The head morphology of Pyrrhosoma nymphula larvae (Odonata: Zygoptera) focusing on functional aspects of the mouthparts

Behavioral Diversity Among Odonata Larvae Increases in Water with Greater Turbidity Under Captivity Conditions

Various factors, including environmental variables, influence the behavior of aquatic insects. However, our understanding of insect behavior and their relationships with these variables remains limited. One important variable is water turbidity, which may be exacerbated by soil erosion, directly impacting visibility in the water and potentially affecting the organism's behaviors. In this study, we investigated larval behavior across seven Odonata species under controlled conditions, examining variations in behavioral diversity (frequency and type) associated with sex and three levels of water turbidity. Our findings revealed that heightened water turbidity correlated with increased behavior frequency, possibly attributable to predator avoidance in darker, seemingly safer habitats. Furthermore, behavior diversity differed between sexes, being higher for males in certain categories and for females in others. Anisoptera species predominantly displayed behaviors like resting, eating, and prey capture, whereas Zygoptera larvae were often observed perching and walking, possibly indicative of distinct predator response strategies. Behaviors shared by Anisoptera larvae could be associated with similar responses to predators and capture of prey. Our study found an increased frequency of behaviors when the larvae are in water with higher turbidity. Behavior frequency disparities between the sexes were observed across various behaviors, likely influenced by species-specific activity levels and individual behavioral plasticity in response to environmental cues. Overall, individuals exhibited heightened behavioral activity in environments with elevated turbidity, potentially reflecting a perceived lower risk environment.

A switchable joint in the head of dragonfly larvae (Insecta: Odonata) as key to the multifunctionality of the prehensile labial mask

Dragonfly and damselfly larvae (Insecta: Odonata) capture prey by rapid protraction of a raptorial mouthpart, based on a modified labium. Yet, in insects with biting-chewing mouthparts, the labium has an essential role in food handling. These two distinct functions -prey capturing and handling-lead to a mechanical problem in Odonata larvae: while the labium is always protracted in a straight line during prey capture, food handling requires more dexterity. In this study, we investigate the role of the labium in the feeding process and analyse the mechanics of the labial joints in the dragonfly larva Anax imperator. Our results show that the labium features a multiaxial joint connecting the basal segment (postmentum) and the head. During feeding, a combination of rotations around different axes is used to handle and orient prey, which is unique among biting-chewing mouthparts. Furthermore, we identified structures at the joint which likely restrict lateral motion during the predatory strike. Our results provide a further understanding of the unique prey-capturing apparatus of odonate larvae capable of controlling a 'switchable' multiaxial to a restricted monoaxial joint. This concept highlights the evolution of a highly modified raptorial mouthpart appendage where the degrees of freedom can be actively restricted to allow for the respectively needed functionality.

The mouthparts of the adult dragonfly Anax imperator (Insecta: Odonata), functional morphology and feeding kinematics

Insects evolved differently specialized mouthparts. We study the mouthparts of adult Anax imperator, one of the largest odonates found in Central Europe. Like all adult dragonflies, A. imperator possesses carnivorous-type of biting-chewing mouthparts. To gain insights into the feeding process, behavior and kinematics, living specimens were filmed during feeding using synchronized high-speed videography. Additionally, the maximum angles of movement were measured using a measuring microscope and combined with data from micro-computed tomography (µCT). The resulting visualizations of the 3D-geometry of each mouthpart were used to study their anatomy and complement the existing descriptive knowledge of muscles in A. imperator to date. Furthermore, CLSM-projections allow for estimation of differences in the material composition of the mouthparts' cuticle. By combining all methods, we analyze possible functions and underlying biomechanics of each mouthpart. We also analyzed the concerted movements of the mouthparts; unique behavior of the mouthparts during feeding is active participation by the labrum and distinct movement by the maxillary laciniae. We aim to elucidate the complex movements of the mouthparts and their functioning by combining detailed information on (1) in vivo movement behavior (supplemented with physiological angle approximations), (2) movement ability provided by morphology (morphological movement angles), (3) 3D-anatomy, and (4) cuticle composition estimates. This article is protected by copyright. All rights reserved.

Prey Capturing Dynamics and Nanomechanically Graded Cutting Apparatus of Dragonfly Nymph

Aquatic predatory insects, like the nymphs of a dragonfly, use rapid movements to catch their prey and it presents challenges in terms of movements due to drag forces. Dragonfly nymphs are known to be voracious predators with structures and movements that are yet to be fully understood. Thus, we examine two main mouthparts of the dragonfly nymph (Libellulidae: Insecta: Odonata) that are used in prey capturing and cutting the prey. To observe and analyze the preying mechanism under water, we used high-speed photography and, electron microscopy. The morphological details suggest that the prey-capturing labium is a complex grasping mechanism with additional sensory organs that serve some functionality. The time taken for the protraction and retraction of labium during prey capture was estimated to be 187 ± 54 ms, suggesting that these nymphs have a rapid prey mechanism. The Young’s modulus and hardness of the mandibles were estimated to be 9.1 ± 1.9 GPa and 0.85 ± 0.13 GPa, respectively. Such mechanical properties of the mandibles make them hard tools that can cut into the exoskeleton of the prey and also resistant to wear. Thus, studying such mechanisms with their sensory capabilities provides a unique opportunity to design and develop bioinspired underwater deployable mechanisms.

Odonata

Jessica Ware introduces the insect order odonatan, the damselflies and dragon flies.

A controllable dual-catapult system inspired by the biomechanics of the dragonfly larvae's predatory strike

The biomechanics underlying the predatory strike of dragonfly larvae is not yet understood. Dragonfly larvae are aquatic ambush predators, capturing their prey with a strongly modified extensible mouthpart. The current theory of hydraulic pressure being the driving force of the predatory strike can be refuted by our manipulation experiments and reinterpretation of former studies. Here, we report evidence for an independently loaded synchronized dual-catapult system. To power the ballistic movement of a single specialized mouthpart, two independently loaded springs simultaneously release and actuate two separate joints in a kinematic chain. Energy for the movement is stored by straining an elastic structure at each joint and, possibly, the surrounding cuticle, which is preloaded by muscle contraction. As a proof of concept, we developed a bioinspired robotic model resembling the morphology and functional principle of the extensible mouthpart. Understanding the biomechanics of the independently loaded synchronized dual-catapult system found in dragonfly larvae can be used to control the extension direction and, thereby, thrust vector of a power-modulated robotic system.

Illuminating nature's beauty: modular, scalable and low-cost LED dome illumination system using 3D-printing technology

Presenting your research in the proper light can be exceptionally challenging. Meanwhile, dome illumination systems became a standard for micro- and macrophotography in taxonomy, morphology, systematics and especially important in natural history collections. However, proper illumination systems are either expensive and/or laborious to use. Nowadays, 3D-printing technology revolutionizes lab-life and will soon find its way into most people's everyday life. Consequently, fused deposition modelling printers become more and more available, with online services offering personalized printing options. Here, we present a 3D-printed, scalable, low-cost and modular LED illumination dome system for scientific micro- and macrophotography. We provide stereolithography ('.stl') files and print settings, as well as a complete list of necessary components required for the construction of three differently sized domes. Additionally, we included an optional iris diaphragm and a sliding table, to arrange the object of desire inside the dome. The dome can be easily scaled and modified by adding customized parts, allowing you to always present your research object in the best light.

Material composition of the mouthpart cuticle in a damselfly larva (Insecta: Odonata) and its biomechanical significance

Odonata larvae are key predators in their habitats. They catch prey with a unique and highly efficient apparatus, the prehensile mask. The mandibles and maxillae, however, play the lead in handling and crushing the food. The material composition of the cuticle in the biomechanical system of the larval mouthparts has not been studied so far. We used confocal laser scanning microscopy (CLSM) to detect material gradients in the cuticle by differences in autofluorescence. Our results show variations of materials in different areas of the mouthparts: (i) resilin-dominated pads within the membranous transition between the labrum and the anteclypeus, which support mobility and might provide shock absorption, an adaptation against mechanical damage; (ii) high degrees of sclerotization in the incisivi of the mandibles, where high forces occur when crushing the prey's body wall. The interaction of the cuticle geometry, the material composition and the related musculature determine the complex concerted movements of the mouthparts. The material composition influences the strength, mobility and durability of the cuticular components of the mouthparts. Applying CLSM for extracting information about material composition and material properties of arthropod cuticles will considerably help improve finite-element modelling studies.

Temperature effects on ballistic prey capture by a dragonfly larva

Understanding the effects of temperature on prey–predator interactions is a key issue to predict the response of natural communities to climate change. Higher temperatures are expected to induce an increase in predation rates. However, little is known on how temperature influences close‐range encounter of prey–predator interactions, such as predator's attack velocities. Based on the speed–accuracy trade‐off concept, we hypothesized that the increase in predator attack velocity by increasing temperature reduces the accuracy of the attack, leading to a lower probability of capture. We tested this hypothesis on the dragonfly larvae Anax imperator and the zooplankton prey Daphnia magna. The prey–predator encounters were video‐recorded at high speed, and at three different temperatures. Overall, we found that (1) temperature had a strong effect on predator's attack velocities, (2) prey did not have the opportunity to move and/or escape due to the high velocity of the predator during the attack, and (3) neither velocity nor temperature had significant effects on the capture success. By contrast, the capture success mainly depended on the accuracy of the predator in capturing the prey. We found that (4) some 40% of mistakes were undershooting and some 60% aimed below or above the target. No lateral mistake was observed. These results did not support the speed–accuracy trade‐off hypothesis. Further studies on dragonfly larvae with different morphological labial masks and speeds of attacks, as well as on prey with different escape strategies, would provide new insights into the response to environmental changes in prey–predator interactions.