A multi-generation Calanus finmarchicus culturing system for use in long-term oil exposure experiments

Crustacean zooplankton form the keystone link between primary producers and fish stocks along the Norwegian shelf and in the southern part of the Barents Sea. We have established a multi-generation cultivation system for zooplankton in order to perform future experiments on the biological effects of drilling discharges from the offshore petroleum industry. A population of the cold-water species, Calanus finmarchicus, was collected in March 2004 and maintained in a static system of 100 l polypropylene containers through all stages (Eggs-CVI). The population exhibited an average developmental time of 105 days which corresponds to realistic sub-Arctic to Arctic conditions (water temperatures = 5 °C (spring) and 8 °C (late summer)). A series of experiments was performed to examine copepod egg production as a function of different food sources and feeding concentrations. Only minor differences in egg production were observed for C. finmarchicus females fed with varying concentrations of the two diatom species Chaetoceros socialis and Thalassiosira weissflogii. In a separate experiment, the response to food availability was examined over time by tracking egg production and fecal pellet production (used as an indicator of food ingestion). Both hatching success and food ingestion were positively correlated with the food concentrations offered to adult females. Through this work we have demonstrated that C. finmarchicus populations can be maintained in the laboratory through multiple generations. In addition, methods to control egg production through changes in food availability have been established making it feasible to control the start date of exposure experiments or the timing of the collection of eggs to initiate a new generation.     

Postinfection Development of Rotylenchulus reniformis on Resistant Gossypium barbadense Accessions

The reniform nematode (Rotylenchulus reniformis) causes significant cotton (Gossypium hirsutum) losses in the southeastern United States. The research objective was to describe the effects of two resistant G. barbadense lines (cultivar TX 110 and accession GB 713) on development and fecundity of reniform nematode. Nematode development and fecundity were evaluated on the resistant lines and susceptible G. hirsutum cultivar Deltapine 16 in three repeated growth chamber experiments. Nematode development on roots early and late in the infection cycle was measured at set intervals from 1 to 25 d after inoculation (DAI) and genotypes were compared based on the number of nematodes in four developmental stages (vermiform, swelling, reniform, and gravid). At 15, 20, and 25 DAI, egg production by individual females parasitizing each genotype was measured. Unique reniform nematode developmental patterns were noted on each of the cotton genotypes. During the early stages of infection, infection and development occurred 1 d faster on susceptible cotton than on the resistant genotypes. Later, progression to the reniform and gravid stages of development occurred first on the susceptible genotype, followed by G. barbadense cultivar TX 110, and finally G. barbadense accession GB 713. Egg production by individual nematodes infecting the three genotypes was similar. This study corroborates delayed development previously reported on G. barbadense cultivar TX 110 and is the first report of delayed infection and development associated with G. barbadense accession GB 713. The different developmental patterns in the resistant genotypes suggest that unique or additional loci may confer resistance in these two lines.     

The effect of food limitation on gonad development and egg production of the planktonic copepod Calanus finmarchicus

Calanus finmarchicus, one of the dominant copepods species of the North Atlantic, often encounters low food concentration or quality during the reproductive period; however, our knowledge on the effect of these conditions on reproduction processes is scarce. The present study combines experiments with histological observations to describe the response of C. finmarchicus to limited food focussing on (1) oocyte maturation processes, (2) gonad morphology, (3) egg production rates as a function of spawning frequency and clutch size, and (4) the fuelling of egg production by measuring carbon and nitrogen content of the females. In the laboratory, C. finmarchicus females were exposed to 0, 10, 50, 150 or >300 μg C l⁻¹ for several days. To account for food quality and season, reproductive activity was compared in April and July 1999 between females feeding on diatoms or dinoflagellates. The effect of feeding history was studied in February with females fed and starving prior to the experiment. Feeding conditions had severe effects on oocyte maturation process. Hence, egg production varied significantly with food concentration and quality, season and feeding history due to variation in both clutch size and spawning frequency. Clutch size differed by a factor of 2-4 between food limited and well fed females, and is thus an important parameter for modelling egg production. Changes in clutch size were related to changes of the number of maturing oocytes in the females gonads indicating that the latter can be used to precise the prediction of egg production from preserved samples. The proportion of females carrying at least some mature oocytes was relatively high at low food availability. Apparently, these females used internal body reserves as the carbon and nitrogen content decreased significantly under these conditions. These results indicate that C. finmarchicus embarks on the strategy to enable reproduction in all or many females of a population at low rates when feeding conditions are unfavourable.     

Effects of chlorophyll concentration and temperature variation on the reproduction and survival of Temora longicornis (Copepoda, Calanoida) in the Eastern English Channel

The influence of temperature and chlorophyll concentration on egg production, hatching success, female survival and body size of the copepod Temora longicornis was investigated in situ in the coastal waters of the Eastern English Channel. Twenty samples were collected between February and July 2003 three to four times per month. The maximum daily level of egg production of 75.5 eggs female⁻¹ was observed in March, with minima of 10 eggs female⁻¹ in February and July. Between February and March egg production increased with chlorophyll concentration. At the end of March a decrease in egg production corresponded to a strong increase in chlorophyll concentration that indicated a Phaeocystis-dominated bloom. After this period egg production closely followed the temporal variation in chlorophyll concentration with a maximum of 55.3 eggs female⁻¹ in April during a second peak of chlorophyll concentration. Hatching success varied between 60% and 80% and was not influenced by chlorophyll concentration, in situ temperature or any other biological parameter considered in this study. Increases in temperature from February to July paralleled a decrease in body length and an increase in the percentage of spawning females. Mean female survival followed the variation of both temperature and chlorophyll concentration only between April and July. Temperature and chlorophyll concentration affected the reproductive parameters of T. longicornis differently. Female survival and body size were negatively correlated with temperature, while the highest chlorophyll concentrations were not always favourable for egg production. Therefore the quality of food should not be associated with chlorophyll quantity. Furthermore, the maximum values of egg production in this study are the highest recorded for T. longicornis. This study, conducted for the first time in the Eastern English Channel, showed high levels of productivity of T. longicornis despite a decrease of egg production during a Phaeocystis sp. dominated bloom in April.     

Reproductive activity and physiological status of the calanoid copepods Calanus helgolandicus and Calanoides carinatus under food-limiting conditions

The reproductive activity and the physiological state of the calanoid copepods Calanus helgolandicus and Calanoides carinatus were investigated off the coast of NW Spain during autumn to evaluate the effect of short food resources on both populations. Phytoplankton biomass was low, and neither phytoplankton size distribution nor composition was suitable to support high reproductive rates. Accordingly, egg production rates (EPR) were much lower than maximum rates for both species, pointing to food limitation. The reproductive index (RI), which represents the proportion of females with mature gonads, was < 50% at each of the three zones into which the sampling area was divided (coast, shelf and ocean). Potential recruitment rates were very low except at some nearshore stations, where the highest concentrations of chlorophyll-a (Chl-a), diatoms, dinoflagellates and large cells were found. EPR of C. helgolandicus and C. carinatus were correlated with phytoplankton biomass and unaffected by temperature. Phytoplankton carbon ingestion explained ca. 50% of the variability in EPR for both species. At most of the stations, herbivory was insufficient to cover the carbon requirements for reproduction and respiration, so females probably fed on heterotrophic prey to meet their demands. However, given the low fecundity observed, this omnivorous diet did not seem to be optimum for reproduction, and a severe food limitation is thus suggested. Furthermore, the high C/N values measured point to a notable lipid storage, but given the low EPR found, lipid reserves were probably invested into female maintenance rather than into gonad maturation. C. helgolandicus and C. carinatus populations did not mirror phytoplankton biomass distribution, but they correlated well when considering only copepodites V (CV). The CV could be preparing for the overwintering, storing lipid reserves to ensure a successful diapause, and they could also be advected by the poleward current detected during the study. Females showed a diel feeding rhythm, with highest ingestion rates during night. From our results, it follows that C. helgolandicus and C. carinatus females did not perform diel vertical migrations. We suggest that this behaviour is likely due to the food-limiting conditions, which make it more advantageous to remain at the surface during daytime.     

Nucleic acid indices of egg production in the tropical copepod Acartia sinjiensis

Two experiments were conducted to evaluate the effects of food and temperature on the nucleic acid content and egg production (and their relationship) of the tropical copepod Acartia sinjiensis. Experiment 1 evaluated the effect of food quality (as different algae species) on the relationship between nucleic acid content and egg production. In Experiment 2, the main and interaction effects of food type, food concentration and temperature on the total, Carbon and Nitrogen specific egg production and nucleic acid indices were evaluated in a factorial experimental design. Food quality, concentration and temperature significantly affected the nucleic acid content, egg production rate and the nucleic acid-egg production relationship of A. sinjiensis. RNA indices were correlated with egg production in females fed Pavlova salina, Tetraselmis chuii and Chaetoceros muelleri, but not in females fed Isochrysis aff. galbana. The slopes of the linear regressions of RNA indices as predictors of egg production were similar in females fed different algae species, suggesting that the slope of these relationships might be independent of food quality. The DNA content of females was significantly affected by food and temperature, suggesting that it is not a good index of cell number in this species. Nevertheless, the RNA:DNA ratio was as good a predictor of egg production as total RNA content. Egg production showed a weakly positive correlation with temperature. On the other hand, total, C- and N-specific nucleic acid indices had a strong negative correlation with temperature. In addition, temperature had a non linear effect on the slopes of the regression lines of RNA content and RNA:DNA ratio as predictors of egg production—slopes were similar at 25 °C and 30 °C, but significantly lower at 20 °C. Furthermore, the predictability of egg production was improved when the interaction term of nucleic acid indices with temperature was used instead of the nucleic acid indices alone in linear regression models. Our results suggest food quality has a limited influence on the nucleic acid-egg production relationship, and that temperature should be accounted for in models using nucleic acid indices as predictors of egg production in A. sinjiensis.     

Oogenesis and gonad maturation in the copepodCalanus finmarchicus and the prediction of egg production from preserved samples

 Oogenesis and gonad development of Calanus finmarchicus during the winter spring transition in a fjord in Northern Norway were studied. A combination of observations on whole animals (macroscopic), taking advantage of their transparency, and histological sections was used to establish a system of gonad maturation stages, to describe the spawning cycle and to estimate egg production rates from preserved samples. During their development, oocytes change their shape and size, the morphology of the nucleus, and the appearance of the ooplasm. Four oocyte development stages were identified and related to a macroscopic system of four gonad developmental stages (GS) that can be applied to whole stained animals. During gonad development, the macroscopic morphological modifications of the gonads are mainly manifested in an increase in number and size of the oocytes and their distribution in diverticula and oviducts. The maturation processes during the spawning cycle (the period between egg depositions) were described from histological sections of females preserved at regular intervals after egg deposition. The macroscopic GS did not vary during the spawning cycle. This GS was a highly significant indicator for females, which spawned within 24 h after collection at 5°C. Another histological indicator for the last third of the spawning cycle is the appearance of distinct chromosomes, which, however, are only seen in histological sections. For the prediction of egg production rate of a Calanus population, in addition to the number of females spawning, knowledge of clutch size and the interval of clutch deposition is required. Clutch size was determined by counting the number of the oocyte stages to be released during the next spawning event in serial sections of the gonads. There was no significant difference in clutches laid by the females during 5 days before preservation. From the observations it seems that GS 4 predicts females that are ready to spawn within the minimum spawning interval characterisitic for a given temperature. If this holds true, it should be possible to predict in situ egg production rates solely from preserved samples. Received: 18 August 1995/Accepted: 6 January 1996     

Temperature impact on reproduction and development of congener copepod populations

The goal of this study was to relate the temperature response of all developmental stages and reproductive biology of two congener copepod pairs inhabiting different biogeographic regions to their geographic distribution patterns. Survival of adult females and egg production, embryonic development and hatching success of the genera Centropages and Temora from two stations, in the North Sea and the Mediterranean, were studied in laboratory experiments in a temperature range from 2 to 35 °C. Postembryonic development was determined from cohorts raised at temperatures between 10 and 20 °C with surplus food. Tolerance limits and optima of female survival, reproduction and development distinguished the northern species Centropages hamatus and Temora longicornis from the southern T. stylifera, while C. typicus, which is found in both regions, was intermediate. Thus, thermal preferences could in part explain distribution patterns of these species. While C. hamatus and the two Temora species showed distinct temperature ranges, C. typicus was able to tolerate different temperature conditions, resulting in its wide distribution range from the subarctic to the tropics. However, the thermal range of a species did not necessarily correlate with the optimal temperatures in the experiments. Optima of egg production and stage development were surprisingly low in T. stylifera, which has a mere southern distribution.     

Copepod feeding behaviour and egg production during a dinoflagellate bloom in the North Sea

Feeding strategies of copepods were studied during a dinoflagellate-dominated bloom in the North Sea in August 2001. The aim of this study was to evaluate the importance of mesozooplankton grazing as a biological loss factor of harmful algal blooms under natural conditions. Therefore, ingestion, egestion and egg production experiments were performed with the most abundant copepod species Calanus helgolandicus, Temora longicornis and Acartia sp. feeding on the natural phytoplankton community. Dinophysis norvegica and Ceratium furca were the most abundant dinoflagellate species at the time of the experiments. Grazing experiments as well as examination of fecal pellet content revealed C. helgolandicus fed efficiently on D. norvegica. Ingestion rates up to 47 cells female⁻¹ h⁻¹ were measured and a large proportion of the C. helgolandicus fecal pellets contained intact D. norvegica cells. Dinophysis cells were rarely seen in fecal pellets produced by T. longicornis, and never observed in pellets produced by Acartia sp. The ingestion rate of C. furca, which was the dominating Ceratium species, mimicked that of D. norvegica. C. helgolandicus grazed significantly on C. furca (16 cells female⁻¹ h⁻¹), while the ingestion rate of T. longicornis was low and Acartia sp. was not able to graze on C. furca. Egg production experiments revealed that 92% of the C. helgolandicus females produced eggs. The specific egg production rate and the proportion of females producing eggs among T. longicornis were low. This field experiment clearly shows that some copepod species feed efficiently on D. norvegica and C. furca under natural conditions, which may affect the bloom development of these dinoflagellates.     

Mode of Parasitism of Meloidogyne and Other Nemaiode Eggs by Dactylella oviparasitica

Hyphae of Dactylella oviparasitica proliferated rapidly through MeIoidogyne egg masses, and appressoria formed when they contacted eggs. The fungus probably penetrated egg shells mechanically, although chitinase production detected in culture suggested that enzymatic penetration was also possible. In soil, D. oviparasitica invaded egg masses soon after they were deposited on the root surface and eventually parasitized most of the first eggs laid. Occasionally the fungus grew into Meloidogyne females, halting egg production prematurely. The fungus parasitized eggs in the gelatinous matrix or eggs freed from the matrix and placed on agar or in soil. Specificity in nematode egg parasitism was not displayed, for D. oviparasitica parasitized eggs of four Meloidogyne spp., Acrobeloides sp., Heterodera schachtii, and Tylenchulus semipenetrans. In tests in a growth chamber, parasitism by D. oviparasitica suppressed galling on M. incognita-infected tomato plants.     

Development and biological characteristics of <Emphasis Type="Italic">Haemaphysalis longicornis</Emphasis> (Acari: Ixodidae) under field conditions

The development and biological characteristics of Haemaphysalis longicornis were investigated under field conditions in Xiaowutai National Natural Reserve Area, North China. Unfed larvae, nymphs and adults were fed on rabbits and exposed to daylight. Three free-living stages were allowed to develop in field plot selected in a tick natural habitat. The host seeking behavior and seasonal occurrence were observed. Haemaphysalis longicornis were active from mid March to mid October. The premoult period of nymphs and preoviposition of females were regulating phases of their life cycle. The developmental durations of eggs, larvae and adults were constant under field conditions regardless when the development started. The oviposition periods in May and June were statistically shorter than those in July and August. The daily oviposition patterns of females engorged in May and June demonstrated unobvious peak, which differed from those engorged in July and August. The daily oviposition peak of the latter occurred on the 4th day of oviposition. Moreover, a positive correlation was found between the mass of the laid egg and the body weight of engorged females (r = 0.62, P < 0.001). The female reproductive efficiency indices were 2.9, 6.1, 10.5 and 9.0 in May, June, July and August, respectively. The mean weight (3.33 mg) of engorged nymphs molting to females was significantly higher than that (2.35 mg) of those molting to males (P < 0.001), but the body weights of both sexes were overlapping.     

Effects of ultraviolet-B stressed diatom food on the reproductive output in Mediterranean Calanus helgolandicus (Crustacea; Copepoda)

Recent predictions anticipate a solar ultraviolet-B increase of 5-10% over temperate latitudes within the next 15 years. As Mediterranean waters are clear, enabling deep UVB penetration, we used controlled experiments to test the effects of equivalent levels of UVB on trophic plankton interactions. We grew the diatom Skeletonema costatum in the laboratory under daily 4 h UVB exposure in doses of 10% higher than today in contrast to control cultures (no UVB). UVB-exposed algae showed modification in cell structure, volume increase and delay in cell division, eventually leading to lysis and cell death after five days of daily 4 h exposure. Both control and UVB-stressed S. costatum cultures were used as food for wild Calanus helgolandicus females collected in the NW Mediterranean. Those fed on control diatoms produced three times more eggs, healthier offspring with fewer lethal naupliar deformities than females fed on UVB-exposed diatoms. Our results provide the first experimental evidence of indirect UVB effects on reproductive output through trophic response in marine plankton. The sensitivity of the S. costatum strain is discussed as well as the reduced reproductive output of the female copepods. We suggest that the low egg numbers and high naupliar deformity ratios are possibly a consequence of UVB-induced deficiency of essential components in the UVB-stressed maternal diet.     

Egg production of the copepod Acartia bifilosa in two contrasting European estuaries in relation to seston composition

The egg production of the copepod Acartia bifilosa was measured and related to environmental variables and food availability in two estuaries located in the same biogeographic region (Bay of Biscay) but showing very strong differences in abiotic and biotic features: the Gironde estuary (France) and the estuary of Mundaka (Spain). The study was conducted during the spring-summer-autumn period of 1994. Food availability was evaluated by analysing the chlorophyll a (Chl a), the particulate organic carbon (POC) and the easily extractable macromolecular compounds such as proteins, carbohydrates and lipids of the seston. The egg production of copepods was estimated from field incubations with natural water, and phytoplankton feeding of adult females was estimated by means of the gut fluorescence method. The nutritional environment of the Gironde was characterised by high amounts of suspended particulate matter (SPM) with low food value, emphasising the mainly detrital origin of the organic matter (OM). In Mundaka, the higher contribution of phytoplankton to the seston led to marked increases in particulate food value accounting for up to 35% of organic matter. The weight-specific egg production was found to be sharply higher in Mundaka (ranging from 0.2 to 0.63×10⁻³ day⁻¹) than in the Gironde (ranging from 0 to 0.13×10⁻³ day⁻¹), but the seasonal trend of variations was similar, the highest weight-specific egg production rates occurring in early summer and the lowest in autumn in both estuaries. Egg production was not correlated linearly with temperature since maximal egg production occurred at intermediate temperatures. In Mundaka, the egg production showed a significant positive correlation with the chlorophyll and the Chl/SPM and the POC/SPM ratios. This coupled with higher values of algal food availability (Chl a/SPM: 10 to 1870 μg g⁻¹) and gut fluorescence (between 0.12 and 0.38 ng Chl a Eq ind⁻¹) indicate that a herbivorous diet could cover the energy requirements of A. bifilosa and support egg production. In the Gironde, the algal food availability and the gut fluorescence were lower (Chl a/SPM: 10 to 80 μg g⁻¹; GF: 0.09 and 0.25 ng Chl a Eq ind⁻¹), and the egg production showed significant positive correlation with the particulate food value, suggesting that other sources of carbon rather than phytoplankton were responsible for the observed changes in egg production. Results indicate that the particular seston properties of each system may be responsible for the noticeable differences in A. bifilosa fertility among estuaries.     

Temporal variability in egg production rates of Acartia tonsa Dana in Long Island Sound

The relationship between week-by-week variations in the in situ egg production rates of Acartia tonsa Dana and changes in chlorophyll concentration in several size fractions was investigated by incubating adult females in natural sea water for 24-h periods. Our results indicate that the egg production of A. tonsa in Long Island Sound was better related to the 10 μm chlorophyll size fraction than to the total chlorophyll concentration. The < 10 μm size fraction comprised the greatest percentage of the chlorophyll during July and August when the water column was stratified. Egg production rates were lowest (8.7 eggs · female⁻¹ · day⁻¹) in early August when less than 0.5 μg chlorophyll 1 ⁻¹ was observed in the 10 μm chlorophyll a size fraction. Following destratification in late August, the “fall” diatom bloom occurred and egg production rates increased to the maximum observed rate of 56.6 eggs · female⁻¹ · day⁻¹. At this time, the concentration of the 10μm chlorophyll size fraction was 5.5 μg 1⁻¹. Maximum egg production rates were observed at chlorophyll concentrations as low as 0.8 μg 1⁻¹ in the 10 μm size fraction.     

Survival and diapause egg production of the copepod Centropages hamatus raised on dinoflagellate diets

Copepods are often said to require a mixed diet to maximize their survival and reproduction potential. Copepods may be forced to feed nonselectively in food limited environments, but this does not mean they require a diverse diet. In this study, we show that the right single food item, at the right stage, can be as good or better than a mixed diet for development, survival, diapause egg production and viability. Centropages hamatus was reared on unialgal or mixed diets of five dinoflagellates: Amphidinium carterae, Prorocentrum micans, Scrippsiella trochoidea, Lingulodinium polyedra, and Gymnodinium sanguineum, ranging in size from 11×16 μm to 44×57 μm. Four experiments of 12-30 days were conducted, each testing five diets against a mixed Control diet of the four larger dinoflagellates. Algal volumes were adjusted so diets would have the same initial carbon content or cell volume at a level known to be in excess of the amount required for growth. Eggs were collected on the final 2 days of the experiments, the survivors were counted and female prosome length was measured. Diapause egg viability was measured after the eggs completed a refractory period. Nauplii had high survival on unialgal P. micans and S. trochoidea diets, but the adult females did not produce eggs. Naupliar survival was low on a unialgal diet of G. sanguineum, but the adult females had the highest rate of egg production. An optimal diet fosters growth and survival at all stages and maximizes viable egg production, to ensure high recruitment to the next generation. This can be achieved with single food items appropriate for the developmental stage. Copepods fed just two dinoflagellates, P. micans to foster juvenile growth and G. sanguineum to support final maturation and fecundity, had higher total egg production than copepods reared on the mixed diet of four dinoflagellates.     

Measuring production and viability of eggs in Calanus helgolandicus

The effect of several biotic and abiotic factors on the fecundityand hatching success of Calanus helgolandicus was tested duringshort- and long-term incubations. The results show that thevariations of the reproductive responses of C.helgolandicusare time dependent and rely on the type of factor tested. Whenstandardized over a 24 h incubation period, estimates ofin situproduction and egg viability can be obtained with good accuracy.     

Parentage analyses of freshwater goby Rhinogobius sp. OR using microsatellite DNA markers and egg developmental stages of eggs in the nest

Parentage analyses of the paternally caring goby Rhinogobius sp. OR were performed using microsatellite DNA markers and examination of developmental stages of eggs collected from five nests with parental males in the wild. Four of five nests had egg masses with eggs at the same developmental stages from single females. In one nest, the egg mass with eggs at three different developmental stages originated from four females, and eggs of whole developmental stages were observed within the egg mass of each female. This observation suggests that in this goby embryonic stage is an inaccurate indicator of the number of mates.     

Morphological Features and Hatching Patterns of Eggs in Acartia Steueri (Crustacea, Copepoda) from Sagami Bay, Japan

Morphology, production rate and hatching success of the eggs spawned by Acartia steueri from Sagami Bay, Japan were examined from November 2000 to December 2001. A. steueri produced two morphological types of egg. One with a smooth surface (smooth egg) and the other with branched spines on the envelope (spiny egg). Abundance of adult A. steueri increased from April to June 2001, and then decreased from July 2001. Adult A. steueri were low in abundance between August and October 2001, then increased in November 2001. Smooth eggs were produced through out the study period, while spiny eggs were produced during restricted periods from March to July 2001. Six of thirteen females produced both smooth and spiny eggs within 24 h. All the smooth eggs hatched within 48 h, like the so-called subitaneous eggs. Spiny eggs that did not hatch within the time determined by the Bělehrádek's temperature function of egg development time plus 24 h were categorized as diapausing eggs. In the present study, A. steueri seems to survive by utilizing egg dormancy during the period of environmental adversity, and produced two physiologically different types of eggs. This may be why A. steueri dominants in temperate coastal waters where environmental conditions vary drastically.     

The reproductive output of sea lice Caligus rogercresseyi under controlled conditions

Gravid females of Caligus rogercresseyi were collected from Atlantic salmon (Salmo salar) from a farm located at Chiloe Island (42°40′S73°15′W), Chile, to obtain information about the reproductive output of this parasite in vitro. The egg strings removed from the females were incubated under controlled conditions to obtain virgin adult females. One female which had mated only once produced eleven generations of eggs strings in a period of 74 days. The first egg strings of the females obtained in vitro were produced at 389 degree days (°D) after egg incubation, while the next generations of eggs strings were produced with a periodicity between 4 and 6 days dependent on the water temperature. The average length of the egg string was 3.1 mm and the mean number of eggs per string was 31. The values recorded in captivity for the egg string length and the number of eggs per string, were lower than the values recorded in gravid females from the field. One female survived for 79 days and males, maintained separately from the females, survived for 60 days.     

Ontogeny and reproductive biology of Diadegma semiclausum (Hym.: Ichneumonidae), a larval endoparasitoid of Diamondback Moth,Plutella xylostella (Lep.: Plutellidae)

In this article, the ontogeny and reproductive biology of Diadegma semiclausum (Hym.: Ichneumonidae), an important parasitoid of Plutella xylostella (Lep.: Plutellidae) are described in detail. We did dissect parasitized P. xylostella larvae in phosphate-buffered saline and determine the external morphology of its parasitoid at all developmental stages. The developmental duration of its immature stages, adult longevity, total oviposition period and fecundity of the parasitoid are determined at 24 ± 1 °C, 65  ±  5% R.H., and a photoperiod of 16:8 h L:D. The mean duration of egg and larval stages is 9.56 days and the prepupa and pupa stages last for 8.27 days. In average, female longevity is 1.31 times longer than that of males, and females lay 300 eggs in total. The peak of D. semiclausum oviposition is on the eighth day after mating. The egg loading pattern of D. semiclausum was investigated to determine the parasitoid ‘ovigeny index’ throughout the female's parasitoid lifetime. Initial egg load in immature females (<2 h age) is 1.45 per female and the mean lifetime potential fecundity (total immature and mature oocytes), at four interval ages, is 34. With an ovigeny index value of 0.038, D. semiclausum is considered moderately to strongly synovigenic. In the absence of the host, after 3 days, the number of eggs is decreased in D. semiclausum. Our results demonstrated that there is a negative relation between the ovigeny index and egg resorption in this parasitoid.