Dušan Devetak

Substrate particle size affects pit building decision and pit size in the antlion larvae Euroleon nostras (Neuroptera: Myrmeleontidae)

Abstract.  The larvae of the antlion Euroleon nostras are pit‐builders, constructing pitfall traps in loose sand. The number of pits and the pit diameter are recorded when larvae are kept in substrates with different particle sizes. The most convenient pit‐building sand fractions are two fractions with fine sand (≤ 0.23 mm; 0.23–0.54 mm). The largest pits are constructed in sand with a particle size of 0.23–0.54 mm. In this sand fraction, larvae of all three instars most readily build pits. No pits are constructed in sand with a particle size greater than 1.54 mm. First‐ and second‐instar larvae avoid building pits in substrates of particle size 1–1.54 mm, but third‐instar larvae construct pits in this sand fraction. It is assumed that the antlion is capable of distinguishing between substrate types and this hypothesis is tested by giving larvae the choice of building a pit in one of four particle‐size fractions. Larvae of all three instars prefer to build pits in the fraction with a particle size of 0.23–0.54 mm. Only third‐instar larvae build pits in all four fractions, but only occasionally in the coarser fraction.

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.

Effects of larval antlions Euroleon nostras (Neuroptera, Myrmeleontidae) and their pits on the escape-time of ants

Abstract.  Pit‐building antlions are predators with a unique predation strategy, namely using pitfall traps constructed in loose sand to catch prey. Here, prey escape‐time in the field is measured by introducing ants into one of four different treatment arenas. The first treatment lacks pits and antlions, the second includes 10 antlions that did not build pits, the third comprises eight artificially constructed pits, and the fourth is a treatment of eight antlions in pits and two without pits. Their pits are of a similar size to those used in the third treatment. When antlions are present without constructing pits, they impede the dispersal of prey. The mean escape‐time for one half of the released ants is twice as long with antlions present as without them. When pits are present, the time taken for one half of the released ants to escape the predator is more than 10 times as long as when pits are absent. Escape‐time from artificial pits is three times that from nonpit building antlions. Pits hinder the escape of ants and therefore increase the amount of time that the prey is available for capture. In the area where the pits are occupied by antlions, escape‐time is four times longer than in a treatment with similar sized artificial pits. Thus, it appears that not only a pit, but also the presence of antlions influences the capture success.

The visual orientation strategies of Mantis religiosa and Empusa fasciata reflect differences in the structure of their visual surroundings

In the present study, peering behaviour, which is used to measure distance by the image motion caused by head movement, is examined in two types of mantid. Mantis religiosa inhabits a region of dense grass consisting of uniform, generally uniformly aligned, and closely spaced elements and executes slow, simple peering movements. In contrast, Empusa fasciata climbs about in open regions of shrubs and bushes which consist of irregular, variably aligned and variably spaced elements and it executes comparatively quick, complex peering movements. Hence, it seems that in these two species of mantid, the same orientation mechanism has been adapted to the unique structures of their visual surroundings. Apparently M. religiosa uses motion parallax and E. fasciata uses a combination of motion parallax and forward and backward movements (image expansion/contraction over time) to detect object distances.

Cold tolerance in terrestrial invertebrates inhabiting subterranean habitats

*tone.novak@uni-mb.si morphological adaptation and do not complete their life cycle there. 2) Troglophiles alternate between the epigean and hypogean habitats or live permanently in subterranean habitats; they show some moderate adaptation, such as partly reduced eyes and adaptations to compensate for the lack of visual orientation. Some among these do not complete their life cycle underground, while others do. 3) Troglobionts complete their life cycle in a hypogean environment, and most of them clearly show troglomorphic characteristics, like eyelessness and depigmentation. In contrast to the frequent preference for these three ecological groups, Novak et al. (2012) found that, on the one hand, trogloxenes and troglophiles together represent a group of variously adapted species, rather than two ecologically clearly separated categories, and, on the other hand, troglobionts divide into two strictly separated subgroups. Invertebrates are ectothermal and at their critical thermal minimum they enter chill-coma, where neuromuscular transmission and movement cease INTRODUCTION

Substrate vibration sensitivity of the leg scolopidial organs in the green lacewing, Chrysoperla carnea

Abstract The threshold sensitivity of the leg-vibration receptors of the green lacewing, Chrysoperla carnea, was investigated electro-physiologically. The legs were stimulated by sinusoidal vibrations. Summed responses from the leg nerve fibres of different legs do not differ much. In each leg there are two scolopidial organs which respond to vibration. The most sensitive—the subgenual organ—shows maximum sensitivity in the frequency range 1.5–2 kHz and a displacement threshold near 0.2 nm, corresponding to an acceleration of about 0.03 ms−2. The other is the femoral chordotonal organ with maximum sensitivity at about 1 kHz and the threshold between 0.1 and 1 ms−2. After ablation of both scolopidial organs, only responses of non-scolopidial organs persist, very probably campaniform sensilla.

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. Microsc. Res. Tech., 2011.

Effect of substrate temperature on behavioural plasticity in antlion larvae

Temperature is of crucial importance, affecting all aspects of insect life such as survival, development and daily activity patterns, and consequently behaviour. In the present study we evaluated the effect of temperature on the behavioural plasticity of antlion larvae, the sit-and-wait predators, which are considerably more dependent on local habitat conditions. We provided ethological descriptions of pit construction and feeding behaviour. An increase in temperature led to greater activity and consequently to greater frequency of sand tossing during pit construction. Larvae constructed bigger pits at higher temperatures, but required less time than at lower temperatures, when the resulting pits were the smallest. At low temperature, larvae required more time for feeding, and behaviour followed a core pattern with little variety, in comparison to behaviour at high temperatures. Two behavioural patterns occurred only at the highest temperature: ‘relocation’ and ‘submergence’, presumably in response to high temperatures.

Sand-Borne Vibrations in Prey Detection and Orientation of Antlions

Pit-building antlions capture their prey by digging funnel-shaped pits in loose sand and then laying in wait for prey to fall inside the trap. Behavioral experiments studying predator–prey interactions and measurements of vibrations propagated in sandy substrates revealed that antlions are extremely sensitive to substrate vibrations produced by prey crawling on the sand surface. Prey produce low-frequency sand-borne vibrations, and to locate a source of vibration, antlions rely on time differences of waveforms arriving at their receptors—tufts of hairs positioned on lateral parts of the mesothorax and metathorax. In this chapter, the role of physical properties of sand in substrate-borne vibration transmission is discussed.

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.