infectious diseases, safeguarding the health and safety of humans and animals.

Research on the predatory behavior of holometabolous insects contributes to promoting the sustainable development of agriculture. The extensive use of chemical pesticides can cause pollution and damage to the ecological environment, while the predatory behavior of holometabolous insects can reduce the use of chemical pesticides and mitigate their negative impact on the environment. Studying the predatory behavior of holometabolous insects allows us to understand their effectiveness in controlling various pests, providing farmers with scientific pest control measures to enhance crop yield and quality. Ecological balance helps maintain the stability and health of ecosystems, protecting soil, water resources, and biodiversity, ensuring the guarantee for the sustainable development of agriculture. The predatory behavior of holometabolous insects also reduces agricultural production costs. Farmers no longer need to purchase expensive chemical pesticides in large quantities or invest more manpower and resources in pest control. This, in turn, lowers production costs and enhances the economic benefits of agriculture.

In conclusion, the predatory behavior of holometabolous insects promotes species diversity and ecological balance, safeguarding the health and stability of ecosystems. It plays a crucial role in maintaining the ecological functions and services of ecosystems. Moreover, research on the predatory behavior of holometabolous insects contributes to advancing the sustainable development of agriculture. It can reduce the usage of chemical pesticides, enhance crop yield and quality, promote ecological balance, and lower agricultural production costs. These are all essential goals for sustainable agricultural development.

Authors’ contribution

XMY was responsible for the literature review, organization, and initial drafting of this review. GTX participated in the discussions and paper revisions. XJ was the supervisor of this review, providing guidance in writing and revising the paper. All authors read and approved the final manuscript.

Acknowledgement

This review was supported by the Funding for Cuixi Innovation Research&Development Project of Cuixi Academy of Biotechnolo, Zhuji. We express our gratitude to the experts and scholars cited in the references, as their research findings provided theoretical support for the exploration process.

References

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Some holometabolous insects in their adult stage can capture other insects as food. For example, dragonflies typically possess rapid response speed and agile capturing techniques.