Imagine a world without insects. Often depicted as nuisances in our comfortable lives, the idea of an insect-free world might initially sound great and appealing to someone living in a high-rise building or attempting to clean an overflowing dustbin. But, upon deeper reflection, this notion becomes more complex. In reality, an insect-free world is not just unappealing — it’s a catastrophic idea that would disrupt the food chain and upset the delicate balance of our ecosystem. 

But why discuss this if insects appear to be thriving? We delve into this topic because our world is gradually transforming due to the ongoing effects of climate change, quietly but significantly altering the lives of these creatures. 

Insects — ectotherms reliant on external temperatures — are particularly susceptible to these alterations, where temperature dictates their presence and abundance. 

Heat, dryness, and survival

Ectotherms, owing to their physiological dependence on ambient temperature, face heightened risk due to their small size and high surface area-to-volume ratio. This dynamic often leads to potential dehydration, with insects losing over 80% of their body water through their tough cuticles, which serve as permeable membranes regulating water balance. Such dehydration significantly influences both their survival and reproduction. The fitness of an organism, crucially reliant on its reproductive capacity, relies on suitable temperature and humidity conditions for optimal survival and reproductive success. 

The projected impacts of global warming and desertification paint a concerning picture, creating habitats with limited water availability and reduced humidity, further challenging the survival of these creatures. 

Understanding the impact of drier habitats and reduced humidity on reproductive fitness necessitates studying populations under natural or near-natural conditions. At Ahmedabad University, Subhash Rajpurohit and his research group have undertaken the task of collecting data on humidity and fecundity. This data is sourced from both outdoor mesocosms, mimicking natural environments, and indoor mesocosms, maintaining controlled, constant temperatures. Through the analysis of these datasets, the goal is to uncover the potential influence of relative humidity (RH) on fecundity in fruit flies (Drosophila melanogaster). This research offers invaluable insights into how fluctuating humidity levels might affect insect reproduction in the context of future climates.

What does the data say?

This study takes a closer look into the metabolic adaptations of tropical fruit flies (Drosophila melanogaster) when subjected to the stress of drying out, also known as desiccation, investigating how their metabolic pathways respond to dehydration. It reveals that prolonged dehydration poses challenges in finding a mate for these flies. Female flies experiencing water scarcity exhibit extended courtship behaviors. Also, the duration of dehydration correlated with the time taken for flies to initiate mating and the frequency of failed mating attempts. Interestingly, this dehydration stress doesn’t affect the duration of the actual mating process, mirroring patterns observed in fly populations from cooler regions. 

The research uncovers significant shifts in the utilisation of starch, sucrose, galactose, and amino acids such as phenylalanine, tyrosine, and tryptophan by insects during this stressful period. Notably, it highlights the crucial role of carbohydrates for fruit flies under desiccation, as they strategically prioritise carbohydrate consumption to acquire more water. Carbohydrates yield a substantially higher total amount of water after metabolism compared to lipids, showcasing the flies’ adaptive approach to water acquisition during challenging conditions.

Rajpurohit, who conceived the idea and designed the experiment, remarks, ​“Many insects are key players in ​‘crop-pollinator’ dynamics, confronting challenges posed by droughts and rising temperatures”. He adds,

A systematic and in-depth approach encompassing insect physiology could establish the foundation for understanding the responses of insect species to contemporary climatic trends. Ultimately, this could aid in predicting broader species distribution and population dynamics in the future.

Managing stress with sugar

The study also sheds light on the galactose metabolism pathway, revealing its potential role in the fruit flies’ response to desiccation. This pathway closely links to the synthesis of trehalose, a protective sugar that the flies produce under stressful conditions. The researchers also found intriguing alterations in amino acid pathways, emphasising their vital involvement. These findings are similar to what’s observed in other species, underscoring the universal importance of these pathways in reproductive fitness and health.

In essence, this research delves into how environmental stress, like drying out/​dehydration, affects the functioning of fruit flies’ bodies. By exploring these metabolic intricacies, the study enriches our understanding of how insects, like fruit flies, cope and adapt to different environmental conditions. These findings offer valuable insights into the clever survival and reproductive strategies employed by these tiny creatures when confronted with environmental challenges.

Meet the EEE (Experimental Ecology and Evolution) lab 

The Experimental Ecology and Evolution (EEE) laboratory, led by Subhash Rajpurohit at the Ahmedabad University, studies insect physiology at its core. Presently, the lab is focused on comprehending rapid adaptations through cuticular hydrocarbons (CHCs), an area of research that has been relatively underexplored. Although the laboratory specialises in the study of physiological adaptations, it also places importance on genomic insights. 

While this study predominantly delved into the thermal stress response, the ongoing research in the laboratory extends to investigating other environmental stressors and the physiological responses to diverse selection pressures. The findings from the EEE lab are not limited to laboratory experimentation but are also corroborated by outdoor experiments and, more importantly, from natural populations.

Divita Garg, a doctoral candidate studying trait variation in Drosophila wings, notes, ​“The evolution of wing pigmentation patterns is influenced by a complex interaction of natural and sexual selection. The balance between these forces can vary across species and environments. Continued research and interdisciplinary approaches are essential in unraveling the intriguing aspects of wing trait evolution in evolutionary biology”. In addition to understanding the evolution of specific wing patterns across species, she also explores potential connections between wing behavioral patterns and life-history traits.

Harshad Mayekar, a post-doctoral fellow in the lab, explores how environmental pressures influence adaptability during the pupal stage of insects, focusing on Drosophila species. He highlights the significance of examining how slight environmental changes can selectively impact survival dynamics, especially given the limited mobility of the pupal stage. Mayekar emphasises that juvenile stage responses to environmental selection pressures need further exploration in insects. 

Abhishek Nair, a doctoral candidate in the lab, is dedicated to studying desiccation tolerance in natural populations of Drosophilid. His research focuses on understanding how small ectotherms, like Drosophilids, manage water loss by regulating a surface waxy coating called ​‘cuticular hydrocarbons (CHCs)’ when faced with extreme temperatures. Nair emphasises the critical role of a diverse array of CHCs in facilitating their adaptation to environmental challenges.