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Adaptation of life-history traits is an important factor for the success of insects. Voltinism is a feature that descends from several life-history traits and, given that the latter depend on the s...

Harmonic entomological radars have been used in the last decades to track small and lightweight passive tags carried by various insects, usually flying at low altitude and over flat terrain. Despite being exploited in many applications, not a lot of progress was achieved in terms of performances over the years. This paper reviews the research work done in this topic throughout the European LIFE project STOPVESPA, from 2015 to 2019. The main objective of LIFE STOPVESPA was to contain the invasive Asian hornet (Vespa velutina) and prevent it from further invading Italy. Among the foreseen activities, a new harmonic radar has been developed as an effective tool to locate the hornets nests to be destroyed. A preliminary prototype, based on a magnetron generator, was tested in 2015, showing a detection range of about 125 m. A first upgrade of this prototype was released in 2016, allowing to increase the detection range up to 150 m. A new approach, based on a solid state power amplifier and a digitally modulated signal, was then adopted for the second prototype developed in 2017 and extensively run in 2018; the detection range raised to 500 m. A last engineered prototype was eventually built for the 2019 summer campaign with additional improvements. This tool has been extensively validated over the last years with the Asian hornet but it has potential for tracking and monitoring many other flying insects.

Harmonic radars can be generally used to track very small (1.5 cm) and lightweight (15 mg) passive tags; as an example, they have been adopted to track various insects for almost 30 years now. In most of the cases, their usage was motivated by the entomological interest in better knowing the habits of the observed insect; in fewer applications, like ours, prevailed the need of protecting the environment from invasive species. However, despite the purpose of the research involving entomological radars, not a lot of engineering resources have been invested during the last decades with the aim of improving what was basically considered a mere tool in the hands of entomologists. The goal of this paper is to show how modern radar techniques, the progresses in the available hardware and a three years long design effort helped us to build and test an harmonic radar system with considerably improved performances. The prototype herein described is able to detect the flight of tagged insects in real time, up to 500 meters with a quite large field of view in elevation, and can be therefore adopted also in harsh environments.

Insects adapt commonly to seasonally changing habitats and reproductive contexts. Individuals that mature at different times during the year can show patterns of life cycle or morphological variation, possibly associated with changes in reproductive behaviour. Concerning mating strategies of flying insects, wing morphology may be related both to the outcome of male–male contests and to the ability in acquiring females. Therefore, different mating strategies (territorial vs. non-territorial) may have different flight morphology optima that increase fitness in their context. Males of Calopteryx splendens are mainly territorial early in the season, but with the advancing season and with increasing competition, more and more males adopt a non-territorial pursuing strategy. Given that different mating tactics have different wing morphologies, here we test whether the wing shape of males shifts from a “territorial” to a “non-territorial morphology” during the season. So, early in the season males show highly sexually dimorphic wings, which allow for high manoeuvrability and larger spots, while late in the season wing shapes of males become less sexually dimorphic and more suitable when pursuing females. Additionally, we studied the seasonal variation of other flight related traits, specifically wing lengths, abdomen length and weight. We found that these latter traits decreased along the season in both sexes without altering sexual dimorphism. However, wing shape, which resulted sexually dimorphic, showed a seasonal variation, decreasing the level of sexual dimorphism. The most probable determinant of this change is phenotypic plasticity triggered by environmental cues, but other explications of the observed pattern are discussed.

Female limited polymorphism consists in the coexistence of two or more female morphs in the same population and is widespread among odonates. Generally, one female morph, the andromorph, resembles males in colour or, sometimes, also in morphology and behaviour, while one or more other morphs, gynomorphs, differ from males. This phenomenon is probably promoted by advantages to females which arise from reduced sexual harassment. Andromorph females of Calopteryx splendens keep wing spots, like males (although these ornaments do not match exactly male wing spot colour), while gynomorphs have hyaline wings. Males and gynomorphs show a marked sexual dimorphism in wing shape, and this determines flight patterns which differ between sexes. If andromorphs mimic male wing spots to avoid harassment, they may also benefit from mimicking the male flight morphology, and consequently the male flight pattern. In this case wing shape of andromorph and gynomorph females would differ, as the wing shape of andromorphs resemb...

Sexual dimorphism is common in animals and derives from two mechanisms: sexual selection and sexual niche divergence. These mechanisms may work together as determinants of wing shape in pigmented wings of Odonata. On the one hand, sexual selection by females tends to enlarge the wing areas of males that host pigments; on the other hand, sex-specific flight behaviours, due to differential niche selection, may promote sexual dimorphism. Both sexes of Sympetrum pedemontanum have ornamented wings with bands, but their function is poorly understood. Therefore, we studied shape and size of wings and wing bands of S. pedemontanum using geometric morphometrics to quantify the extent of sexual dimorphism. We also investigated whether sexual dimorphism in wing shape derives from the effect of sexual selection on wing ornamentation or from sexual niche separation. We found sexual dimorphism in wing shape and in the shapes of the bands, but the absence and misdirection of sexual size dimorphism and wing shape dimorphism of bands do not support the hypothesis that wings and wing bands in S. pedemontanum are subjected to sexual selection. Instead, the pattern of sexual dimorphism in wing shape seems more likely to be caused by sex-specific flight requirements.

Character displacement (CD) is the evolutionary process which leads to the divergence in trait expression of closely related species in regions where species co-occur, compared to allopatric populations. In Europe CD has been investigated in males of Calopteryx splendens and C. virgo and has been related to species recognition. If species recognition is relevant for males, also females should benefit from CD. The most obvious differences between females of these two species are wing profile and colour. We sampled females from allopatric and from sympatric populations with different relative abundances of these species. Wing shape and pigmentation were evaluated for each damselfly. CD was found in wing profile but not in wing transparency. The relative abundance of species significantly affected CD, but with a different pattern in each species. The prediction that wing shape become more different from the allopatric state when the species was relatively rare, but more similar to the allopatric state when the species was common was evident only for C. splendens. Wing shape changes might increase differences in flying patterns making males more effective to discriminate between heterospecific females. So, CD we observed may be the result of a selection directed to reduce interspecific reproductive interference.