Key questions for future research in Physiological Entomology

Abstract

Physiological Entomology—the study of how insects work—can contribute to basic understanding of biology and evolutionary adaptation as well as inform insect conservation and pest management. We are keen to emphasise the breadth of the subject and how it is relevant to wider contemporary scientific developments such as big data and genomics.

In a horizon scanning exercise, editors of Physiological Entomology considered key questions for future research in the subject, and these form the subject of this editorial.

This article was developed in the wider context of raising awareness of Physiological Entomology and highlighting the broad scope and relevance of the journal to help the community frame research questions at the forefront of our discipline (Bruce et al., 2024).

All these themes concern physiological mechanisms by which insects can increase their evolutionary fitness (ability to survive and reproduce) (Orr, 2009). The core themes are shared by all animals and reflect the increasingly integrative nature of insect physiology. For example, senses are required for perception of the environment and other organisms, are modulated by phenotypic plasticity including learning behaviour and play key roles in finding mates and food for reproduction and nutrition.

Environmental adaptation is a major theme in Physiological Entomology. Indeed, if we were to rename the journal, ‘Insect Environmental Adaptations’ could perhaps be a strong contender. Questions raised range from why insects are so successful at adapting to the environment in general, to more focussed aspects such as adaptation to cold stress (Lemay et al., 2024), heat stress (Huang et al., 2024) or starvation (Lenhart et al., 2024). It is remarkable that insects are the most successful animals both in terms of number of species and in terms of biomass. It is estimated that there are 5.5 million species of insect (Stork, 2018) and 1 gigaton of carbon biomass globally (Bar-On et al., 2018). Interest in understanding environmental adaptations in insects arises from several viewpoints. Besides understanding the processes responsible for evolution of the amazing biodiversity of insects, research is conducted to address how they deal with challenges posed by environmental stresses and what factors suppress insect propagation to provide measures for pest control (Piersanti et al., 2023).

Insects have evolved a suite of adaptations to cope with biotic and abiotic stressors. What is the extent of these adaptations, and why do some species have narrow ranges while others have broad distributions? (Bonadies et al., 2024). This question is important and timely because of accelerating climate change and its probable effects on agriculture and food security as well as human and animal disease transmission (Dwyer-Joyce et al., 2025). How are insects adapted to their environment? What constrains their ability to function in specific environments (Figure 1), and how do insects cope with changes in these factors? These key questions are essential to understand establishment and sustainability of insect populations and how communities form and change.

Insects can respond to stressors in several ways. However, the most rapid response is likely a behavioural one. Avoidance, repellence and flight are all responses that can occur very quickly (Humphreys & Ruxton, 2019; Nansen et al., 2016). Other physiological responses, such as the integrated stress response or changes in the developmental programme (Polenogova et al., 2024), take time to occur because they involve processes from gene expression to changes in protein activities, metabolic pathways, cell and organ function and ultimately switching between phenotypes. Thus, addressing the ways in which insects have adapted to environmental stressors requires looking across levels—from molecular processes for coping with stress to organismal behaviours that allow insects to avoid these stressors.

Other organisms can be seen as the ‘biotic environment’ and therefore the question of how insects adapt to their environment must necessarily encompass how insects interact with other organisms. These interactions span a continuum from beneficial mutualistic symbioses to exploitative interactions such as parasitism and predation (Figure 2). However, interactions with other organisms are more complex than interactions with the abiotic environment because the other organisms are also evolving and adapting. As physiological entomologists, we are interested in the mechanisms that allow insects to successfully navigate these interactions. These mechanisms may include physiological adaptations to parasites in insect species of economic relevance, such as the honeybee (de Oliveira et al., 2023) and agricultural pest species (Oyeniyi et al., 2024), or using experimentally tractable model systems like mealworm beetles and fruit flies to dissect defence mechanisms such as immune priming (Subhagan et al., 2025) and disease tolerance (Prakash et al., 2025).

Pathogens and parasites are biotic ‘stressors’, and avoidance of infectious substrates or conspecifics is an insect's first line of defence and a topic of enormous interest within evolutionary ecology (Gibson & Amoroso, 2022). A major frontier in the subject is understanding the neuro-immune physiology that allows insects to detect the olfactory, gustatory and visual cues of infection and how insects use these cues to modify their behaviour, immune physiology and general life-history (Milutinović & Schmitt, 2022). While most of this work has been carried out in a few choice model systems (Masuzzo et al., 2020), there is a void in our knowledge of similar physiological responses in most insect taxa. A related and very exciting topic is that of self-medication in insects in response to environmental toxins (Erler et al., 2024). Key questions remain regarding the prevalence of prophylactic self-medication in animals, and studies in insects are leading the way in addressing these questions, such as the relative costs and benefits of self-medication, as well as the role of medication in immune modulation, and physical or chemical interference with pathogens and beneficial microbes (Erler et al., 2024).

Insects themselves are often parasites that need to adapt to other animals to maximise fitness, hence, further interest lies in the strategies insect parasites use to settle on their hosts (Büscher et al., 2022). A key feature of many insects is their ability to serve as vectors for disease, and we also considered what physiological factors are required, and why some insects are highly efficient disease vectors (Oliveira et al., 2020). The question is timely given the extremely high prevalence of established insect-vectored infections (e.g., malaria, dengue, Zika) but also due to the increased incidence of these infections as a warming climate allows insects to expand their range to new geographical regions (Paz, 2024). Here, the interface between ecology and physiology is highly relevant to both public health and crop protection from vectored plant pathogens (Shrestha et al., 2024) and can inform how insects adapt simultaneously to their rapidly changing abiotic environment while also maintaining the physiology that makes them competent disease vectors.

Another major theme was phenotypic plasticity and development (Whitman & Agrawal, 2009). Insects have remarkable phenotypic plasticity with different morphs and life stages. Insects that undergo metamorphosis have the same genotype but an incredible transition from larval to adult phenotype. Social insects have different castes performing different roles. Insects such as aphids with complex life cycles can have sexual and asexual morphs on winter and summer hosts, as well as winged and wingless forms (Corona et al., 2016).

Interactions of insects change during their development. Tasks differ between insect stages, such as eggs, juveniles and adults (Salerno et al., 2022), especially if the foraging mode changes during development (Figure 3). To understand population dynamics and intraspecific interactions, as well as stage specific interspecific relationships, understanding the life history throughout development is crucial for pest control, conservation and ecological research. These conditions can also be subject to climate change.

The control of time, as represented by lifespan, may be an important research topic in insects. In homeothermic animals such as mammals, the time from development to lifespan is almost fixed. In many insects, however, the developmental rate and lifespan vary greatly depending on photoperiod and temperature. The underlying mechanism has been studied for a long time but still largely remains to be elucidated. This feature could be used to study how biological time is regulated, and the results may promote our understanding of the nature of ageing and lifespan in animals beyond insects.

Many insects have a phenomenal reproductive capacity. This helps to explain why certain species become pests in some environmental contexts. Strategies to maximise reproductive output require various steps in reproductive processes. Increasing egg numbers and mating increases the quantity of potential offspring, while egg placement (Sawadogo et al., 2022) and parental care (Kirschman et al., 2022) increase likelihood of survival of these numbers. Beyond finding answers on how the production of fertilised eggs and their survival is increased, key questions in reproductive physiology include the isolation barriers that contribute to speciation, and responses to external factors that require adjustment to maintain reproduction. Besides mechanical barriers in the morphology and fit of genitals (see Simmons, 2014), recognition of mating partners (Figure 4) is a long-standing question in entomology. These interactions give rise to questions concerning the influence of the individual history of pheromone sensing, which can have an influence on mating behaviour (Gavara et al., 2022), and the drivers of intraspecific reproductive isolation, which can include incompatible microbiota (Macagno & Moczek, 2023).

Beyond the interactions of mating partners and the balancing of offspring number and egg quality (Alqurashi et al., 2023), we recognise an increasing interest in understanding the strategies employed by insects to increase survival of eggs (Büscher et al., 2023; Debruyn et al., 2025; Hilker et al., 2023; Li et al., 2024).

All animals must balance their constantly changing demand for nutrients against their supply in foods, a balance that can be influenced by numerous biotic and abiotic factors. Although enormous advances have been made using synthetic diets in terms of knowing what nutrients are required and in what proportions and what the life history consequences are for many insects, there is still an enormous gap in our understanding of what enters the mouth and what an insect actually absorbs, together with the physiological impacts of nutrient variation at the micronutrient level and how this affects trade-offs to growth, development, reproduction immune function and ageing.

Nutritional physiology has a long tradition in entomology detailing various aspects of food uptake (Figure 5), processing and metabolism in insects (House, 1961). There is a large amount of literature on which nutrients and in what proportions optimise growth, development and reproduction for numerous insect species. Recent studies in Physiological Entomology provide insights into effects on reproductive investment (Phạm et al., 2024) based on nutrient quality, processes during insect starvation (Zhang et al., 2022) and thermal resistance regulation of nutritional development (Phungula et al., 2023). Insects represent a promising food source for humans, hence, investigating growth optimisation is a persistent question. However, gaps exist regarding the optimisation of artificial diets. These artificial diets can be powerful in optimising productivity of cultured insects, but the balance between uptake and absorption is not fully understood. The translation of insights on artificial diets into natural food is furthermore useful for conducting experimental studies. We recognised key open questions in understanding what happens between ingestion and life history outcome. Most research has concentrated on understanding the consequences of feeding, but ingestion does not necessarily equal digestion (Holdbrook et al., 2024). Insects possess both morphological and physiological tools to obtain nutrients, but neither their evolution nor how plastic these traits are is well understood. Particularly, addressing the translation from what is known from the use of synthetic diets to ‘real’ food needs to go beyond grinding up plant tissues and measuring their chemical composition to inform about the ecological situations. For example, mouthparts of herbivorous insects feeding on the leaves of flowering plants correspond to the anatomy of the plant diet and differ between the food preferences (Krenn, 2019). While some insects are specialists, others are generalists, raising questions on the implications of the effect of climate change on plant leaves and their consumption. Within the same framework it is interesting to see how much plasticity insects have to redress nutrient imbalances when ingesting suboptimal diets. Locusts, for example, can change the ratio of protein to carbohydrate absorbed through differentially releasing proteases and carbohydrases (Clissold et al., 2010) and by using thermoregulatory behaviour (Clissold et al., 2013; Coggan et al., 2011).

Further impact of insects to human nutrition arises from the role of insects as crop pests and pollinators. Here, protection of crops requires insights from nutritional biology as well. Understanding effects of secondary plant metabolites (Michereff et al., 2022) and insecticides (Esmaeily et al., 2022) taken up by pests aids in increasing protection of crops and reducing secondary losses of biodiversity.

Another question identified is the role of physiological sensing of nutrients by means of food processing. Compounds of ingesta are not equally registered during disassembly and might have different behavioural response depending on the presence of key compounds. This raises open question on understanding nutrient sensing and how this affects processes such as intake, gut emptying rate and allocation once absorbed (Holdbrook et al., 2024). Nutrient concentration in the haemolymph influences food choice, intake rate and allocation, but this connection is poorly understood (Simpson & Raubenheimer, 1993; Tetlak et al., 2015). For example, when ingesting leaves gut emptying rate appears to be a key determinant influencing not only the rate of total nutrient gain, but also the ratio of proteins to carbohydrates being absorbed.

The questions outlined above are not mutually exclusive and overlap in many cases. They provide an indication of what we would like to learn about insect physiology. All the questions address various aspects of insect evolutionary fitness (Orr, 2009). How insects adapt to the environment, interact with other organisms, adjust their phenotype, reproduce and obtain nutrition are all related to survival and reproduction and therefore fitness. However, Physiological Entomology views insect fitness through a mechanistic lens and asks specific questions—What are the exact mechanisms that allow insects to survive and reproduce? Why is one phenotype more adaptive than another? And most fundamentally, how do insects work?

Insects are tractable model systems for addressing key questions in biology and, in the post-genomics era, ‘how insects work’ is particularly relevant for functionally characterising what genes do. The enormous adaptive capacity of insects and their tremendous biodiversity make them ideal organisms for understanding how evolution works at different levels and renders them a suitable general model for studying evolutionary processes. The amount of information at the genetic and genomic levels, along with sophisticated experimental techniques, can help to address different evolutionary problems and issues of selection and adaptation at different levels.

Beyond the identification of key questions, Physiological Entomology faces the challenge of transformative processes of the field in general. Physiology itself transformed over the years from an originally central academic field to an increasingly interdisciplinary one. Now that it has become related to a wide range of fields from the gene level to conservation, the scope of the journal grows more into interdisciplinary fields related to physiology. Physiological Entomology embraces contributions with a wide range of interdisciplinary perspectives.

Insect physiological studies are helpful in addressing challenges for applied research such as biodiversity conservation and pest management. The grand challenges in entomology were recently framed by the Royal Entomological Society (Luke et al., 2023) and provide wider context.

We welcome review articles as well as original experimental studies addressing any of the questions outlined in this editorial and indeed any further topics that we may have missed that could advance understanding of Physiological Entomology.

Thies H. Büscher: Conceptualization; writing – original draft. Arthur G. Appel: Conceptualization; writing – review and editing. Tim Lüddecke: Conceptualization; writing – review and editing. Vladimir Kostal: Conceptualization; writing – review and editing. Pedro F. Vale: Conceptualization; writing – review and editing. Fiona Clissold: Conceptualization; writing – review and editing. José L. Maestro: Conceptualization; writing – review and editing. Hideharu Numata: Conceptualization; writing – review and editing. Kenji Tomioka: Conceptualization; writing – review and editing. Nicky Wybouw: Conceptualization; writing – review and editing. Nicholas Teets: Conceptualization; writing – review and editing. Toby J. A. Bruce: Conceptualization; writing – original draft.

The authors declare no conflicts of interest.