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.     

Variation in pit size of antlion (Myrmeleon carolinus) larvae: the importance of pit construction

Abstract.Larvae of several antlions build pits that vary in size across and within species. The influence of food limitation and pit building experience on variation in pit size of the larvae of Myrmeleon carolinus was investigated in the laboratory. Unfed larvae that were allowed to build pits had smaller pit diameters than fed larvae. However, fed antlions that had been previously prevented from pit building, initially did not build larger pits than unfed antlion larvae that, too, had been prevented from pit building. Therefore, physiological constraints associated with food limitation alone are not sufficient to explain the reduction in pit size of food limited antlions of this species.     

Thermal dependence of trap building in predatory antlion larvae (Neuroptera: Myrmeleontidae)

Trap-building predators remain under strong selection from thermal microenvironments. To address how soil temperature and body size affect trap building, we conducted a laboratory experiment using larvae of the antlion Myrmeleon bore at six ecologically relevant temperatures. Larger larvae built larger traps, and warmer soil led to more and larger traps. Body mass did not alter the dependence of trap building on temperature. Our results suggest that the physiological capacity of antlion larvae, which is affected by larval size and body temperature, is the major determinant of trap building. This effect should be considered when assessing interactions between antlions and prey.     

Utilisation of prey by antlion larvae (Neuroptera: Myrmeleontidae) in terms of energy and nutrients

Prey utilisation at low prey densities was determined for third instar Cueta sp., Furgella intermedia (Markl) and Palpares annulatus (Stitz) larvae in terms of wet weight, dry weight, energy and nutrients. Prey utilisation was similar to other insects on a wet weight (42-47%), dry weight (46-49%), energetic (40-58%) and nutritive basis (62-79%). Lipids (33-36%) provided energetically the highest contribution of the nutrients ingested. The quantities of water, proteins, nucleic acids, lipids and carbohydrates extracted by the antlion larvae were in proportion to their availability in their prey, the Hodotermes mossambicus larvae. The quantities of nutrients extracted by the antlion larvae at low prey densities were not significantly influenced by the differences in mandible size, antlion body weight or the trapping method (building a pit or not) of the antlion species. It is proposed that a low metabolic rate and the accumulation of fat reserves, and not the extent of prey utilisation, enable P. annulatus larvae to tolerate a 123-d starvation period in which 22.3% of their body weight is lost.     

Aspects of excretion of antlion larvae (Neuroptera: myrmeleontidae) during feeding and non-feeding periods

The main nitrogenous excretory products were determined for third instar Cueta sp. and Furgella intermedia larvae during periods of food abundance and for F. intermedia during starvation periods. Biochemical analysis indicated that allantoin was the main nitrogenous excretory product, with smaller quantities of ammonia, urea and uric acid. Respectively 9 and 13amino acids of low concentrations (0.005-0.329g/l) were detected by high pressure liquid chromatography in the excreta of Cueta sp. and F. intermedia larvae. The volume of urine produced and concentrations of the nitrogenous excretory products of fed Cueta sp. and fed F. intermedia larvae did not differ. F. intermedia excreted smaller volumes of urine and smaller quantities of nitrogenous excretory products during starvation than during periods of food abundance. Feeding conditions rather than the pitbuilding or non-pitbuilding lifestyles seem to be the major influence on the excretory products of these antlion larvae.     

Insecticidal bacteria isolated from predatory larvae of the antlion species Myrmeleon bore (Neuroptera: Myrmeleontidae)

Various bacterial species were isolated from the crop (digestive organ) of the antlion species Myrmeleon bore and tested for their insecticidal activity against caterpillars by injection. Sixty-eight isolates from the antlion crop were grouped into twenty-four species based on homologies of 16S rRNA gene sequences and biochemical properties. Isolated Bacillus cereus, Bacillus sphaericus, Morganella morganii, Serratia marcescens and a Klebsiella species killed 80% or more cutworms when injected at a dose of 5x10(5)cells per insect. In addition, cutworms killed by these isolates resembled observations made of caterpillars attacked by antlions. A culture-independent analysis showed that the isolated bacterial species are likely to be frequently present in the antlion crop. These results suggest that insecticidal microorganisms associate with antlions, and may promote the death of prey.     

Notes on the New Zealand antlion,Weeleus acutus (Neuroptera)

Abstract

The New Zealand antlion, Weeleus acutus (Walker), is redescribed and its relationships are discussed. Notes on the larva are given.     

Effect of spatial pattern and microhabitat on pit construction and relocation in Myrmeleon hyalinus (Neuroptera: Myrmeleontidae) larvae

Abstract.  1. In two sets of enclosure experiments, we studied the spatial pattern, relocation rates, pit construction rates, and microhabitat preference of Myrmeleon hyalinus larvae.
2. We showed that M. hyalinus larvae actively prefer shady sites and often relocate to shady areas when exposed to the sun. This behaviour may constitute a life-saving strategy in desert environments.
3. The initial spatial pattern in a cluster of antlion larvae did not affect the final pattern, relocation rate, or the pathway moved while relocating. We interpret this finding to mean that the spatial pattern of M. hyalinus larvae is mainly influenced by factors operating at large time-scales, such as exploitation competition and physical-microclimatological constraints, rather than those operating at shorter time-scales, such as interference competition.
4. In contrast, the likelihood of pit construction was positively correlated with nearest neighbour distance, possibly as a result of interference competition.
5. Pit construction rates were constant throughout the experiment, while relocation rates decreased with time.
6. Contrary to previous studies, we found no correlation between body mass and spatial position inside the cluster, suggesting that these differences are the products of slower processes (e.g. exploitation and body condition).     

Comparative study on the behavioral response to starvation in three species of antlion larvae (Neuroptera: Myrmeleontidae)

To clarify how pit-building antlion larvae behave during prolonged periods of low resource abundance, pit relocation rate, giving-up time, and respiration rate under starvation conditions were examined, using three species of antlion larvae. Most larvae ofMyrmeleon bore never relocated their pits before they starved to death, while larvae ofHagenomyia micans relocated more often thanMyrmeleon formicarius (average number of pit relocations 0.04 forM. bore, 0.19 forM. formicarius, and 0.62/individual/10 days forH. micans). The relative respiration rate, a ratio of respiration rate at starvation to that at satiation, was lower inM. bore andM. formicarius than in H. micans. Thus, there was an inversely proportional relationship between the pit relocation rate and the decrease in respiration rate under starvation conditions in the three species of antlion larvae.     

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.     

Seasonal regulation of dormancy in Chrysopa carnea (Neuroptera)

In Ithaca, New York, diapause incidence in Chrysopa carnea exceeds 50 per cent among adults emerging between 31 August and 3 September. Apparently, decreasing late summer day lengths, which exceed the stationary critical photoperiod in the laboratory, act on the sensitive stages and induce diapause. Full diapause intensity occurs about 2 weeks after adult emergence; complete winter coloration appears approximately 2 weeks later. Photoperiodic stimili in combination with the geographic strain largely determine diapause depth.Decreasing autumn day lengths decelerate diapause development and maintain diapause until the winter solstice. Subsequently, short day lengths and cold temperatures slow diapause development. In nature, neither long days, increasing day lengths, nor chilling hasten diapause termination. Diapause duration is largely determined by the interaction between inducing photoperiod, maintaining photoperiodic and thermal stimuli, and geographic strain. In Ithaca, diapause ends (all response to photoperiod ceases) between 22 January and 12 March.After diapause ends, the animals retain their diapause characteristics until temperatures exceed 4°C. Post-diapause reproductive development in females requires approximately 100 heat units above 4°C; however, below 8°C mating and oviposition are absent. Although the winter coloration remains, mating occurs within 1 day after transfer from 4 to 24°C. Temperature determines the rate at which the green summer colour returns.     

Sub-optimal pit construction in predatory ant lion larvae (Myrmeleon sp.)

The impacts on energy gains of two aspects of ant lion pit architecture were investigated in a natural population of pit-building ant lion larvae (Myrmeleon sp.) in Costa Rica. Field and laboratory settings were used to examine the impacts of circumference and depth of the pit on net energy gain rate. An optimization model predicted a point optimum circumference and angle of depression in an unconstrained system, and positive correlations between body mass, pit circumference, and pit angle of depression in the presence of physiological constraints on both measures. Such a physiological constraint is possible in this system due to a large one-time construction cost. All of these correlations were observed in a lab setting with filtered substrate and no competition; though none were significant in the field. Individuals additionally constructed wider, shallower pits in the field. These results are consistent with an angle of depression that is limited by the angle of repose of the substrate in the field, rather than physiology. These results provided suggestive evidence for sub-optimal pit dimensions in Myrmeleon sp., and for the importance of substrate type in understanding the architecture of natural ant lion pits. The model predicted that the frequency of relocation would not affect the optimal angle of depression, but it would affect the optimal pit circumference to a degree proportional to the square root of the change in the average time an ant lion occupies a single pit. These findings challenge the widely held assumption of adaptive optimality in animal foraging.     

Neotropical Osmylidae larvae (Insecta,Neuroptera): description of habitats and morphology

ABSTRACT

The larval stages of the genus Kempynus Navás, 1912 Navás, L. (1912), ‘Insectos neurópteros nuevos o poco conocidos’, Memorias de la Real Academia de Ciencias y Artes de Barcelona, 10, 135–202. [Google Scholar] (probably K. falcatus Navás, 1912 Navás, L. (1912), ‘Insectos neurópteros nuevos o poco conocidos’, Memorias de la Real Academia de Ciencias y Artes de Barcelona, 10, 135–202. [Google Scholar] based on the presence of synchronic and sympatric adults) are described for the Neotropical Region for the first time, and the larval stages of Isostenosmylus pulverulentus (Gerstaecker, 1893 Gerstaecker, C.E.A. (1893), ‘Ueber neue und weniger gekannte Neuropteren aus der familie Megaloptera Burm’, Mitt[h]eilungen aus dem Naturwissenschaftlichen Verein für Neu-Vorpommern und Rugen, 25, 93–173. [Google Scholar]) are redescribed. The external morphology of third-instar larvae of both species and their habitats are described and compared. Kempynus sp. is a water-dependent species and can be considered semi-aquatic, whereas I. pulverulentus larvae are terrestrial and live in undergrowth vegetation. The first key to identification of Neotropical Osmylidae larvae is provided, based on third-instar larvae of both species.     

Predation by bluegill sunfish (Lepomis macrochirus rafinesque) upon mealworm larvae (Tenebrio molitor)

Eleven responses comprise behaviour of bluegill sunfish (Lepomis macrochirus Rafinesque) preying upon mealworm larvae of Tenebrio molitor. Since each response could be repeated during an attack, behaviour can become quite complex in terms of total number of components comprising a predatory chain. When sunfish attacked the first prey of feeding sessions, predatory sequences contained an average of 8·0 components. Sequences dealing with the second and with all subsequent prey averaged 9·5 and 12·4 components respectively. Increased sequence complexity with increasing satiety depended upon increases in the frequencies of orienting and approaching prey as well as stopping and turning away from prey. Accordingly, satiety is hypothesized to produce more selective responsiveness to prey rather than simple diminution of feeding behaviour.     

Histopathology of Aedes aegypti (Diptera: Culicidae) larvae parasitized by Reesimermis nielseni (Nematoda: Mermithidae)

Histological observations were made of Aedes aegypti larvae parasitized for 2, 4, and 6 days by Reesimermis nielseni. Little difference was detected between the tissues of uninfected and nematode-parasitized larvae 4 days after infection, at which time most hosts were in the early fourth instar and their fat bodies were well developed containing abundant storage materials. Nematodes grew most rapidly between day 4 and day 6 of parasitism, depleting host metabolites, reducing the fat body and other host storage tissues while accumulating storage material in their trophosomes. Development of host imaginal discs was inhibited during this period. The severity of the nematodes upon host tissues depended upon intensity of infection. Dry weight measurements of nematode and host supported histological observations that the nematode developed most rapidly 4–6 days post-infection, thus causing most serious effects upon the host at that time.     

Comparative study of sensilla and other tegumentary structures of Myrmeleontidae larvae (Insecta,Neuroptera)

Antlion larvae have a complex tegumentary sensorial equipment. The sensilla and other kinds of larval tegumentary structures have been studied in 29 species of 18 genera within family Myrmeleontidae, all of them with certain degree of psammophilous lifestyle. The adaptations for such lifestyle are probably related to the evolutionary success of this lineage within Neuroptera. We identified eight types of sensory structures, six types of sensilla (excluding typical long bristles) and two other specialized tegumentary structures. Both sensilla and other types of structures that have been observed using scanning electron microscopy show similar patterns in terms of occurrence and density in all the studied species (with few exceptions). The sensilla identified are: coeloconica, placoidea, basiconica, trichodea type I, trichodea type II, and campaniformia. All these sensilla have mechano- or chemosensorial functions. Some regions of the larval body have been studied using SEM for the first time, such as the surface of the food canal, which bears sensilla coeloconica, and the abdominal segment X, that bears three types of sensilla: coeloconica, basiconica, and campaniformia. Sensilla placodea are newly reported on antlion larvae, being present on the mandibular base, pronotum, mentum, and cardum. Also, new locations of sensilla coeloconica (e.g., on rastra) and sensilla campaniformia (e.g., on odontoid processes) are noted. A novel porous texture with chemoreceptor function has been identified in the base of mandibles. A mechanism of dentate-notched surfaces that anchor maxillae and mandible, reinforcing the food canal, is detailed. All these sensorial structures, in addition to ocular tubercles for light caption and their great muscular system, confer to these larvae an extraordinary predation capacity to success hunting and living in such harsh environments.     

Aggregation,interference and foraging by larvae of Plectrocnemia conspersa (Trichoptera: Polycentropodidae)

The predatory net-spinning caddis larva Plectrocnemia conspersa aggregates in patches of high density during most of the year. The behavioural basis of the aggregation depends on (a) the initial tendency to spin a net where prey have been captured and (b) the abandonment of sites where prey are not captured within a threshold time after a previous meal. There is a powerful behavioural mutual interference effect in laboratory experiments between larvae at densities similar to those in the field. Larvae contest ownership of nets and the outcome is determined mainly by body size, usually without injury to either contestant. The lack of an aggressive response in August may be due to this mutual interference or to aspects of environmental instability which make an optimal allocation of foraging effort between patches difficult to attain.     

Localization of soil dwelling scarab larvae by the black-backed magpie, Gymnorhina tibicen (Latham)

Black-backed magpies, Gymnorhina tibicen (Latham), were tested for their ability to localize their normal prey, soil dwelling scarab larvae, under a variety of experimental conditions. Olfactory and vibrotactile cues were found to be unimportant for localization. The bird was able to localize the larvae accurately by the sounds produced by their burrowing. Any movements on the surface of the substrate created by the activity of the larvae below could also be used for localization, though these cues are normally not available in the field.     

Effect of density on spatial distribution,pit formation and pit diameter of Myrmeleon acer Walker, (Neuroptera: Myrmeleontidae): patterns and processes

The effect of increasing population density on the formation of pits, their size and spatial distribution, and on levels of mortality was examined in the antlion Myrmeleon acer Walker. Antlions were kept at densities ranging from 0.4 to 12.8 individuals per 100 cm². The distribution of pits was regular or uniform across all densities, but antlions constructed proportionally fewer and smaller pits as density increased. Mortality through cannibalism was very low and only occurred at densities greater than five individuals per 100 cm². Antlions in artificially crowded situations frequently relocated their pits and when more space became available, individuals became more dispersed with time. Redistribution of this species results from active avoidance of other antlions and sand throwing associated with pit construction and maintenance, rather than any attempt to optimise prey capture per se.     

穴蚁蛉的自然种群动态

本文主要报道了穴蚁蛉 Myrmeleon(Morter) sagax(Walker)幼虫的野外自然种群数量动态。穴蚁蛉 1年发生 1代 ,在自然界其幼虫 3～ 5月份数量平稳略有下降 ,5、6月间数量迅速下降 ,6月初数量最少 ;7～ 9月份数量迅速上升 ,而后下降 ;新一代穴蚁蛉幼虫 (蚁狮 )在 6月份出现。其种群 ,秋季以 1龄幼虫数量为多 ,冬季主要以 2龄幼虫为主越冬 ,春季以 3龄蚁狮占优势。春季野外采集来的蚁狮 ,在每日光照 14小时、每周两饲 (每次饲 1头米蛾 Corcyra cephalonica成虫 )的条件下饲养 ,结果发现 ,采集回时处于 3龄期的蚁狮比自然界大约提前 1个月结茧化蛹和羽化 ;而采集回时处于 2龄期的蚁狮则和自然界中的情况基本一致。