Size selection of latex beads by blackfly larvae (Diptera: Simuliidae) in the laboratory

In laboratory experiments, blackfly larvae collected from a lake outlet, a woodland and a meadow stream were tested for size selection of latex beads of < Ito > 100 μm diameters. 3 suspensions of varying proportions for each size category were supplied to these blackfly larvae in common experiments. Comparisons between the size frequency distributions of particles supplied and the particle compositions in the larval guts showed intra- and interspecific differences and were quantified by calculating Jacobs' electivity index. In all species selection of larger particles increased with the larger larval instars. Although there was a positive selectivity of small particles in some cases, the ingested proportion of large particles increases volumes and biomasses of gut content and may be more important for larval growth than small particles.     

白纹伊蚊幼虫龄期的发育历期

在实验室内20±1℃, 23±1℃, 25±1℃, 28±1℃和30±1℃恒温条件下, 观察了白纹伊蚊(Aedes albopictus)幼虫(广州株)的发育历期.幼虫的总发育历期和各龄幼虫的发育历期随温度的上升而缩短, 各龄幼虫历期在总发育历期中占有恒定的百分比, 据此计算出其捕获机率.各龄幼虫的发育历期与温度呈直线回归关系.通过积温公式, 求出各龄幼虫的积温常数.此外还探索了营养对幼虫发育历期的影响, 从而影响各龄幼虫捕获机率的计算.     

Diel drift of Chironomidae larvae in a pristine Idaho mountain stream

Simultaneous hourly net collections in a meadow and canyon reach of a mountain stream determined diel and spatial abundances of drifting Chironomidae larvae. Sixty-one taxa were identified to the lowest practical level, 52 in the meadow and 41 in the canyon. Orthocladiinae was the most abundant subfamily with 32 taxa and a 24 h mean density of 294 individuals 100 m⁻³ (meadow) and 26 taxa and a mean of 648 individuals 100 m⁻³ (canyon). Chironominae was the second most abundant subfamily. Nonchironomid invertebrates at both sites and total Chironomidae larvae (meadow) were predominantly night-drifting. Parakiefferiella and Psectrocladius were day-drifting (meadow) whereas 8 other chironomid taxa (meadow) and 2 taxa (canyon) were night-drifting. All others were aperiodic or too rare to test periodicity, Stempellinella cf brevis Edwards exhibited catastrophic drift in the canyon only. The different drift patterns between sites is attributed to greater loss of streambed habitat in the canyon compared to the meadow as streamflow decreased. Consequent crowding of chironomid larvae in the canyon caused catastrophic drift or interfered with drift periodicty. This study adds to knowledge of Chironomidae drift and shows influences on drift of hydrologic and geomorphic conditions.     

Immunocytochemical identification of prolactin cells in the pituitary gland of tilapia larvae (Oreochromis mossambicus: Teleostei)

Summary Using an antiserum to highly purified chum salmon prolactin, prolactin cells were identified in the putative rostral pars distalis of newly hatched tilapia larvae (Oreochromis mossambicus) by the immunogold method for the electron microscope. In the putative rostral pars distalis, some cells had another kind of secretory granule which was much less numerous, much smaller in size, and without immunoreactivity to salmon prolactin antiserum. Controls incubated with salmon prolactin-preabsorbed antiserum or normal serum showed no immunoreactive cells, confirming the specificity of the antiserum. The possible role of prolactin in the osmoregulation of tilapia larvae is discussed.     

环境因子对两种海洋双壳类幼体趋性行为中的调节作用

本文研究了温度、盐度和重金属等几种因子对缢蛏和长牡蛎幼体趋地性和趋光性行为的影响。结果表明:1)降低温度能增强缢蛏幼体的正趋地性,而长牡蛎幼体却由正趋地性转变为负趋地性,同时两种幼体的正趋光性受到抑制作用;升高温度对缢蛏幼体趋光性的影响不明显,但能加强牡蛎幼体的正趋光性。2)盐度提高时缢蛏幼体的正趋光性趋于增强,正趋地性趋于减弱。3)重金属Cu和Zn在各自的亚致死浓度下具有提高缢蛏幼体正趋地性和降低正趋光性的作用,而牡蛎幼体的正趋地性却趋于减弱,正趋光性趋于增强。本文据上述幼体的行为变化,还讨论了这几种因子对幼体垂直分布的调节作用。     

Swimming response of goldfish,Carassius auratus,and the tetra,Hemigrammus caudovittatus,larvae to individual food items and patches

Synopsis Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: handling pause (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched (area increased searching). Mean swimming speed was constant over a broad range (10¹–10³ ind·1^–1 of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches.     

Behaviour of drifting insect larvae

The larval drift behaviour of 23 species representing Ephemeroptera, Plecoptera and Trichoptera was investigated in the laboratory using different current regimes. Mayfly nymphs often performed swimming, while caddis larvae were reluctant to do so. Stonefly nymphs were intermediate. In mayflies swimming seemed to be used to reach the substrate as soon as possible. In contrast most stonefly nymphs by swimming prolonged the time spent in the water column. Modes of swimming and sinking posture differed markedly between the orders. Living passively sinking animals often reached bottom faster than dead control specimens, so consequently behaviour did not always express itself in activity. Some caddis larvae spun adherent anchor lines. Differences among taxa seemed more important in explaining swimming activity compared to preferred habitats (as stream, river and lake) in each species. However, observed differences among closely related species indicated subtle differences related to microhabitat to be of profound importance in explaining the alternative behavioural strategies used.     

Variation in larval black fly populations at three sites in a stream system over five years (Diptera:Simuliidae)

Five years of monthly samples taken from three sites in the Broad Cove River, two at lake outlets and one a kilometer downstream from an outlet were analyzed. Considerable variations in the population of each species between sites and years were observed. Fluctuations in the populations were not always consistent from site to site or between species at the same site from one year to the next. As all sites were on the same stream and within 3 km of each other with only slight altitude differences climatic factors were not a major factor producing variations observed between sites. Also the previous years population level did not appear to be directly related to the following seasons population level. Apparently localized conditions at a site were exerting a marked influence on the larval simuliid population at each site.     

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.     

Tentacle structure and feeding processes in life stages of the commercial sea cucumber Parastichopus californicus (Stimpson)

Tentacle structure and function in the pentacula larva, juvenile, and adult life stages of Parastichopus californiens (Stimpson) were examined via light and electron microscopy. Food particle adherance to the tentacle surface is mediated by an adhesive material in the case of the pentacula larva and additionally by mechanical entrapment in juvenile and adult animals. Mechanical entrapment is of secondary importance to adhesion during feeding.