Euroleon Nostras Research Articles

Divergent venom effectors correlate with ecological niche in neuropteran predators

Neuropteran larvae are fierce predators that use venom to attack and feed on arthropod prey. Neuropterans have adapted to diverse and sometimes extreme habitats, suggesting their venom may have evolved accordingly, but the ecology and evolution of venom deployment in different families is poorly understood. We applied spatial transcriptomics, proteomics, morphological analysis, and bioassays to investigate the venom systems in the antlion Euroleon nostras and the lacewing Chrysoperla carnea, which occupy distinct niches. Although the venom system morphology was similar in both species, we observed remarkable differences at the molecular level. E. nostras produces particularly complex venom secreted from three different glands, indicating functional compartmentalization. Furthermore, E. nostras venom and digestive tissues were devoid of bacteria, strongly suggesting that all venom proteins are of insect origin rather than the products of bacterial symbionts. We identified several toxins exclusive to E. nostras venom, including phospholipase A2 and several undescribed proteins with no homologs in the C. carnea genome. The compositional differences have significant ecological implications because only antlion venom conferred insecticidal activity, indicating its use for the immobilization of large prey. Our results indicate that molecular venom evolution plays a role in the adaptation of antlions to their unique ecological niche.

From individuals to populations: How homo‐ and heterospecific interactions influence habitat selection in a sit‐and‐wait predator

AbstractSpecies have different requirements for the habitat in which they live, depending on various biotic and abiotic factors. For sedentary predators such as antlion larvae, both factors are essential. In this study, we examined the preferred habitat choice concerning two abiotic factors, i.e., substrate and illumination, in two pit‐building antlions, Euroleon nostras and Myrmeleon formicarius, to determine whether choice changes during con‐ or heterospecific interactions. Both species preferred medium sand grains, i.e., 230–540 μm but differed in their choice of illumination. E. nostras preferred shade, while M. formicarius chose the illuminated part of the container. However, the choice changed, especially for M. formicarius during interactions with another individual. Abiotic factors took precedence over biotic factors in the choice of E. nostras when interactions were involved. M. formicarius avoided interactions and built pits in less suitable conditions when suitable locations were already occupied. The results can be applied to the species' natural habitat and life traits. We can confirm that E. nostras is a more competitive species when it comes to providing the most suitable abiotic conditions in the habitat for pit construction.

Antlion larvae localize long distant preys by a mechanism based on time difference.

Pit building antlions Euroleon nostras have been submitted to artificial cues in order to delineate their faculty to localize a prey. Series of propagating pulses in sand have been created from an extended source made of 10 piezoelectric transducers equally spaced on a line and located at a large distance from the pit. The envelope of each pulse encompasses six oscillations at a carrier frequency of 1250 Hz and up to eight oscillations at 1666 Hz. In one set of experiments, the first wave front is followed by similar wave fronts and the antlions respond to the cue by throwing sand in the opposite direction of the wave front propagation direction. In another set of experiments, the first wave front is randomly spatially structured while the propagation of the wave fronts inside the envelope of the pulse are not. In that case, the antlions respond less to the cue by throwing sand, and when they do, their sand throwing is more randomly distributed in direction. The finding shows that the localization of vibration signal by antlions are based on the equivalent for hearing animals of interaural time difference in which the onset has more significance than the interaural phase difference.

Mechanical properties of larval mouthparts of the antlion Euroleon nostras (Neuroptera: Myrmeleontidae) and their correlation with cuticular material composition

The diversity of insects can be explained by their ability to fill various ecological niches, which includes the foraging from diverse sources. The cuticle-based feeding structures interact with the food and show adaptations in shape, material composition and mechanical properties to it. In this study, we focus on the mouthparts of a very prominent ambush predator, the antlion larvae of Euroleon nostras. By nanoindentation, we tested the hardness and the Young’s modulus of the mouthparts, which are significantly harder and stiffer than other insect cuticle structures. To gain insight into the origins of the high values, we studied the degree of tanning using confocal laser scanning microscopy. Additionally, we determined the content of transition and alkaline earth metals by energy dispersive X-ray spectroscopy. We found that the proportions of Zn, Mn, Fe, Cu, Ca, Mg, and Si correlate with the mechanical property values. We also conducted experiments on the breaking stress, the puncturing and biomechanical behaviour of the jaws, which highlighted their extraordinary strength. These findings are not only valuable for biologists, but also for material scientists, as they contribute to our understanding of the origins of mechanical property heterogeneities in insect cuticle.

Morphology and Biology of Third Instar Larvae of the Antlion Euroleon nostras (Geoffroy In Fourcroy, 1785) (Neuroptera, Myrmeleontidae) from Turkey

The morphology of third instar antlion larvae of Euroleon nostras (Geoffroy in Fourcroy, 1785) is described and figured using light and scanning electron microscopy. The specimens were collected in Adıyaman Province, Turkey.

Presence of populations of antlions (Neuroptera: Myrmeleontidae) in Denmark correlates with presence of aeolian sand

ABSTRACT Three species of Myrmeleontidae are currently known from Denmark: Myrmeleon bore, Myrmeleon formicarius and Euroleon nostras. Despite their unique and interesting life history, the faunistics of antlions in Denmark are in need of an update. Here, we primarily use the collections from the Natural Museum of Denmark and the Natural History Museum Aarhus to document the species distribution and richness. The antlion specimens were databased according to the distribution data, and distribution maps were created for each species. The maps are compared to previous analyses of Danish antlion faunistics as well as available online sources. The occurrence of the species in neighbouring countries is also considered. Identification keys to both larvae and adults of the Danish species are provided. Interspecific competition could explain why some locations only contain one species. In Denmark, there seems to be a marked correlation between the occurrence of antlions and the presence of aeolian sand. Aeolian sand is an excellent substrate for the larval funnels and is probably the core habitat of the antlion species occurring in Denmark.

The first records of Chrysopa walkeri (McLachlan, 1893) and Euroleon nostras (Geoffroy in Fourcroy, 1785) (Insecta: Neuroptera) from Belarus

The first records of Chrysopa walkeri (McLachlan, 1893) and Euroleon nostras (Geoffroy in Fourcroy, 1785) from the fauna of Belarus are provided. Brief information on distribution and ecology of these species is given.

Heat wave effects on the behavior and life-history traits of sedentary antlions.

Research on the behavioral responses of animals to extreme weather events, such as heat wave, is lacking even though their frequency and intensity in nature are increasing. Here, we investigated the behavioral response to a simulated heat wave in two species of antlions (Neuroptera: Myrmeleontidae). These insects spend the majority of their lives as larvae and live in sandy areas suitable for a trap-building hunting strategy. We used larvae of Myrmeleon bore and Euroleon nostras, which are characterized by different microhabitat preferences—sunlit in the case of M. bore and shaded in the case of E. nostras. Larvae were exposed to fluctuating temperatures (40 °C for 10 h daily and 25 °C for the remaining time) or a constant temperature (25 °C) for an entire week. We found increased mortality of larvae under heat. We detected a reduction in the hunting activity of larvae under heat, which corresponded to changes in the body mass of individuals. Furthermore, we found long-term consequences of the simulated heat wave, as it prolonged the time larvae needed to molt. These effects were pronounced in the case of E. nostras but did not occur or were less pronounced in the case of M. bore, suggesting that microhabitat-specific selective pressures dictate how well antlions handle heat waves. We, thus, present results demonstrating the connection between behavior and the subsequent changes to fitness-relevant traits in the context of a simulated heat wave. These results illustrate how even closely related species may react differently to the same event.

Tribe Myrmeleontini (Neuroptera: Planipennia: Myrmeleontidae) in Iran.

During a study of the family Myrmeleontidae of Iran, specimens of the tribe Myrmeleontini, housed in Hayk Mirzayans Insect Museum were examined. Specimens of Euroleon nostras and Myrmeleon noacki were identified for the first time from Iran. An identification key, illustrations and distributional maps are presented for the Iranian species of Myrmeleontini.

Antlions (Neuroptera, Myrmeleontidae) from ornithological traps on the Curonian Spit: A three-species community containing a new species

A mixed antlion community is recorded at the “Fringilla” Research Station, “Rybachii” Biological Station, Curonian Spit, Baltic Sea, Kaliningrad Province, Russia; the adults were captured using ornithological traps and the larvae were found on sand dunes around. The ratio of the larval numbers in the mixed colonies of Myrmeleon tschernovi sp. n., Myrmeleon formicarius L., and Euroleon nostras (Geoffr.) is 100: 3: 2. The new species is described, the other two are recorded in Kaliningrad Province for the first time. Morphologically, Myrmeleon tschernovi sp. n. is similar to Myrmeleon bore (Tjed.), being its neighbor in the Baltic Region and occupying its econiche. The most characteristic distinctions between these species are found in the male genitalia and in the larval head chaetotaxy and color pattern.

Pit-builder vs non-pit-builder: advantage of trap building strategy in antlion larvae does not mean greater behaviour diversity

Predators use different foraging modes, ranging from active to ambush predation. We investigated the predatory behaviour of two antlion species, the pit-builder Euroleon nostras and the non-pit-builder Neuroleon microstenus, both considered as ambush predators but with different predatory strategies. Since the pit-builders evolved from non-pit-builders, we focused on the similarities and differences in behavioural patterns and capture success. We found that most behavioural patterns occur in both species, although the non-pit-builder’s behaviour is less stereotypic and exhibits more behavioural patterns than in the pit-builder when comparing behaviour from prey introduction to jaw set without pit-construction. In N. microstenus, two distinct behavioural sequences were noted, which depend on the method of prey carcass clearing. This is the first report describing two methods of prey-carcass clearing in a non-pit-builder: tossing or dropping the prey. We also noted the presence of camouflage in the non-pit-builder, considered as an important mechanism in anti-predator tactics.

Antlions (Insecta: Neuroptera: Myrmeleontidae) of Albania

The Myrmeleontidae fauna of Albania was studied in July of 2012. The study revealed 14 antlion species, which included new records for the country. Among collected species, Myrmeleon hyalinus Olivier, 1811, Euroleon nostras (Geoffroy in Fourcroy, 1785), Macronemurus appendiculatus (Latreille, 1807), Macronemurus bilineatus Brauer, 1868, and Neuroleon arenarius (Navás, 1904) are new records for the Albanian fauna. Sand dune habitat in the national park Divjakë Karavasta represents the northernmost known locality of Myrmeleon hyalinus in the Balkan Peninsula.

Behavioral Plasticity and Variation in Pit Construction of Antlion Larvae in Substrates with Different Particle Sizes

AbstractBehavioral plasticity allows animals to maximize their fitness in a variety of environmental conditions. Trap‐building predators represent case studies in such plasticity as the characteristics of their traps are dependent upon the substrate available. We investigated the effect of sand particle size on pit construction in antlions (Euroleon nostras), sand‐dwelling insect larvae that build pitfall traps to capture prey. The pit construction behavior of the species comprises six stages. When antlions were exposed to different sand particle sizes, their behavior differed in terms of the occurrence and duration of particular stages and in the frequency of jerks produced during sand tossing. Jerk frequency was negatively correlated with sand particle size and also changed during pit construction. Furthermore, at larger particle sizes, individuals occasionally constructed irregular traps with a figure of eight shape, and they crossed the center of the truncated cone during deepening. In the largest substrate, particle size of antlions did not construct pits. Our results demonstrate that variation in traps under differing environmental conditions stems directly from behavioral plasticity in this species.

Effect of substrate density on behaviour of antlion larvae (Neuroptera: Myrmeleontidae)

Sand-dwelling antlion larvae are well known predators with a highly specialized prey-catching strategy, which either construct efficient pitfall traps or bury themselves in the sand ambushing prey on the surface. Although habitat selection in antlions has been extensively studied, little is known about the role substrate density plays in such behavioural decisions. We thus first quantified the natural substrate densities of 13 antlion species by collecting soil samples from 18 different field sites. We found that natural substrate densities varied from 121 g/l to 1562 g/l. The substrate densities of three non-pit-building species (Neuroleon microstenus, Distoleon tetragrammicus, Nophis teillardi) ranged from medium to high, while those of obligatory pit-builders (Euroleon nostras and eight Myrmeleon species) were more variable. The substrate density of the facultative pit-builder Cueta sp. was high. Next, we explored the responses of the pit-building antlion E. nostras to different substrate densities using both a habitat choice and a complementary no-choice experiment. We hypothesized that antlions should be capable of distinguishing between substrate types and that pit size should decrease with increased substrate density. When allowed to choose among eight substrate densities, E. nostras larvae preferred to build their pits in the fractions with low densities (i.e., 121, 353 and 512 g/l) and only a small proportion constructed pits in high density fractions (i.e., 1312 and 1546 g/l). A complementary no-choice experiment demonstrated that pit diameter, pit depth and pit angle were negatively correlated with substrate density. These reductions in pit size can negatively affect prey capture success.

The evidence on the degradation processes in the midgut epithelial cells of the larval antlion Euroleon nostras (Geoffroy in Fourcroy, 1785) (Myrmeleontidae, Neuroptera)

We analysed structural differences between midgut epithelial cells of fed instar antlions’ larvae Euroleon nostras and starved ones. In starved larvae the presence of autophagolysosome-like structures was observed, which are characteristic structures associated with autophagy. The results presented here provide insight supporting the role of autophagy as a cell survival mechanism for the periods of food deprivation. Additional structural changes in the cytoplasm were seen in the spherites. The ultrastructure and chemical composition of spherites in the midgut epithelial cells of first, second and third instar larvae were observed with light microscopy and transmission electron microscopy (TEM). A detailed characterization of the elemental composition of the spherites was studied using analytical electron microscopy; a combination of energy dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS) and energy filtering TEM (EFTEM) was applied. The structure and elemental composition of the spherites changed during the period of larval life. Moreover, changes in chemical composition were found between spherites from fed and starved E. nostras. In fed first instar larvae, the spherites contained an organic matrix, composed of C, N and O. In this matrix, P, Cl, Ca and Fe were detected. In starved first instar larvae, only C, N and P were present. The spherites of fed second instar larvae were rich in organic and inorganic elements and were composed of C, N, O, Na, Mg, P, S, Cl, K, Ca, Mn, Fe and Zn. In starved second instar larvae, the chemical elements N, O, P, Ca and Fe were found. In fed third instar larvae, the spherites contained C, N, O, Na, Mg, P, Cl, K, Ca, Mn, Fe, Co and Zn. In starved third larvae, C, O, Si, Ca, and Fe were detected. Generally, the spherites are exploited in starved larvae. These results suggest that the elemental supply of spherites may provide crucial support for physiological processes during starvation periods amongst E. nostras instar larvae. In some cases in fed second and fed third instar larvae, spherites were seen in the lumen of the midgut. Such spherites could serve as reservoirs for nontoxic waste material that cannot be metabolized.

Application of analytical electron microscopic methods to investigate the function of spherites in the midgut of the larval antlion Euroleon nostras (Neuroptera: Myrmeleontidae)

This study presents an application of analytical electron microscopy in biology to investigate the chemical composition of the spherites and to elucidate the importance of these methods in the life sciences. The structure of the spherites in the midgut cells of first, second, and third instar larvae Euroleon nostras was investigated by a combination of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), electron energy-loss spectroscopy (EELS), and energy filtering TEM (EFTEM). The structure and chemical composition of the spherites changed during the metamorphosis. In first larvae, the spherites are composed of amorphous, flocculent material, containing C, N, and O. In second larvae and third ones, the spherites have concentric layers of alternating electron-dense and electron-lucent material. In second larvae, Si, P, Ca, and Fe are accumulated in the spherite organic matrix, composed of C, N, and O. In the spherites of third larvae, additionally Al was found. Therefore, the spherites are thought to store organic compounds in all three larval stages of E. nostras and additionally inorganic compounds in second and third ones. In first larvae, spherites are present in the midgut cells; in second and third larvae, they are present in the cells of the midgut and in its lumen. It could be suggested that the spherites might be involved in the regulation of the appropriate mineral composition of the internal environment and could serve as the accumulation site of nontoxic waste materials that cannot be metabolized.

Substrate particle size-preference of wormlion Vermileo vermileo (Diptera: Vermileonidae) larvae and their interaction with antlions

Wormlion larvae are found in substrates consisting of fine sand or powder, implying that they may be able to distinguish between different substrates according to particle size. To estimate the effects of particle size on wormlions, the pit-building decision of the larvae of the wormlion Vermileo vermileo was observed in four substrates consisting of different sand fractions. Wormlion larvae prefer the finest sand fraction with particle size <= 230 µm. When wormlions (Vermileo vermileo) and antlions (Euroleon nostras) are placed in the same container with two different substrates, interspecific predation does not occur. In two-substrate choice tests larvae of the two species show opposite preferences for two substrates offered. While wormlion larvae readily build pits in the finest sand fraction (<= 230 µm), antlion larvae prefer coarser sand (with particle size 230-540 µm). Wormlion preference for the finest sands and powders, and antlion preference for sands of medium particle size was confirmed by field observations. Sand particle size affects the spatial distribution of sand-dwelling insect larvae and thus may reduce conflicts between heterospecifics.

Orientation of the pit-building antlion larva Euroleon (Neuroptera, Myrmeleontidae) to the direction of substrate vibrations caused by prey

Pit-building antlion Euroleon nostras constructs efficient traps in sand to catch its prey. The predator is known to react to substrate vibrations produced by movements of its prey outside the pit with sand-tossing behaviour but it has not yet been ascertained if this reaction is directed towards the prey. The accuracy of the sand-tossing response in the presence of four prey species was measured using a video recording method. The sand-tossing angle was highly positively correlated with the prey angle. Sand tossing was most frequently elicited when prey was on the posterior sand surface. Covering the larval photoreceptors did not influence the antlion's localizing behaviour.

Sand as a medium for transmission of vibratory signals of prey in antlions Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract European pit‐building antlions (Euroleon nostras/ Geoffroy in Fourcroy/) detect their prey by sensing the vibrations that prey generate during locomotory activity. The behavioural reactions and some of the physical properties of substrate vibrations in sand are measured to observe signal transmission through the substrate. The frequency range of the signals of four arthropod species (Tenebrio molitor, Pyrrhocoris apterus, Formica sp. and Trachelipus rathkei) is 0.1–4.5 kHz and acceleration values are in the range 400 μm s−2 to 1.5 mm s−2. Substrate particle size and the frequency of prey signals both influence the propagation properties of vibratory signals. The damping coefficient at a frequency 300 Hz varies from 0.26 to 2.61 dB cm−1 and is inversely proportional to the size of the sand particle. The damping coefficient is positively correlated with the frequency of the pulses. Vibrations in finer sand are attenuated more strongly than in coarser sand and, consequently, an antlion detects its prey only at a short distance. The reaction distance is defined as the distance of the prey from the centre of the pit when the antlion begins tossing sand as a reaction to the presence of prey. The mean reaction distance is 3.3 cm in the finest sand (particle size ≤ 0.23 mm) and 12.3 cm in coarser sand (particle size 1–1.54 mm). The most convenient sands for prey detection are considered to be medium particle‐sized sands.

Pit building ant-lion larvae effect to the distribution of the substrate particles in their microhabitats

The distribution of the size of the substrate particles in and around the pits of the pit-building antlion larvae was examined at two different types of microhabitats (open and protected). Samples of substrate were taken from the side of the pits, from the edges of the pits and from 3 cm and 10 cm away from the edges of the pit. The size of the substrate particles taken 10 cm away from the edge is considered to be characteristic for the microhabitat. The samplings consisted of different quality of substrates such as sand, loess, clay and they were taken at all three larvae stages. The samples were divided into fractions by a sieve series and the distribution of the weight percentage of the granulation was analyzed. In order to compare the samples the cluster analysis and statistical tests were used. The preference calculations were performed with Ivlev's index of preference (Ei minimum -1; Ei maximum +1). In this respect the distribution of sandy area in the Carpathian Basin is in correspondence with the distribution of the pit-building ant-lion larvae living in open habitats. The preference of the ant-lion larvae living in protected habitat does not depend on the bedrock. The investigation proved that the substrate has particular spatial distribution in the pits and their environment (microhabitat). While building and repairing the pit, the larvae gather the fine particles in the pit and throw the bigger particles further out from the pit. The spatial distribution of the particle size of the substrate can be actively influenced by the chitin bristles and teeth of the mandibles and head of the larvae. Statistical analysis has proved that the particle size preference does not depend on the development stage of the larvae, it is not species dependent and it does not depend on the quality of the substrate as well. The preferred particle size of the pit-building ant-lion larvae was determined by the physical characteristics (particle size, to what extent they were cemented) of the substrate (sand, loess, clay) which is typical of the habitat. The present and the earlier studies suggest that Euroleon nostras, and very likely other pit-building species living in protected microhabitat, chose their habitats providing less food besides optimal particle size and thermal conditions. On the other hand, the species occurring in open habitats such as Myrmeleon bore, live in habitats with bigger food supply but with extreme thermal conditions and coarser particle size.