Effects of spatio-temporal intervals between newly-hatched larvae on larval survival and development inMonochamus alternatus (Coleoptera: Cerambycidae)

The effects of distance between hatching larvae on survival and development were investigated inMonochamus alternatus. Two newly-hatched larvae were inoculated intoPinus densiflora bolts at a distance of 2.5 cm or 10 cm, simultaneously or at an interval of 2 weeks. Some larvae were inoculated singly as a control. When larvae were inoculated simultaneously, mortality of the closely-inoculated larvae was significantly higher than that of distantly-inoculated larvae. Such high mortality was identified as due to conspecific bites. When the two larvae were inoculated asynchronously, the first-inoculated larvae killed some second-inoculated larvae but were never killed by them. Consequently, mortality was higher in second-inoculated larvae than in first-inoculated larvae. In particular, there was a significant difference in mortality between them when the larvae had been inoculated closely. The mortality of second-inoculated larvae was higher in the closely-inoculated group than in the distantly-inoculated group although there was no significant difference between them. In the case of two simultaneously-inoculated larvae, the initial distance between them had no significant effect on the development and growth in the early larval stage. When the larvae were inoculated asynchronously, the first-inoculated larvae grew more quickly than singly-inoculated control larvae.     

Long-term movements of self-marked caddisfly larvae (Trichoptera: Sericostomatidae) in a California coastal mountain stream

1. Over 140 000 larvae of the case-building caddisfly Gumaga nigricula were self-marked as they incorporated glitter into small portions of their cases while reared in streamside troughs. These marked individuals were released into stream pools and their movements monitored in the dry season, when base flow was low and no spates occurred, and in the wet season when base flow was high and several spates occurred. 2. Of the 9,000–10 000 larvae released in each of two stream pools in the dry season, 4–20% (i.e. 377–1817 marked individuals) were observed on three sampling dates (4, 11 and 24 d after release). Most larvae (87–93%) remained within 4 m up- or downstream of the release line after 24 d. No larvae were found outside of the release pools, even after 37 d. 3. Of the > 120 000 larvae released in one stream pool near the beginning of the wet season, 408 larvae were recaptured 130–167 d later, a period that included 30 days of high flow associated with six spates. Estimated survivorship over this period was 0.7–6.2%; there was no relationship between survival and larval size at release. Most (75%) recaptured larvae were found in the pool where they were originally released. The remaining larvae were found downstream of the release pool. Larvae had generally dispersed only a short distance downstream of the release pool (median = 18 m, maximum = 222 m). In addition, four marked pupae were later found 436 m downstream of the release pool. 4. These results illustrate the sedentary nature of larval G. nigricula as well as the important role that high flow events play in larval mortality and dispersal. These case-building larvae move very little during low flow periods, even when food resources appear limiting. In contrast, the frequency and distance of larval dispersal are much greater during periods with high flow. 5. Our observations for G. nigricula support previously published inferences that larval dispersal within a stream can be limited for some aquatic insects. However, our observations also suggest that, even for a relatively sedentary species like G. nigricula, larval dispersal during periods with high flow may contribute significantly to gene flow within a stream reach.     

The Adhesive Organ of Larval Pike Esox Lucius L., (Pisces)

Newly hatched pike laryae swim by lateral movements of the trunk. The swimming path is directed upwards. They do not avoid obstacles but interrupt any movements immediately when colliding a substrate. Paired cement glands in rostro-nasal position excrete an elastic connection between larva and the touched substrate. Larvae spend yolk sac stage in a motionless position. The glands were studied by scanning electron microscope, by lightmicroscope and transmission electron microscope. The organs consist of two rostro-lateral areas which have a striking sculptured surface. The glandular cells are of the high prismatic type with basic nuclei and granulae in the apical parts. The granulae are already reduced in size and number after hatching against the prehatching stage. This indicates an early secretory activity before an attachement occured. There are grounds to consider mainly two ecological aspects in favour of pike larvae attached to substrates. One is the distance from the bottom water layers which are often characterized by oxygen deficiency and low water currents. Because pike larvae develop their gills later the gas exchange occurs with the body surface. Favourable water circulation normally exists in some distance from sediment and improves the respiration. The second aspect is governed by immobility and pigmentation which camouflage larvae against predators.     

Influence of Predator Presence and Prey Density on Behavior and Growth of Damselfly Larvae (Ischnura elegans) (Odonata: Zygoptera)

Foraging behavior is often determined by the conflicting benefits of energy gain and the risk of mortality from predation or other causes. Theory predicts that animals should have lower activity levels when either the risk of predation or the availability of resources in the environment is high. We investigated the adjustment of the behavior of I. elegans larvae to predator presence (Anax imperator) and prey density (Daphnia sp.) and their interaction in a completely crossed factorial experiment in the lab and the effect of behavior on growth. The foraging activity of the I. elegans larvae was significantly reduced in the presence of a free-swimming predator but not a caged predator. Abdominal movements were significantly reduced at a low prey density. Growth was significantly reduced by the presence of a free swimming predator and low prey densities. These results provide evidence that these damselfly larvae adjust their behavior to the presence of predators to increase their survival at the expense of reduced growth and development.     

Effects of structural habitat on drift distance and benthic settlement of the caddisfly,Ceratopsyche sparna

We conducted two experiments in flow-through, artificial streams to examine how habitat structure affected drift and benthic resettlement of larval hydropsychid caddisflies (Ceratopsyche sparna). In the first experiment, we quantified drift distance and the number of times larvae re-entered the drift in 9.0 × 0.51-m channels with contiguous patches (ea. 2.5-m long) of biofilm-covered gravel, biofilm-covered cobbles (– Cladophora), and Cladophora-covered cobbles (+ Cladophora). In the second experiment, we tracked nocturnal movements of larvae after benthic settlement in 2.8 × 0.1-m channels, each containing one of the three habitat types. In experiment 1, drift distance was (1) greatest in gravel and lowest in cobbles + Cladophora, (2) inversely related to hydraulic roughness of habitats, (3) independent of body size, and (4) similar for live and dead larvae. Average drift distance was relatively short (<2.5 m), regardless of habitat type. Number of drift re-entries also varied among habitats, being greatest in gravel and lowest in cobbles + Cladophora. No larvae re-entered the drift after settling in Cladophora patches. Results from experiment 2 revealed that drift propensities were higher for larvae in biofilm-covered gravel and cobbles than in cobbles + Cladophora. Larvae remaining in substrate patches (i.e. not drifting) laid fewer draglines in biofilm-covered stones than in Cladophora patches. Extent of benthic movement (i.e., crawling) by non-drifting larvae did not differ significantly among habitats. However, distance moved did differ with flow direction, being 4× greater downstream than upstream. These results highlight how local substrate and hydraulic conditions interact to affect small-scale movements of caddisfly larvae.     

The effect of invertebrate and vertebrate predators on the foraging movements of Ischnura elegans larvae (Odonata: Zygoptera)

SUMMARY.

• 1 The foraging movements of late instar Ischnura elegans larvae were monitored in laboratory experiments to study the effects of predators on larval feeding behaviour.
• 2 Ischnura larvae are sit-atid-wait, or ambush, foragers, moving occasionally between perches in search of profitable feeding sites. Larval foraging movements, monitored at different densities of Daphnia prey, increased significantly when prey were absent.
• 3 In experiments without prey, larval movement was inhibited by the presence of fish predators, as well as by invertebrate predators (Notonecta glauca), but not by closely related, non-predatory invertebrates (Corixa punctata) or physical disturbance of the water (intermittent air bubbles).
• 4 Further experiments varied Ischnura hunger levels (0–8 days without food) and illumination (light or dark) with and without notonectid predators. Hunger had no consistent effect on penultimate instar behaviour but final instar foraging activity was significantly modified: movements increased after 4 days starvation and decreased again after 8 days. This response was suppressed by the presence of predators. Both larval instars moved significantly less often in the light, even when predators were absent.
• 5 These phenotypically flexible predator-avoidance responses are likely to decrease the risk of predation by both visual and tactile predators. However, predators clearly have an important influence on the feeding niche of Ischnura larvae, and may decrease the overall feeding efficiency, growth rate, and survival of larvae by constraining their movement in search of profitable feeding sites.

     

Behavioural,developmental and morphological responses of Chironomus gr. thummi larvae (Diptera,Nematocera) to aquatic pollution

Populations of Chironomus gr. thummi larvae from two differently polluted lowland streams (Dommei, high cadmium and zinc; Ijse, medium copper and organic xenobiotics) were screened for behavioural and morphological responses to pollution. Behaviours such as locomotion (swimming and looping), respiration movements (ventilation) and inactivity were quantified with impedance conversion technique. Chironomids from the Dommel were more active than larvae from Ijse. In Ijse, deformed larvae showed less emergence, less locomotion and more ventilation than non-deformed larvae. In Dommel, deformed and normal larvae were equally fit (behaviour, emergence).     

Field and laboratory observations on the substrates of the mushroom fungus gnat Lycoriella auripila (Diptera: Sciaridae)

The movements of Psila rosae larvae were studied under field and laboratory conditions. In the field, larvae moved up to 60 cm along and between carrot rows, although more larvae moved during the first generation than the second. Sudden increases in soil moisture, and not its prevailing level, stimulated the larvae to move from carrots into the soil surrounding the roots. Up to 50% of the larvae that left their mines in carrots following a sudden increase in soil moisture did not return to the same mine. Evacuation of mines by larvae appears to be a reflex response to the flooding of their mine and might be connected with the production of toxic conditions within the mine following flooding.     

Comparative swimming abilities of fed and starved larval largemouth bass (Micropterus salmoides)†

Sustained swimming abilities of fed and starved larval largemouth bass (Micropterus salmoides L.) were compared in the first week after swimming initiation. Fed larvae improved to a sustained velocity of 4·0 cm/sec while starved larvae attained a velocity of only 1·5 cm/sec. Swimming behaviour for fed and starved larvae was quantified for number of moves, average distance/move, and total distance for all moves in 1 min intervals. Fed larvae were always more active than starved larvae, although real differences did not appear until the 4th day after swimming initiation.     

Blackfly (Diptera: Simuliidae) abundance in a lake outlet: test of a predictive model

A mathematical model based on assumptions of proportionality of filter-feeding insect larvae and their food supply and of the ability of the larvae to substantially reduce the sestonic food supply was developed. The predictions of the model were tested by censusing simuliid blackfly larvae in the outlet stream of a mesotrophic lake. Observed trends in simuliid density agree closely with the predictions. Two seston components (diatoms, detritus) increase downstream contrary to prediction. Potential predators of simuliids were censumed. Isoperla spp. decreased with increasing distance below the lake while the perlid stoneflies Calineuria and Hesperoperla seemed to be excluded from the outfall region.     

Oviposition and larval dispersal of the common armyworm,Mythimna convecta (Walker) (Lepidoptera: Noctuidae)

The common armyworm, Mythimna convecta (Walker), is a pest of cereal crops and pasture grasses in Australia. During autumn, egglaying in grasslands commonly occurs before plant growth commences. The possible association between oviposition and dried grasses was investigated in field studies of larval distribution in a pasture and a crop habitat, and in laboratory studies of oviposition site preferences and the mode of dispersal of newly hatched first instar larvae. A comparison of a green grass pasture with and without a component of dried grass showed that highest densities of M. convecta larvea. were found in the former. In the laboratory, egg batches were laid between plant parts in close contact, such as between the stem and leaf axil and between seeds in the seed head. The crevices in dried plant material and seed-heads were significantly more acceptable for oviposition than in green foliage. Oviposition in dried plant material enables M. convecta to rapidly colonize ephemeral grasslands immediately after rains when the neonate larvae can disperse and feed on new vegetative growth. Shortly after hatching, 93% of first instar larvae used fine silken threads for aerial dispersal in 0.5 m s^-1 air currents and 43% were blown a distance of more than 1.0 m. In the field, sticky traps caught larvae dispersing in all directions from a central source, and indicated that approximately 30% were transported 2 m after 7 days of light to medium breezes. Terminal velocities of newly hatched larvae were 20–130 cm s^-1, depending on the length of the trailing thread.     

Studies on the horizontal migration of dipterous stem borers (Oscinella spp.) in direct drilled Italian ryegrass

The distance stem boring dipterous larvae e.g. Oscinella frit L. migrate in direct drilled Italian ryegrass (Lolium multiflorum) was investigated. First, adjacent contrasting swards of Italian ryegrass or Cocksfoot (Dactylis glomerata) were grown which were, respectively, expected to be either infected with large populations of larvae or likely to be free of larvae. Sampling revealed that these expectations were realised. Swards were then desiccated by herbicide, and subsequently direct drilled with Italian ryegrass. Over 50% of the larvae in original, infested part of the sward migrated to infest tillers of the newly sown ares. The distance larvae migrated was gauged by assessing how far they were found from the perimeter of a previously uninfested area which had been reseeded. Most larvae migrated 20 cm or less, but a small proportion appeared to migrate several metres, apparently passing many suitable host tillers as they did so.deceased September 1989     

Studies on production and food consumption by the larval simuliidae (Diptera) of a chalk stream

Summary Large populations of S. ornatum and S. equinum inhabit Ranunculus plants in the Bere Stream at Bere Heath. A weekly sampling programme obtained both larvae and pupae. The results of weekly sampling indicated four annual generations of S. ornatum and three of S. equinum. Quantitative samples of larvae, obtained at least three times in each generation gave estimates of production ranging from 0.26 g to 2.75 g dry weight m-² per generation of larvae of S. equinum and 0.15 g to 1.19 g dry weight m-² per generation of larvae of S. ornatum.Retention times of food by larvae, under field conditions were in the order of twenty to thirty minutes. Following determination of the weight of the gut contents for each size class of larvae, the activity of feeding larvae was calculated to achieve complete theoretical clearance of suspended material in a distance of 0.6 km, at peak population densities in the summer months.Dept. of Applied Biology, Bath University of Technology     

Substrate interstices as a habitat for larval Thraulus bellus (Ephemeroptera) in a temporary floodplain pond

• 1 Larvae of the ephemeropteran Thraulus bellus were sampled from the substrate interstices of a floodplain pond along the River Adour (south-west France). Quantitative sampling was carried out using traps arranged in five transects of four traps each, made up of five vertical compartments between +20 and -80cm from the surface of the substrate. The 100 compartments thus obtained were each 2.861 volume, and were sampled once a month from January 1988 to January 1989.
• 2 An influx of young larvae coming from the permanently flooded deep substrate invaded the upper 80cm of the substrate on and after mid-January. An increase in larval density and frequency of occurrence in the compartments occurred until May before emergence of the adults. A second colonization phase by young larvae took place from July to September, and was followed by reductions in larval density and frequency of occurrence during the autumn/winter drop in water level.
• 3 Horizontal and vertical movements of the larval population within the interstitial habitat of the pond were clearly linked to the water level fluctuations. However, differences between the five transects indicated a control of these movements by factors such as slope of the substratum, macrophytic vegetation, and the influence of springs. A relationship was found between population density and probability of submergence of the compartments, indicating that the larvae avoided locations most influenced by the fluctuating water levels.
• 4 The temporarily flooded substrate interstices appear to be a refuge for the larvae of T. bellus, preventing them from overlapping with two other abundant ephemeropterans, namely Cacnis horaria from silt habitats and Cloeon gr. simile from macrophyte beds.

     

Colonization of perspex strips by larvae of Austrosimulium bancrofti (Taylor) near Ipswich,Queensland

Larvae of the Taxon Austrosimulium bancrofti (Taylor) were collected from perspex strips placed in rapids of the Brisbane River during January (summer) and October (spring). Separation of larvae according to the mixture approach to clustering demonstrated that: a) October cluster I larvae were larger and underwent an additional cluster to those collected in January, b) there was an additional cluster of larvae in each month, which correlated with the percentage of A. bancrofti Ipswich B that were identified cytologically, and c) greater numbers of later cluster larvae were collected from the strips than early clusters.Multivariate analysis demonstrated that distance from the lip of the rapids, strip texture and water velocity had a significant effect on the number of larvae colonizing perspex strips. Numbers increased with: a) decreasing distance from the lip of the rapids, b) increasing surface area of roughened strips and c) water velocity in the range 1.00 < X 1.38ms^–1. The influence of adult female oviposition behaviour, larval behaviour, sampling time and technique are discussed in relation to the parameters that influenced the colonization of artificial substrates.     

The reaction of larvae of Simulium noelleri (Diptera) to different current velocities

Larvae of Simulium noelleri Friederichs aggregate at high population densities (more than 10² cm^–2) on sluices, dams, and spillways. Experiments were conducted in a laboratory trough to assess the reaction of larvae to different current velocities (velocities ranged from 5–49 cm s^–1). In the lower part of the range of water velocities used, larvae moved a greater distance upstream from where they had been located. Larger larvae always showed a greater tendency to move than did smaller larvae, whatever the velocity. This intraspecific variation in reaction to different current velocities allows the aggregation of larvae of mixed sizes at suitable sites, smaller individuals being occluded by those that are larger.     

Abiotic factors affecting the infectivity of Steinernema carpocapsae (Rhabditida: Steinernematidae) on larvae of Anastrepha obliqua (Diptera: Tephritidae)

The effects of soil depth, soil type and temperature on the activity of the nematode Steinernema carpocapsae (Filipjev) were examined using larvae of the West Indian fruit fly, Anastrepha obliqua (Macquart). Bioassays involved applying infective juveniles (IJs) to the surface of sterilized sand in PVC tubes previously inoculated with fly larvae of two ages. The 50% lethal concentration (LC₅₀) values estimated for 6-day-old larvae were 9, 20 and 102 IJs/cm² in tubes containing 2, 5 and 8 cm depth of sand, respectively, whereas for 8-day-old larvae, LC₅₀ values were 16, 40 and 157 IJs/cm², respectively. The effect of soil texture on the activity of S. carpocapsae was tested by applying the corresponding LC₅₀ concentrations of nematodes to sand, sand–clay and loamy–sand soils. For 6-day-old larvae, soil type had a highly significant effect on infection with the highest percentages of infection observed in the sand–clay mixture (60–82% depending on depth) compared to 45–64% infection in sand and 23–30% infection in loamy–sand soil. A very similar pattern was observed in 8-day-old larvae except that infection rates were significantly lower than in younger larvae. There was a significant interaction between soil type and soil depth. The effect of three temperatures (19, 25 and 30°C) on infection was examined in sand–clay soil. The infectivity of S. carpocapsae was affected by temperature and soil depth and by the interaction of these two factors. Response surface analysis applied to second order multiple linear regression models indicated that the optimal temperature for infection of larvae of both ages was ~26°C, at a depth of 7.9 cm for 6-day-old larvae and <2 cm for 8-day-old larvae, resulting in a predicted 91.4% infection of 6-day-old larvae and 61.2% infection of 8-day-old larvae. These results suggest that S. carpocapsae may have the potential to control fruit fly pests in tropical ecosystems with warm temperatures and high soil moisture levels, although this assertion requires field testing.     

Larval movement ofLasioderma serricorne (F.) (Coleoptera: Anobiidae) in a plane

The mean maximum change in position of larvae of Lasioderma serricorne (F.) at 30°C, 60% RH increased by 0.290 cm/day, their mean position at the end of a 24 hour period increased by 0.245 cm/day. The linear distance from the point of origin was equal to approximately one third of the total distance moved. Either density or high numbers increased the rate of movement.