Instar IV Research Articles

Effects of different diets on thermal tolerance in the silkworm, Bombyx mori

AbstractThe survival of species is negatively impacted by the increased frequency and intensity of high‐temperature episodes caused by increased global warming. Thermal tolerance can influence population size and the geographic distribution of species, which translates into species‐wide responses to climate and affects interactions between communities of species. The silkworm, Bombyx mori (L.) (Lepidoptera: Bombycidae), is an ectotherm and an internationally recognized model insect for studying sensitivity to the environment. In the present study, we investigated the effects of different diets on the thermal tolerance of silkworm. As such, it was identified that silkworms reared on an artificial diet in instars I–III and mulberry leaves in instar IV (referred as the AM group) exhibited faster weight gain and higher antioxidant enzyme activity at 35 °C, whereas silkworms reared only on mulberry leaves (referred as the ML group) exhibited upregulated transcript levels of key genes regulating antioxidant enzyme signaling pathways including Akt, CncC, and keap1, significantly increased reactive oxygen species (ROS) levels, and severely impaired midgut activity at 35 °C. Thus, the AM group presented stronger thermal tolerance. These findings suggest that diet can affect the thermal tolerance of silkworm. This research improved our understanding of the molecular, biochemical, and physiological changes caused by thermal stress and laid the groundwork for future research regarding the mechanism underlying thermal tolerance. Furthermore, this study provides an important reference for the conservation of biodiversity in the context of global warming.

Chironomus calligraphus Goeldi, 1905 (Diptera: Chironomidae) Larvae: Feeding Habits, Growth, and Maturation.

Chironomus calligraphus Goeldi, 1905 has a flexible life cycle with several generations per year, which can be modified by the quality and type of food. To categorize the functional feeding group of the species, food preference was evaluated in larval instars III and IV, through laboratory experiments and gut content analysis. To evaluate the influence of the type of food on the duration of the life cycle growth and maturation, experiments were carried out. Instar III preferred conditioned leaves and animal food, while instar IV preferred algae and fine particulate organic matter. Gut contents of instar IV collected from streams showed increased consumption of fine particulate organic matter than other items. All these observations allowed us to assign the species to the gatherer collector group. The duration of the life cycle varied between the different types of foods, being the conditioned leaves, animal food, and algae the items that caused a greater growth in the larvae and a faster passage to the pupal instar. Our results suggest that the opportunistic feeding behavior of C. calligraphus allows it to use several different foods, but the quality of the foods influences the length of the life cycle and this contributes to its plasticity.

Effect Of The Quality Of Mulberry Leaves Morus alba Against The Silkworm Nutrition Index Bombyx mori L. (Lepidoptera:Bombicidae)

Th leaf quality effect of mulberry (Morus alba) on nutrition index of silkworm (Bombyx mori L.) has been studied. This research was design according to Completely Randomized Design (CRD) with 2 treatments which are an unfertilized mulberry plant, and the fertilized mulberry plants with urea, triple super phosphate (TSP), nitrogen, phosphor, and potassium (NPP). Twenty times replications was applied for each treatment. The results showed that the leaf of fertilized mulberry plant is evidently increased the growth and the consumption rate on the conversion efficiency of instar III, the feed digestion of instar V, the efficiency of food conversion of instar IV and V, and the estimate of feed digested of instar IV with the number for each was 36% and 26%, 30%, 34% and 67%, 24%, respectively.Bombyx mori L.

UJI EFEK LARVASIDA INFUSA BIJI SRIKAYA (Annona squamosa L.) TERHADAP LARVA Aedes aegypti

Indonesia as a tropical country has optimal humidity and temperature that are favorable for survival, larval growth, and disease transmission. One of them is dengue hemorrhagic fever (DHF). The use of chemical insecticides does provide effective and optimal results in eradicating disease-causing vectors. So that control is carried out with biological (vegetable) insecticides which are safer, simpler and environmentally friendly. One of the most effective plant-based insecticides against Aedes aegypti larvae is sugar apple or Annona squamosa L. which is effective as a stomach poison and contact poison because of its active ingredients, namely annonain and squamosin. This study aims to determine the effect of larvicidal infusion of srikaya seeds (Annona squamosa L.) on Aedes aegypti larvae. The object of this research is 40 larvae of Aedes aegypti instar IV. Aedes aegypti larvae were exposed to infusion of Annona squamosa L. seeds for 16 hours with well water as a negative control and abate as a positive control. Data analysis used regression analysis to determine the effect of infusion on larvae and probit analysis to determine LC50.The results of this study showed that the infusion of Annona squamosa L. seeds had a killing power of Aedes aegypti larvae of p=0.001 with a straight line equation Y=9.095+67.143X. Probit analysis showed that LC50. is 17%. Meanwhile, Annona squamosa L. seed infusion was not as effective as abate.Conclusion: The infusion of Annona squamosa L. seeds has the power to kill Aedes aegypti larvae, LC50. The concentration of Annona squamosa L. seed infusion to kill Aedes aegypti larvae after 16 hours of treatment was at a concentration of 17%, and abate was more effective than Annona squamosa L. seed infusion.

Salinity tolerance of larvae Aedes aegypti inland and coastal habitats in Pasangkayu, West Sulawesi, Indonesia

Abstract. Ratnasari A, Jabal AR, Syahribulan, Idris I, Rahma N, Rustam SNRN, Karmila M, Hasan H, Wahid I. 2021. Salinity tolerance of larvae Aedes aegypti inland and coastal habitats in Pasangkayu, West Sulawesi, Indonesia. Biodiversitas 22: 1203-1210. Aedes aegypti L. is the primary arboviral vector generally found in freshwater, but it is also observed in brackish water. The study analyzes habitat characteristics, larvae adaptation, and oviposition preference in salinity levels over the coastal and inland ecosystem in Pasangkayu District of West Sulawesi. The larvae were reared until adults and have larval of first progeny were examined the salinity tolerance in five salinity levels. Ovitrap-based experiments were carried out in the laboratory using adult Ae. aegypti colonies from inland and coastal areas. Eggs on filter paper (ovitrap) were identified and counted. Data were analyzed using LC50 (larvae with salinity tolerance) and Pearson correlation (correlation between the larvae phase two ecosystem factors). Total larvae observed in coastal areas and inland are 1437 and 1288, respectively. The salinity tolerance test showed that Instar IV is highly adapted to the saline environment. The larvae from the coastal (inland) area can tolerate salinity up to 13 (10) ppt. Mosquitoes can lay many eggs in 3 ppt salinity: 27.1% and 20.8% for coastal and inland colonies, respectively. Pearson correlation analysis showed a significant correlation between the larval instar stage of Ae. aegypti from coastal and inland ecosystems with the ability to survive at the salinity level (p < 0.01). This study is expected to be a source of information on the adaptation of Ae. aegypti mosquito to salinity in coastal and inland ecosystems. The findings can be considered in vector control efforts on brackish water habitats.

Chemical physical characteristics of Bombyx mori L C301 pupae under heat shock treatment

Bombyx mori pupae, the remaining of silk thread spinning contains a fairly high protein. Protein is not resistant to heat temperatures. Heat shock application causes failure of pupae formation and will affect the content of pupae organic compounds. Heat shock was given for 3 hours at 42°C when the larvae in instar IV, then the larvae were rearing until they become cocoons. Pupae was removed from the cocoon, then pupae morphology was observed. Analysis of pupae sampling includes protein, total fat and carbohydrates based on SNI 01-2891-1992.The failure of pupae formation was indicated by the blackish brown pupae and the irregular shape of the cocoon, while the pupae without heat shock was light brown.The content of silkworm pupae organic compounds that were given a heat shock was 80.4% protein.Total fat was 2.13% and carbohydrates were 6.58%. Heat shock did not affect the level of protein in pupae.

Studi Laboratorium Siklus Hidup Anopheles vagus Pradewasa sebagai Vektor Filariasis dan Malaria di Provinsi Nusa Tenggara Timur

Anopheles vagus is one of the vectors that plays an essential role in malaria infection in East Nusa Tenggara, Indonesia. This vector’s density is related to population dynamics and the environment. The high population density is fluctuated according to the birth and death rate of the mosquitos on their life cycle. This is an observational study that employed a cross-sectional design aimed to identify the life cycle of pre-adult An. vagus mosquitos. The sample was collected from Manggarai Barat and Kupang regions. Sample was taken from around cattle’s cages between 6.00pm-12.00am and were the ones that have sucked cattle’s blood. Identification and colonization were conducted in Loka Litbangkes Waikabubak Laboratory. Data was collected through an hourly observation form and then analyzed descriptively. The results indicated that an adult An.vagus could produce 42-184 eggs each time it laid eggs with 79% hatching rate succeed. The life cycle of an An.vagus under a controlled environment in the laboratory was as following phases: egg (1-4 days), larvae (9-19 days), pupa (1-8 days). Anopheles vagus needed an average of 57.2 minutes to mate and 13 hours to suck blood after the mating process. The highest death rate (28.05%) occurred in instar IVof larvae stage. Pre-adult of An. vagus needed 11-31 days in with the environment that conditioned at 21.1°C and 74.3% humidity for their development,while the highest death rate observed at instar IV.

MORPHOLOGICAL AND HISTOLOGICAL EFFECTS OF BRUCEINE A ON THE LARVAE OF AEDES AEGYPTI LINNAEUS (DIPTERA: CULICIDAE)

Objective: This study aimed to determine a target of action of bruceine A on the basis of its morphological and histological effects on the larvae of Aedes aegypti Linnaeus.Methods: Bruceine A was isolated from Brucea javanica (L.) Merr. seeds in accordance with the Mangungsong method. Larvae of A. Aegypti (L.) in instar III to the beginning of instar IV were treated with various concentrations of bruceine A. The negative control group did not receive any treatment, whereas the positive control group received 1 ppm temefos. Dead larvae were collected after 24 h of treatment for the examination of morphological and histological changes.Results: The negative control group did not exhibit any morphological and histological changes. Larvae treated with bruceine A, however, had visible damaged heads, cuticles, digestive and respiration tracts, respiratory siphons, and setae, and they were smaller than normal larvae. Larvae treated with temefos exhibited gastrointestinal damage, narrowed breathing tubes, cuticle damage, and detached/damaged seta feathers. The necrosis of gastrointestinal epithelial cells was the major histological change exhibited by larvae treated with various concentrations of bruceine A or 1 ppm temefos.Conclusion: The targets of action of bruceine A in A. aegypti (L.) larvae are the head/caput, cuticle, setae, siphon, and gastrointestinal and respiratory tracts.

Pre-emergence growth and development in the arctic midge Trichotanypus alaskensis Brundin

Developing at low mean temperatures, arctic chironomids often have prolonged larval growth yet adult emergence is typically a brief and highly synchronous event. How does a midge population achieve synchronous emergence? Under the Absolute Spring Species Hypothesis (AbSS), adult eclosion by early-emerging species may be synchronized by overwintering as fully mature larvae. Such prepupal larvae would neither feed nor grow after spring thaw, only pupate and emerge. The podonomine Trichotanypus alaskensis Brundin is an abundant midge in tundra ponds on Alaska’s Arctic Coastal Plain, and one of the earliest-emerging species in this chironomid-dominated insect community. T. alaskensis is univoltine in these arctic ponds, with most emergence from any one pond occurring within less than a one-week span during late June, typically about three weeks after pond thaw. We evaluated T. alaskensis for conformity to the AbSS model by documenting the overwintering state of this species in a tundra pond near Barrow, Alaska, then monitoring larval growth and development of the population from spring thaw to pupation. Most T. alaskensis were immature instar IV larvae when collected in late September of both 2010 and 2011, with 10-30% still in late instar III. Immediately after pond thaw in 2011, all collected larvae had imaginal disc primordia showing early stages of instar IV development. Within the first two weeks following pond thaw, most larvae had doubled their dry mass and developed into mature (prepupal) final-instar larvae. Highly synchronized emergence by T. alaskensis is not a consequence of a population overwintering as fully-mature larvae, as per the Absolute Spring Species Hypothesis. Rather, larvae in a given tundra pond appear to develop synchronously throughout the life cycle, including a period of substantial growth and rapid prepupal development between spring thaw and early-summer emergence.

Breaking the rule: Five larval instars in the podonomine midge Trichotanypus alaskensis Brundin from Barrow, Alaska

Except for one unconfirmed case, chironomid larvae have been reported to pass through four larval instars between egg and pupal stages. We have observed a fifth larval instar to be a standard life-cycle feature of the podonomine Trichotanypus alaskensis Brundin 1966 in tundra ponds on the Arctic Coastal Plain near Barrow, Alaska. T. alaskensis has a one-year life cycle in these arctic ponds. Adults emerge in June ~2-3 weeks after pond thaw, then mate and oviposit; most newly-hatched larvae reach instar IV by October when pond sediments freeze. Overwintering larvae complete instar IV within a few days of thaw, then molt again to a fifth larval instar. Imaginal discs, normally seen only during instar IV in Chironomidae, develop across both instars IV & V prior to pupation and adult emergence. While monitoring larval development post-thaw in 2014, we noticed freshly-molted T. alaskensis larval exuviae a week or more prior to any pupation by that species. In 2015-16 we reared overwintering instar IV larvae from single pond sources, individually with daily monitoring, through molts to instar V, pupa, and adult. Some overwintering instar II and III larvae were reared as well, but were few in number. During 2016 we also reared T. alaskensis progeny (from eggs) through instar II, thus documenting head capsule size ranges for all five instars in a single pond’s population. Without individual rearings, the fifth larval instar was not readily apparent for two reasons: 1) The molt itself occurs immediately after thaw and is so synchronous it is difficult to discern in daily field samples. 2) The head capsule size increment between instars IV-V is much lower than the ratio predicted by the Brooks-Dyar Rule. Up through instar IV, the Brooks-Dyar ratio for T. alaskensis ranged 1.30-1.61, but during the IV-V molt head capsule dimensions (sexes pooled) increased by a ratio of 1.09 – comparable to the magnitude of sexual dimorphism in head capsule size within each of the final two larval instars. Individual rearings coupled with 2014-2016 field surveys in nine other ponds suggest that five larval instars is an obligatory trait of this species at this location. As this is the first confirmed case of five larval instars in a chironomid, the phylogenetic uniqueness of this trait needs further investigation.

Larvicidal Activity of Bruceine A against Aedes aegypti and Toxicity on Vero Cells

Vector control is still based on the use of chemical insecticides, which can cause death of nontarget animals, pollution and the emergence of vector resistance. This study aims to assess the larvicidal activity of bruceine A against larvae of Aedes aegypti and its cytotoxic activity against Vero cells. Extraction and isolation of bruceine A from the seeds of Brucea javanica (L.) Merr by method of Subeki. The purity of bruceine A isolate is determined by using a thin layer of chromatography and high performance liquid chromatography. Larvicidal activity of bruceine A on the larvae of A. aegypti from instar III until the beginning of instar IV was measured using a bioassay method. The examination of bruceine A cytotoxicity on Vero cells was performed by Micro-culture Tetrazolium assay (MTT). The results showed that mortality of A. aegypti larvae increased with increasing concentration of bruceine A. Log probit analysis of the larva mortality showed that the lethal concentration 50 and 90 (LC50, LC90) were 0.453±0.022 ppm and 4.962±0.681 ppm for 24 h respectively. The cytotoxic activity of bruceine A in Vero cells is low, with inhibitor concentration 50 (IC50) values of 1251.324±0.162 µg/mL. Bruceine A has larvicidal activity against A. aegypti; therefore, it is a potential natural larvicide with low cytotoxicity.

Prolonged maturation time in female Caprella acanthogaster (Crustacea, Amphipoda) at low temperature under laboratory conditions

Caprellids are epifaunal crustaceans, widely distributed in marine environments. The life histories of many temperate caprellids have been described, but the growth pattern of a boreal species has not previously been observed. To fill this gap, a boreal species, Caprella acanthogaster, was reared at 5℃ under laboratory conditions and observed it from hatching to maturation and oviposition. Males were recognizable from instar IV and females from instar V. Female maturation was observed at instar VIII (115 days) and instar IX (126 days), whereas males did not mature morphologically in this study. The females matured at instar IX and oviposited subsequent to molting. These periods from hatching to maturation and oviposition are the longest known among previously reared female caprellids. Caprellids are known to mature rapidly in temperate regions. However, female C. acanthogaster required 4 months to mature at 5℃ while males need an even longer but unknown period. These observations at a low temperature fill a gap in the current information on caprellid life histories.

Study of the embryogenesis of Dunhevedia crassa King, 1853 (Cladocera: Chydoridae) and a comparison of embryonic instar durations in different cladocerans

The aim of this work is to study the embryonic development of a common tropical cladoceran Dunhevedia crassa King, 1853 (Anomopoda: Chydoridae) and compare the durations of embryonic instars and growth during embryogenesis in small-sized chydorids and other cladocerans. The sequence of events in the embryogenesis of Dunhevedia females was studied by means of i n vitro observation in the laboratory at 28.5°C. We found that the general pattern of the sequence of events in chydorid embryogenesis is similar to that in other anomopods. However, the relative durations of the embryonic instars I and II+III are markedly short, while that of instar IV is long (delayed) when compared with other cladocerans. The observed pattern of ontogenesis in chydorids may therefore be apomorphic within the cladocerans and could reflect a neotenic evolution. Another peculiar trait of Dunhevedia is the very small increase of the size of the embryo during embryogenesis, which is correlated with a very large size of the egg relative to the mother. Therefore, our study revealed some peculiarities in the ontogenesis of small-sized chydorids, which could be a result of family-specific evolution.

Population decline and life‐cycle changes in a phantom midge (Chaoborus flavicans) after introduction of planktivorous fish

Summary Eurasian perch (Perca fluviatilis), a non‐native planktivorous fish species in western Norway, has been released into Lake Myravatn, which previously lacked planktivorous fish. Prior to the introduction, the zooplankton community was structured by predation by larvae of the phantom midge (Chaoborus flavicans), which maintained a bivoltine life cycle in the lake. We hypothesised that the perch introduction would diminish the density and alter the bivoltine life‐cycle pattern of Chaoborus. To assess this, we used time series data from before (1983) and after (2007–10) the perch introduction. The perch appears to have effectively exterminated the previously dominant predator C. flavicans within 4–5 years of introduction into the lake. The density of the larvae in the water column was high in 1983 as well as in 2007, with maximum levels recorded in August (up to 15 400 individuals m−2). In 2008, larval density was lower than in previous years, but the most dramatic decline occurred in 2009 (maximum 212 individuals m−2). In 2010, the density was very low (maximum 11 individuals m−2), and after July 2010, no larvae were found in the water column. The number of larvae residing in the sediments also declined quickly after the perch introduction. In 1983 and 2007, C. flavicans produced two generations per year. Following the first emergence and reproduction in May, young larvae appeared in June and developed rapidly to emergence and reproduced again in August. Young larvae appeared again in August–September. In 2008, young larvae appeared only in June with no second emergence and reproduction. In 2009, young larvae did not appear until July, and again no further reproduction took place. Only a few instar IV larvae were recorded in 2010. The collapse in life cycle into a univoltine pattern occurred prior to the main population decline. We conclude that direct predation by perch on Chaoborus larvae is the most likely explanation for the observed changes in their life cycle and density. It appears that the C. flavicans population of Lake Myravatn is approaching extinction.

Postembryonic development and population parameters of Alpaida veniliae (Araneae, Araneidae), reared in the laboratory

We studied the postembryonic development from hatching to the adult stage and determined population parameters of Alpaida veniliae. It is one of the most abundant species of the orb-weaving guild of the spider community of soybean crops in Buenos Aires province, Argentina. The first three instars occurred inside the egg sac, and instar IV (spiderlings) started the dispersion from it. The female of Alpaida veniliae achieved greater adult size and adult longevity than the male. Mean fecundity, mean number of egg sacs per female, mean number of eggs per egg sac, as well as the net reproductive rate, the intrinsic rate of increase (r), the generation time (T), and the reproductive values (V x) of three cohorts were determined under laboratory conditions, indicating a high capacity for growth. Their biological and ecological attributes indicate the importance of conservation of this predator as a natural enemy of soybean crop pests.

Prepupal diapause and instar IV developmental rates of the spruce beetle, Dendroctonus rufipennis (Coleoptera: Curculionidae, Scolytinae)

The spruce beetle, Dendroctonus rufipennis (Kirby), is an important mortality agent of native spruces throughout North America. The life-cycle duration of this species varies from 1 to 3 years depending temperature. The univoltine cycle (one generation per year) is thought to maximize outbreak risk and accelerate host mortality in established outbreaks. Prepupal diapause is associated with the semivoltine cycle (one generation per 2 years) and we investigated thermal conditions that result in diapause induction. Preliminary experiments used respirometry in an attempt to distinguish the diapause state of experimental insects but the technique was apparently confounded by low respiration before and during pupation, regardless of diapause status. Therefore, diapause induction was deduced using developmental delays. The observed developmental response was not a “switch”, with developmental delay either present or absent, but instead varied continuously. We found that temperatures <15 °C from instar III through mid-instar IV were associated with developmental delays beyond that expected from cool temperatures. Moreover, the duration of exposure to cool temperatures was important in determining the degree of developmental delay. Small, if any, delays were observed if the cumulative exposure to <15 °C was <20 d whereas >40 d cumulative exposure was associated with distinct developmental suppression. Intermediate exposure to cool temperatures resulted in minor developmental delays. We used our results to parameterize a maximum likelihood estimation model of temperature-dependent instar IV developmental rates, including the effect of diapause. This model can be included as part of a spruce beetle phenology model for predicting population dynamics.

Impact of Chaoborus flavicans ‐Predation on the Zooplankton in a Mesotrophic Lake – a Three Year Study

AbstractThe predatory impact of Chaoborus flavicans on zooplankton, especially on daphniids, is often regarded as a crucial factor in the propagation or repeal of top‐down effects in lakes. Therefore consumption rates and prey selectivity of C. flavicans were determined in mesotrophic Lake Großer Vätersee, where cladocerans were the dominant zooplankton prey and the predatory impact of fish towards C. flavicans and cladocerans was low. Two generations of the main predatory instar IV of C. flavicans appeared in the pelagial, the first in autumn and the second in spring after having over wintered in the sediment. In discrepancy to the abundances, only the autumn generation showed high peaks of consumption. C. flavicans fed preferentially on medium‐sized cladocerans, but mostly disregarded daphniids and rotifers. Copepods were only selected when cladocerans were not present. The highest losses due to Chaoborus predation were found in Bosmina longirostris, Bosmina coregoni and Chydorus sphaericus. There was no evidence that the predatory impact of C. flavicans on daphniids substantially influenced lower trophic levels. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Ontogeny of Deeveya medix Kornicker, 1990, collected in anchialine and marine caves in the Bahama Islands (Ostracoda: Halocypridae: Deeveyinae)

Abstract Four juvenile instars of Deeveya medix (Instars I, II, III, and V) from marine caves and blue holes in the Bahamas are described and illustrated. The ontogeny of the species is compared with that of D. spiralis Kornicker & Iliffe, 1985, and D. bransoni Kornicker & Palmer, 1987 and found to be similar. Criteria are presented for identifying stages of species of Deeveya. Each lamella of the furca of known species of Deeveya bears 3 claws on instar I, 4 on instar II, 5 on instar III, 6 on instar IV, and 7 on instar V and the adult.

Ciclo de vida de Euschistus rufimanus (Stall) (Hemiptera : Pentatomidae) plaga del maíz en los Llanos Orientales de Colombia

El maíz es un producto importante en la Altillanura colombiana por su gran potencial económico en la agroindustria de alimentos concentrados para animales. No obstante, el cultivo se ve afectado por insectos plaga entre los que cuenta la Chinche café, Euschistus rufimanus (Stall) (Hemiptera : Pentatomidae), insecto que provoca deformación y disminución del área foliar de las hojas jóvenes, pérdida de la dominancia apical, macollamiento, esterilidad y muerte de la planta. El presente estudió determinó el ciclo biológico de E. rufimanus bajo condiciones de casa malla, temperatura de 28°C ± 2°C y humedad constante del 75%. A tal fin se colectó una población de adultos de la Chinche en un cultivo comercial de la Altillanura y se estableció una colonia. La duración de huevo a adulto fue de 43,5 días. La duración promedio de los estadios en días fue: huevo (4,88 ± 0,1); ninfa de primer instar (3,6 ± 0,1); ninfa de segundo instar (8,5 ± 0,5); ninfa de tercer instar (8,17± 0,5); ninfa de cuarto instar 7,70 ± 0,54; ninfa de quinto instar 10,5 ± 0,6, siendo el segundo el de mayor mortalidad (60,68%). La longevidad promedio fue de 74,5 ± 4,8 días para los machos y 77,5 ± 5,6 para las hembras. La duración promedio de la fase de preoviposición fue 8,32 ± 1,18 días y la de precópula fue 7,6 ± 1,1 días. El número promedio de posturas por hembra fue de 32,24 y el promedio de huevos por postura de 77,1 ± 10,8. Estos conocimientos servirán de fundamento para el desarrollo de estrategias de manejo integrado de plagas.

First year growth in the lithodids Lithodes santolla and Paralomis granulosa reared at different temperatures

The southern king crab, Lithodes santolla Molina, and stone crab, Paralomis granulosa Jacquinot, inhabit the cold-temperate waters of southernmost South America (southern Chile and Argentina), where stocks of both species are endangered by overfishing. Recent investigations have shown that these crabs show life-cycle adaptations to scarcity of food and low temperatures prevailing in subantarctic regions, including complete lecithotrophy of all larval stages and prolonged periods of brooding and longevity. However, growth and development to maturity are slow under conditions of low temperatures, which may explain the particular vulnerability of subpolar lithodids to fisheries. In the present study, juvenile L. santolla and P. granulosa were individually reared in the laboratory at constant temperatures ranging from 3–15 °C, and rates of survival and development through successive instars were monitored throughout a period of about nine months from hatching. When the experiments were terminated, L. santolla had maximally reached juvenile instar IV (at 6 °C), V (9 °C), or VII (15 °C). In P. granulosa the maximum crab instar reached was II (at 3 °C), V (6 °C), V (9 °C), or VII (15 °C). The intermoult period decreased with increasing temperature, while it increased in successively later instars. In consequence, growth rate showed highly significant differences among temperatures (P<0.001). Growth-at-moult was highest at 9 °C. Rates of survival decreased significantly in juvenile P. granulosa with increasing temperature. Only at 15 °C in L. santolla, was a significantly enhanced mortality found compared with lower temperatures. Our results indicate that juvenile stages of L. santolla and P. granulosa are well adapted to 5–10°C, the range of temperatures typically prevailing in subantarctic marine environments. In spite of causing higher mortality rates, higher rearing temperatures (12–15 °C) should accelerate the rates of growth and maturation, which may be favourable for projects aiming at aquaculture or repopulation of overexploited king crab stocks.