Winter Generation Research Articles

Patterns of variation in the dry body weight of Calanus finmarchicus in copepodite Stage V during autumn and winter in the Firth of Clyde

Variations in dry body weight in the Stage V copepodite, associated with the development of the winter generation of Calanus finmarchicus (Gunnerus) in the Firth of Clyde each year were observed from 1978 to 1982, during early October and the middle of January.The Stage V copepodite was dimorphic with respect to body size. Body weights of freeze-dried specimens were measured and form was distinguished using the prosome length. Allometric relationships of the dry weight to length in the two forms were similar, and stable between autumn and winter. From the mean of estimates for all collections, dry body weights of individual Stage V copepodites were proportional to the cube, approximately, of prosome lengths. Proportional coefficients were seasonally variable, but on all occasions these were greater for the large than the small form. Variations in dry weight were directly associated with the distinction between forms in body volume.Collections from October and January encompassed the period between the end of maximal Copepodite V recruitment and the onset of adult recruitment to the winter generation. Over this period, however, the dry body weight in all years decreased relative to length in Copepodite Stage V. This decrease, on average, was by 17% and 23% in the large and small forms respectively. Monthly collections from one population were used to examine these patterns in relation to the development of gonads. Stage V copepodites of both forms were increasing in dry weight during October, but from November were losing weight continuously. Maturation in the majority of these individuals was restrained throughout autumn, abruptly accelerating in winter.

Ecological observations and life histories of five net‐spinning caddisflies (Trichoptera) of the lower ardèche river

Four species of the family Hydropsychidae (Trichoptera) and one species of Philopotamidae (Trichoptera) which coexist in the lower reaches of the Ardeche River (France), from Ruoms to St‐Martin‐d'Ardeche, were studied from July 1982 to December 1984. In order of decreasing importance they are: (52.4%) Hydropsyche exocellata Dufour, (31.7%) Cheumat‐opsyche lepida (Pictet), (8.6%) Hydropsyche pellucidula (Curtis), (6.2%) Chimarra marginata (L.), (1.0%) Hydropsyche siltalai Dohler. These proportions agree with the downstream location of the study area, which is in the epipotamon. The populations of H. exocellata and Che. lepida sampled upstream and in the canyon from March to December 1984 had bivoltine developments cycles, whereas Chi. marginata the only Philopotamidae found on the Lower Ardeche River, had a univoltine cycle. Development of the Che. lepida winter generation was somewhat faster than that of H. exocellata whereas the summer generation developed more slowly than that of H. exocellata. Being mo...

Spatial and temporal patterns of predation by ants on eggs of Cactoblastis cactorum

ABSTRACT. Predation of Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) eggs by ants was studied for a summer and a winter generation on prickly pear Opuntia ficus‐indica (L.) Miller plants in the field. Egg Predation between plants was spatially density‐dependent in the winter but not in the summer generation. To test for the presence of delayed density‐dependent mortality within generations, percentage egg Predation during 5‐day periods was plotted against the number of eggs available in each period. Data points joined in a time sequence moved in an anticlockwise direction in the summer generation, suggesting a delayed density‐dependent response by the ants, whereas in the winter generation the points moved in a clockwise direction. The degree of coincidence of the C. cactorum eggs with the peak larval production periods of the ants is suggested as the main reason for the temporal changes in egg Predation.

Studies on the life cycle and reproduction of the parasitic amphipodHyperia galba in the North Sea

The structure of aHyperia galba population, and its seasonal fluctuations were studied in the waters of the German Bight around the island of Helgoland over a period of two years (1984 and 1985). A distinct seasonal periodicity in the distribution pattern of this amphipod was recorded. During summer, when its hosts—the scyphomedusaeAurelia aurita, Chrysaora hysoscella, Rhizostoma pulmo, Cyanea capillata andCyanea lamarckii—occur in large numbers, supplying shelter and food, a population explosion ofH. galba can be observed. It is caused primarily by the relatively high fecundity ofH. galba which greatly exceeds that of other amphipods: a maximum of 456 eggs was observed. The postembryonic development is completed in the medusae infested; only then are the young able to swim and search for a new host. The smallest freely-swimming hyperians obtained from plankton samples were 2.6 mm in body size. The size classes observed as well as moult increment and moulting frequencies in relation to different temperatures suggest that two generations are developed per year: a rapidly growing generation in summer and a slower growing generation in winter that shifts to a benthic mode of life and hibernation. For short periods, adult hyperians may become attached to zooplankters other than scyphomedusae. However, when releasing the progeny, they are dependent on the presence of these coelenterates. Apparently, a host specificity does not exist. During daytime, the hyperians seem to avoid a host change; only 0.2% of all the individuals sampled in the plankton during the day were not associated with medusae. The heavy infestation of medusae by this crustacean leads to a weakening and a progressive breakdown of these important predators on fish larvae.H. galba occupies a specific position in the marine food web which is discussed in detail.

Comparative observations on the biometry and development of Calanus finmarchicus and C. helgolandicus in Copepodite Stage V, with comments on other Calanidae

A similar, sexual dimorphism in Copepodite Stage V was observed in winter generations of Calanus finmarchicus (Gunnerus) and C. helgolandicus (Claus), co-existing in the Firth of Clyde, Scotland. In both species, the frequency distribution of prosome length in the Copepodite V population was bimodal. Among individual Stage V copepodites kept in the laboratory, those of the larger form alone produced adult males. Indications of morphological distinctions between the forms other than in size, however, were absent. Differences in least-squares regressions of individual cephalosome on metasome lengths, previously attributed to a distinction in prosome shape by Grigg et al. (1985), reflected size alone. These two measurements also were greater in the “large” form, but this independently of each other. Variations in their relative contributions to the prosome length distinguished individuals, and were continuous between the forms. Present and previously published observations on members of the family Calanidae have been compared. The presence, or not, of a sexual distinction in prosome length in the Stage V copepodite is variable among calanids, within and between species. A possible association with the extent of seasonal variations in size and life-cycle characteristics is suggested.

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The reproduction of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, was studied in winter and spring 1978, under various temperature and salinity conditions, using Chlorella sp. and Amphidinium sp. as food. Maximum numbers of successive eggs sacs (9), eggs per sac (39.3) and total egg production per female (311) were recorded for the witner generation, only 4.8, 34.8 and 109, respectively, for the spring generation. In contrast, the number of eggs per female per day was highest (11.3) in the spring generation, which displayed a more rapid reproductive cycle. Despite strong individual variations in the rhythm of egg sac production and in abundance of eggs per sac, egg production was generally higher during the first third of adult life, attaining a maximum after production of the second or the third egg sac. The continuous presence of the males was necessary to assure complete fertilization of eggs throughout the whole life of adult females. Hatching rate displayed high individual variability, in particular for the spring generation, which had lower average hatching rates (between 0 and 26%, depending on salinity or temperature) than the winter generation (14 to 64%). These differences may be related to the ability of E. velox to produce resting eggs during spring, allowing the species to maintain itself in a temporary water milieu. Temperature significantly affected longevity and daily egg production of females; presence or absence of males did not affect these parameters. An increase in salinity from 20 to 30%. reduced longevity, number of egg sacs, and daily egg production in the winter generation, but not in the spring generation. The specific daily production of females during their adult life was calculated from the egg production:biomass ratio of females, in carbon units. In the winter generation, this ratio increased between 10° and 15°C compared to ratios between 15° and 20°C; the opposite was observed for the spring generation. The seasonal differences in the effects of temperature and salinity on reproduction could indicate an adaptation mechanism to the strongly thermal and haline seasonal fluctuations which characterize the habitat of Ex. velox (brackish waters, drying-up in summer). Larval mortality was high, except at 20%. S for the spring generation. The sex-ratio of the offspring was unaffected by variations in breeding conditions. Hatching time and development time of larvae could be described by two Bělehradek equations displaying close b and (α) coefficients. We calculated the energy balance of adult females from data obtained in a previous study on feeding and respiration in E. velox, and this is discussed in context with the egg production results. Net growth efficiency varied with algal concentration according to an asymptotic curve, reaching a maximum of 0.43 with Tetraselmis maculata as food or 0.53 with Amphidinium sp. Actual egg production rate obtained in the present study was in good agreement with that calculated by the difference between assimilated food and respiration expenses.

Density, Biomass, and Production of Chironomidae (Diptera) in Lake Kasumigaura during 1982-1986

Seasonal changes in the density and biomass of chironomid larvae were studied at 10 locations in Lake Kasumigaura for 4 yr from March 1982-April 1986. Tokunagayusurika akamusi and Chironomus plumosus were dominant at all stations. Clinotanypus sugiyamai was abundant at the centers of Tsuchiurairi and Takahamairi Bays as well as the center of the lake. On the contrary, Procladius culiciformis was distributed mainly at the innermost part of Takahamairi Bay. Larvae of Dicrotendipes sp., Glyptotendipes sp., Microchironomus sp., Polypedilum sp., and Stictochironomus sp. were also recovered from Takahamairi Bay and/or Tsuchiurairi Bay. Density of T. akamusi increased every 2 yr synchronously at all stations except for innermost-bay stations. Although this species emerges every autumn, many of the individuals presumably have 2-yr life cycle. There were three generations per year for C. plumosus, three for C. sugiyamai, and at least two for P. culici formis. C. plumosus density just before the emergence was lower for the summer generation than the winter generation. This was presumably due to the progressive eutrophication of Lake Kasumigaura. Chironomid production was extremely high during the winter. The annual production averaged for 10 stations and for 4 yr was 3.7 g dry weight·m-2·yr-1 for T. akamusi and 3.2 g dry weight·m-2·yr-1 for C. plumosus, 0.052 g dry weight·m-2·yr-1 for C. sugiyamai, and 0.006 g dry weight·m-2·yr-1 for P. culiciformis. Yet the values were underestimated for T. akamusi and C. plumosus. Annual production of both T. akamusi and C. plumosus increased from the innermost part of the bays towards their mouths or the lake outlet.

Sex-dependent composition of cuticular hydrocarbons of the colorado beetle, Leptinotarsa decemlineata say

1. 1. Qualitative and quantitative investigation of epicuticular and internal hydrocarbons of Colorado beetles of winter generation were performed. 2. 2. Quantitative compositional differences for sexes were found. 3. 3. Females contain more branched methylalkanes whose tentative structure was identified as either tetramethylhentriacontane or trimethyltritriacontane or a mixture of both. 4. 4. Compositional studies of potato leaves were also done. A prominent component of leaf waxes, 2-methyltricontane, was also found in cuticular hydrocarbons of both sexes as one of the most abundant compounds.

Photovoltaic-Electrolyzer System Transient Simulation Results

Brookhaven National Laboratory has developed a Hydrogen Technology Evaluation Center to illustrate advanced hydrogen technology. The first phase of this effort investigated the use of solar energy to produce hydrogen from water via photovoltaic-powered electrolysis. A coordinated program of system testing, computer simulation, and economic analysis has been adopted to characterize and optimize the photovoltaic-electrolyzer system. This paper presents the initial transient simulation results. Innovative features of the modeling include the use of real weather data, detailed hourly modeling of the thermal characteristics of the PV array and of system control strategies, and examination of systems over a wide range of power and voltage ratings. The transient simulation system TRNSYS was used, incorporating existing, modified or new component subroutines as required. For directly coupled systems, we found the PV array voltage which maximizes hydrogen production to be quite near the nominal electrolyzer voltage for a wide range of PV array powers. The array voltage which maximizes excess electricity production is slightly higher. The use of an ideal (100 percent efficient) maximum power tracking system provides only a six percent increase in annual hydrogen production. An examination of the effect of PV array tilt indicates, as expected, that annual hydrogen production is insensitive to tilt angle within ± 20 deg of latitude. Summer production greatly exceeds winter generation. Tilting the array, even to 90 deg, produces no significant increase in winter hydrogen production.

Leaf mines: their effect on leaf longevity.

The effects of a number of factors, notably leaf mining insects, on the longevity of beech and holm oak leaves have been studied. The regular monitoring of individually labelled leaves was complemented by analysis of leaf fall data. Both methods confirm that these mining insects have only a slight impact on their host trees. The presence of first generation Phyllonorycter maestingella mines on beech leaves and winter generation P. messaniella mines on holm oak leaves accelerates leaf loss. Beech leaves mined by second generation P. maestingella and Rhynchaenus fagi did not show this accelerated loss. Their patterns of leaf fall can be explained by within-tree variation in both mine distribution and the timing of leaf fall. It is argued that this premature leaf fall is a damage response, and is not an attempt by the tree to regulate miner numbers.

Life cycles and drift of Trichoptera from a woodland stream in Minnesota

Life cycles of Trichoptera from a stream riffle were determined from analyses of monthly size–frequency distributions of larvae, pupal densities, and observations of adult emergence. Two types of univoltine life cycles were observed (H. B. N. Hynes' classification): slow seasonal for Brachycentrus americanus, Brachycentrus occidentalism and Micrasema kluane, and fast seasonal for Lepidostoma bryanti. The life cycle for Glossosoma intermedium was primarily bivoltine with summer and winter generations; however, some larvae of the summer generation were suspected to overwinter as pupae or terminal instar larvae and emerge in the spring. Larval B. americanus and L. bryanti showed peak drift prior to pupation and emergence which thus appeared seasonally associated with life cycle. Stream drift of M. kluane and G. intermedium was low and exhibited no clear association with life cycle or season. Drift of B. americanus, M. kluane, L. bryanti, and G. intermedium was not correlated to standing stocks (p < 0.05).

Peach Twig Borer, Anarsia lineatella Zeller (Lepidoptera: Gelechiidae), Development in Washington and California

Lower and upper developmental thresholds for Anarsia lineatella Zeller based on egg duration and adult flight were 10 and 3l.1°C, respectively. Generation time ranged from 514 to 612 day-degrees. Adult flight of the winter generation was first observed 118 day-degrees after first pupation of overwinter larvae. Shoot flagging was observed 260 day-degrees after the first moth. The average day-degree duration for each insect stage is given. Parameters are suggested for using the PETE generalized-phenology model.

Growth and moulting of Neomysis integer (Crustacea: Mysidacea)

The growth and moulting of Neomysis integer (Leach) was investigated in the field and the laboratory. In the Ythan estuary, Aberdeenshire, Scotland, monthly samples taken from November 1976 to October 1978 revealed that the summer generation juveniles and mature individuals grew at a rate of 4 to 5 mm and 1 to 2 mm monthly, respectively. The winter generation had a growth rate of 3 to 4 mm monthly for juveniles and about 1 mm for mature individuals; during the winter there was a period of 3 mo when growth was almost completely stopped. Mysids reared in the laboratory on Artemia sp. nauplii had an average daily growth rate of 0.06 mm at 9°C and 0.09 mm at 16°C. The growth factors of N. integer ranged from 3 to 17% for mature and immature individuals, respectively. Intermoult periods ranged from 3 to 7 d in immature mysids to 12 to 18 d in mature mysids. Average laboratory growth curves calculated from information on growth factors and intermoult periods indicate that at 9°C (winter generation) it takes N. integer 277 d to grow to be a 15 mm mature individual, whereas at 16°C (summer generation) it takes 188 d. N. integer moults 24 times as it grows from a juvenile to a mature individual.

Life history and microdistribution of Neureclipsis bimaculata (Trichoptera: Polycentropodidae) in a lake outflow stream of Alberta, Canada

A population of Neureclipsis bimaculata was studied from November 1980 to September 1982. The life cycle was bivoltine during both years. Development was direct and the population overwintered as larvae. The summer generation took only 6 to 7 weeks to complete, while the winter generation took the remainder of the year. Adult emergence took place from late May to early September, with two distinct peaks corresponding to the two generations. In both years summer generation larvae and adults were much more numerous than the winter generation. Production of this population (both generations) was estimated at 3.43 g∙m−2∙year−1 (ash free dry mass). The type and abundance of aquatic macrophytes influenced larval microdistribution by acting as a substratum for the large capture nets of larvae. Potamogeton richardsonii and Equisetum were important substrata in summer. In winter, Chara was an important substratum, since it was the only major structural component on the mud-sand bottom during that season. Maintenance of capture nets was seasonal (May to September or early October) and appeared to be related to temperature. Cumulative degree-days were not sufficient to account for apparent differences in voltinism between populations; these differences may be a function of food supply, which in part is related to the productivity of the water body.

Life histories of some filter-feeding Trichoptera in Virginia

Life histories were determined for seven species of filter-feeding Trichoptera at two sites on the impounded North Anna River and at two sites on the free-flowing South Anna River in the Piedmont of Virginia, U.S.A. Hydropsyche incommoda, H. sparna, and H. venularis were trivoltine at at least three of the four sites, with fast-growing spring and summer generations that matured in June and July, and August and September, respectively, and a slow-growing winter generation that matured in March, April, and May. Cheumatopsyche parentum, Macronema zebratum, Chimarra moselyi, and C. obscura were bivoltine at all sites. The summer generations of these species grew quickly, maturing in June and July, and the winter generation grew slowly, maturing in April and May. Instars I–V, pupae, and adults of most species were present continually from April through October. All species overwintered in instars III–V, and in most species instar II was present during the winter also. Comparisons of Hydropsyche life histories in the Anna Rivers with those reported from other eastern North America rivers reveal that differences in voltinism are probably due to a complex interaction of food quality and temperature regime.

Variation in life-history patterns of the grass shrimp Palaemonetes pugio in two South Carolina estuarine systems

A population of Palaemonetes pugio Holthuis 1949, inhabiting a fairly constant high salinity estuarine environment (North Inlet), exhibited more rapid growth, earlier first reproduction, a smaller clutch size, more fluctuating sex ratio, and shorter life span. A population in a less saline environment (Minim Creek) showed relatively slower growth, delayed first reproduction, larger clutch size, female-dominated sex ratio, and longer life span. Growth in both areas was rapid in summer and slower in winter, with the females growing much larger than the males. Summer generation females first reproduced at the age of 3.5 months in North Inlet and at 4.8 months in Minim Creek. Minim Creek females larger than 30-mm TL carried more eggs than North Inlet females of similar sizes. Life span in North Inlet was calculated to be 6–7 months for the summer generation and 9–10 months for the winter generation; in Minim Creek, the corresponding longevity estimates were 9–10 months and 12–13 months, respectively. Variations in life history patterns are hypothesized to be the results of numerous environmental factors acting differentially on the various life-stages of the organism. The results suggest that the reproductive flexibility of P. pugio enhances its ability to persist in a variety of environments.

Determination of the number of instars and size variation in the larvae and pupae of Simulium chutteri Lewis 1965 (Diptera: Simuliidae) and some possible bionomical implications

Morphometric studies show that there are seven larval instars in Simulium chutteri. A guide for separating instars of S. chutteri is included. Seasonal and sexual size variation and seasonal variation in biomass in larvae and pupae of S. chutteri are statistically analysed and discussed. Water temperature is a major factor in determining larval and pupal size variation and duration of the pupal stage. Growth in S. chutteri follows a geometric pattern and is in agreement with previous works on other species. An overlap of larger and smaller larvae at the same developmental stage resulted from the coexistence of early winter and late summer generations, respectively. Larger larvae and pupae can result in autogenous and more fecund adult females. This is important in the population dynamics of this pest species and can lead to sudden unexpected population explosions. It is suggested that population explosions could be controlled by sharply reducing the population of large individuals of S. chutteri in the spring.

Growth patterns and food habits of Baetis rhodani, Capnia pygmaea and Diura nanseni in a West Norwegian river

As a part of weir‐pond‐ecosystem project, the growth patterns and food habits of Baetis rhodani (Ephemeroptera), Capnia pygmaea (Plecoptera), and Diura nanseni (Plecoptera) were investigated. B. rhodani was bivoltine. The winter generation consisted of three cohorts. C. pygmaea and D. nanseni accomplished their nymphal growth in one year. The predominate food consumed by B. rhodani and C. pygmaea was detritus. Variations in the diet of these detritivores are discussed in relation to microdistribution and possible competition. The most common prey items of the carnivorous D. nanseni were chironomids and nymphs of B. rhodani and C. pygmaea. Prey shortage is suggested to be the reason for small D. nanseni eating detritus.

The life histories of the amphipods Lembos websteri Bate and Corophium bonnellii Milne Edwards in kelp holdfasts

The life cycles of Lembos websleri Bate and Corophium bonnellii Milne Edwards are based on two generations per year. Eight cohorts have been identified in Lembos and nine for Corophium, each of which has a different longevity. In Lembos the summer generation proper lives ≈ 5–7 months whilst cohorts of the overwintering population may live up to 11.5 months. Males do not live as long as females, their longevity being ≈ 11% less in summer and 5% less in winter. C. bonnellii is parthenogenetic. Its summer generation lives ≈ 5 months and its winter generation 8–10 months. Corophium thus has a shorter life span than Lembos. It also grows faster. Growth is severely inhibited overwinter (but less so in Corophium) and picks up in spring. Year to year variations in timing of reproductive events may be related to temperature differences, sea state, and food supply. Population data for 1974 and 1975 were, however, generally very similar. Ovigerous females are present all the year in Lembos websteri but were never found in January in Corophium bonnellii. Egg-laying behaviour is described. Brood size is linearly related to maternal length in both species. A size-independent index of fecundity shows clear seasonal variation, with peak fecundity in summer. Minimum size of egg-bearing females is also a function of temperature in both species. A semi-lunar rhythmicity of brood production at summer temperatures is reported. Brood mortalities of ≈ 25–30% were found in both species which seemed unrelated to maternal size but which may (in Lembos) be seasonally variable (lower in winter). Egg size is similar in both species and egg volume more than doubles during development from Stage I to Stage IV. Corophium bonnellii eggs are bigger and individual female reproductive effort is higher than in other Corophium species. Corophium sometimes carried the ciliate Conidophrys on the basal segments of its antennae. Occasional endoparasites, namely cercariae and encysted metacercariae, were noted. Mortality due to fish predation was established to occur, the clingfish Apletodon microcephalus (Brook) and the sea snail Liparis liparis (L.) being important amphipod consumers.

Quantitative studies on the eggs of Simulium (Simulium) ornatum Meigen and Simulium (Wilhelmia) equinum L. in a chalk stream in southern England

Abstract. The egg masses of Simulium ornatum, S.equinum and S.vernum are described and information is given on numbers of eggs per egg mass and the size and number of batches laid by individual females. The oviposition sites were studied in relation to water velocity, wind speed and direction. The incubation periods at different river temperatures and the effects of desiccation on percentage hatch and incubation times were investigated. The numbers of eggs laid were assessed for the winter generations of S. ornatum and S.equinum. The relevance of these to the overall production estimates is discussed