Why has the use of insects as biological models in behavioural ecology been so successful? The first reason is, without question, their diversity. Class Insecta contains the largest number of species in Animalia [1]. They have colonized all terrestrial ecosystems and present a huge diversity of life history traits and behaviours that makes them fascinating organisms to answer the key historical question in behavioural ecology, that is, what is the adaptive value of observed behaviours in different environments? The second reason is their size. Thanks to their small size, and thus to our ability to rear them easily in many cases, insects always were — and still are — wonderful biological models for running laboratory experiments. Over the years, this has enabled us to address important questions related to animal behavioural ecology, leading us both to verify experimentally existing model predictions and to foster further theoretical developments. Such a strong dialogue between theoretical and experimental work on insects has greatly contributed to the development of our current knowledge of behavioural ecology in general. Since the 70s, studies on the behavioural ecology of insects have tried to understand the adaptive value of decision-making processes adopted by individuals in different environmental contexts. One striking example concerns the optimal decisions adopted by reproductive animals. This is the case, for example, for the optimal clutch size and the optimal sex ratio females should lay, or the optimal time foraging animals should remain on patches of resources. In this respect, insect parasitoids are one the most studied guilds of insects, leading to a large number of important findings (see e.g. [2–4]). This classical approach is always fruitful, and determining the adaptive value of behaviour is always at the core of this scientific field [5]. In the Special Issue, three papers illustrate such a classical approach, and develop new ideas and concepts on nutritional ecology, mate choice and polyem-bryony. Raubenheimer and Simpson present an integrative approach — nutritional geometry — that brings together two historical disciplines: foraging and feeding. Nutritional geometry allows us to model graphically and elegantly the interactions between different diet components and their effects across several levels, including physiology and ecology, on individual behaviour and reproductive success. Such a promising approach, which has yet to be used in the field in insects, should allow us to integrate all facets of nutritional activity in animals. Another classical question in behavioural ecology is sexual selection and particularly mate choice. Kelly presents recent research on the identification of factors — both intrinsic and extrinsic — of the females explaining variation in their mate preference for sexually selected traits in males. Eric Wajnberg is a population biologist, specialized in population genetics, behavioural ecology, statistical modelling and biological control. For over thirty years, he developed several scientific programmes leading to better understand what are the most important behavioural traits involved in the efficacy of insect parasitoids to control crop pests in biological control programmes. Theoretical approaches are developed — mainly using Monte Carlo simulations and Genetic Algorithms — and experiments are conducted in order to verify the predictions obtained. The main traits studied are (1) those involved in progeny and sex allocation (sex ratio), (2) locomotory mechanisms involved in discovering hosts (video tracking), (3) patch exploitation strategies, etc. He is the editor-in-chief of the international journal BioControl and has published more than 10 books on insect ecology and biological control.