Larval Dry Weight Research Articles

Feed-shifting strategy for increasing biodiesel production from black soldier fly larvae

The aim of this study was to increase the bioconversion efficiency (lipid accumulation) of black soldier fly larvae while simultaneously increasing biodiesel production through a feed-shifting strategy. Feeding with low-lipid feed promoted an increase in larval weight, while high-lipid feed resulted in greater lipid accumulation. Based on this result, a feed-shifting strategy was introduced, which consisted of two stages: first, increasing larval body weight using low-lipid feed, followed by lipid induction for biodiesel production using high-lipid feed. The use of this strategy resulted in an increase in the dry weight of larvae by ≥16 % compared to single feeding systems. This led to a 20 % increase in biodiesel productivity. The waste reduction ratio was enhanced due to the higher bioconversion rate in the feed-shifting strategy compared to that in the single feeding systems. The feed-shifting strategy would contribute to the enhancement of waste-to-energy efficiency.

Categorization of resistance against the fall armyworm, Spodoptera frugiperda (J.E. Smith) in select maize inbred lines

Seven maize inbred lines were evaluated for resistance against fall armyworm, Spodoptera frugiperda (J.E. Smith). Non-preference for oviposition in no- and multi-choice tests and feeding non-preference of neonates in multi-choice test was observed in lines CML 338, CM 500 and CML 72. Antibiosis was observed in CML 338, CML 72 and CML 71, in terms of significantly prolonged larval period (18.22–19.56 days), lower larval (111.52–131.80 mg) and pupal weights (105.65–127.67 mg), shorter adult longevity and lower fecundity as compared to susceptible inbred lines, BML 6 and LM 24. Larvae fed on CML 338 and CML 71 had significantly higher mortality and lower nutritional indices. Significantly higher foliar damage rating was observed on younger plants (10 days old) in all test inbred lines, as compared to older plants (20 and 30 days old) during 2020 and 2021. The mean foliar damage rating by fall armyworm larvae varied significantly among the test inbred lines being significantly lower in CML 338 and CML 71 compared to BML 6 and CM 500 that had higher damage at all crop stages when recorded at 7, 14 and 21 days after release. Functional Plant Loss Index (FPLI) was significantly lower in CML 338 and CML 71 (12.18–18.58%) followed by CML 72 (24.87%). Regression of FPLI on fall armyworm larval dry weight indicated presence of antibiosis and tolerance in CML 338, CML 71 and CML 72 towards fall armyworm. Overall, maize inbred lines CML 338, CML 71 and CML 72 with moderate resistance may be used for resistance breeding programme against this insect pest.

Heritability of fat accumulation in the house fly and its implication for the selection of nutritionally tailored phenotypes

Abstract Fats make up a large fraction of the larval biomass in insects and are of increasing relevance for industrial purposes. The quantity of fats accumulated during the larval period can vary greatly among individuals. To selectively breed favourable fat accumulation phenotypes for commercial purpose, a genetic component underlying these differences would be required. In this study we determined the heritability of larval fat accumulation in the common housefly (Musca domestica L.). A nested paternal half-sib breeding design resulted in a total of 47 full-sib families, which produced in total 633 larvae, each phenotyped for their dry weight and fat content (absolute and relative). Adult selection was strictly standardized to reduce the variation in fat content induced by differences in development time during the immature stages: sires and dams were separated according to their pupation day and emergence day, and subsequently pooled into randomized groups. Two animal models were built to estimate the heritability of larval fat accumulation: (1) a Markov Chain Monte Carlo linear mixed model (MCMCglmm) where three sets of priors were used, and (2) one based on linear mixed model using restricted maximum likelihood (ASReml). The results showed a moderate heritability for larval absolute fat content for both MCMCglmm (between 0.30 and 0.38, depending on the set of prior used) and ASReml (0.37 ± 0.11). Slightly higher estimates were obtained for the relative fat content with both the MCMCglmm (between 0.34-0.48) and ASReml (0.47 ± 0.10). In contrast, heritability estimates for larval dry weight were low and could be obtained only with the MCMCglmm model (between 0.11-0.22). This work provides valuable insights into the quantitative genetics of larval fat characteristics, a trait of high relevance for the emerging sector producing insects for feed and food.

Lipid quantity and composition vary between three European house fly strains

AbstractLipids are an important class of nutrients for insects, as they are the main energy source during metamorphosis and crucial for survival and reproduction. Lipid reserves in insects are mostly accumulated during larval development and can be influenced by environmental factors such as diet and temperature. Genetic factors can also affect larval lipid content and composition. Larvae of the house fly, Musca domestica L. (Diptera: Muscidae), are a valuable emerging resource for the insect feed sector, fueling a growing interest in the factors regulating larval lipid content. We investigated whether strains of three geographical origins vary in ontogeny, quantity, and composition of stored lipids in response to temperature. Italian, Spanish, and Dutch house fly larvae were reared on a similar diet at 25 and 35 °C. Larval dry weight and total lipid content were determined in early‐, mid‐, and late‐third instars by extraction of soluble lipids. The fatty acid composition was analyzed in late‐third instars using an improved extraction and derivatization protocol. We found that strain, larval stage, and temperature affected larval dry weight and absolute and relative lipid content, with significant interaction effects between these three factors. All flies were reared in a common environment, indicating a genetic component to lipid storage. Analysis of lipid composition identified 11 fatty acids, including some rarely reported in the literature. Five fatty acids accounted for 80 and 81% of the total fatty acid methyl esters detected at 25 and 35 °C, respectively. An effect of temperature but not strain was evident on the composition of the fatty acids. The observed differences in lipid content among strains and temperature conditions could be of interest for commercial rearing of the house fly.

Growth, survivorship, and predator avoidance capability of larval shortnose sturgeon (Acipenser brevirostrum) in response to delayed feeding.

Larval shortnose sturgeon, reared at 17°C, were subjected to delayed feeding treatments of 0, 5, 10, 15, 18, and 23 days post-yolk absorption to examine effects of food deprivation on growth, survival, swimming activity, and escape capabilities. Starvation affected growth and survival but despite degree of starvation, larvae were able to resume growth and experience high survivorship following feeding. Specific growth rate based on larval dry weight for the period directly following first feeding was highest for the day 15 and 18 delayed feeding treatments. There were no differences in survival between the 0 and 5 day treatments, however survival was reduced to 71.2%, 45.4%, and 28.8% for 10, 15, and 18 day delayed feeding treatments, respectively. Shortnose sturgeon had a point-of-no-return (PNR; 55.7% initiated feeding) at ~19 days (or 42 days post-fertilization) following the full absorption of yolk. Mean percent swimming activity and swimming speeds showed an interaction between delayed feeding treatment and larval age, such that no differences were detected at 1 and 6 days post-yolk absorption, while these swimming behaviors generally increased or spiked as feeding was delayed for 10, 15, and 18 days post-yolk absorption. At 23 days post-yolk absorption, only swimming speed increased for larvae that were denied food for 18 days. While there was an interaction between delayed feeding treatments and age for proportion of larvae exhibiting an escape response, generally, larvae from all feeding treatments exhibited a positive escape response. There were also interactions between delayed feeding treatments and age post-yolk absorption for mean and maximum escape speeds, such that less aggressive escape responses were typically detected the longer larvae were denied food. Our research suggests that larval shortnose sturgeon increase physical activity during periods of starvation to find a food patch while remaining vigilant but maybe not as capable to defend against a predatory attack as fed individuals.

Variable shrimp in variable environments: reproductive investment within Palaemon varians

The maternal environment may influence the quantity and quality of resources invested in offspring (per-offspring provisioning) and this trait, in turn, affects larval fitness and may carry-over into early juvenile life. Here, per-offspring investment was measured across three consecutive breeding seasons for the caridean shrimp, Palaemon varians. Egg and hatchling larval dry weight as well as hatchling larval biochemical composition were measured. Results indicate that egg volume is positively correlated with dry weight, but egg volume as a proxy for dry weight should be used with caution. Correlations were identified between per-offspring investment and average breeding season temperature, but the period over which temperature was averaged was important to whether these correlations were positive or negative, highlighting the complexity of identifying environmental influence on phenotypic traits. The most important factor determining offspring size and per-offspring investment was maternal size, which may be influenced by the environment as carapace length varied significantly between breeding seasons. These data demonstrate variation in egg and larval composition, related to maternal size, which will affect early life traits and survivorship for P. varians.

First estimates of metabolic rate in Atlantic bluefin tuna larvae.

Atlantic bluefin tuna is an iconic scombrid species with a high commercial and ecological value. Despite their importance, many physiological aspects, especially during the larval stages, are still unknown. Metabolic rates are one of the understudied aspects in scombrid larvae, likely due to challenges associated to larval handling before and during respirometry trials. Gaining reliable estimates of metabolic rates is essential to understand how larvae balance their high growth needs and activity and other physiological functions, which can be very useful for fisheries ecology and aquaculture. This is the first study to (a) estimate the relationship between routine metabolic rate (RMR) and larval dry weight (DW) (mass scaling exponent) at a constant temperature of 26°C, (b) measure the RMR under light and darkness and (c) test whether the interindividual differences in the RMR are related to larval nutritional status (RNA/DNA and DNA/DW). The RMR scaled nearly isometrically with body size (b = 0.99, 0.60-31.56 mg DW) in contrast to the allometric relationship observed in most fish larvae (average b = 0.87). The results show no significant differences in larval RMR under light and darkness, suggesting similar larval activity levels in both conditions. The size explained most of the variability in RMR (97%), and nutritional condition was unrelated to the interindividual differences in routine metabolism. This is the first study to report the metabolic rates of Atlantic bluefin tuna larvae and discuss the challenges of performing bioenergetic studies with early life stages of scombrids.

Burying Beetle (Coleoptera: Silphidae: Nicrophorus Fabricius) Brooding Improves Soil Fertility

Burying beetles (Coleoptera: Silphidae) utilize the nutrients in vertebrate carrion to reproduce. The beetles utilize the bodies of rodents and birds as a reproductive resource by burying and preparing them with secretions. Although the importance of carrion to forest and savanna soil fertility has been documented, the benefit of burying beetle brooding behavior on soil nutrients has not. Native prairie soils are among the most fertile in the world, resulting in widespread agricultural conversion. Fire suppression, allowing the spread of eastern redcedar (Juniperus virginiana L., Pinales: Cupressaceae), intense grazing, and the introduction of non-native vegetation has reduced numbers of burying beetles and potentially impacted nutrient cycling by these species. A laboratory experiment was conducted using the burying beetle Nicrophorus marginatus F. to test the influence of carcasses, beetles, and their brood on soil nutrients. Soil was placed in a 4.3-L container and treated with rat carcasses, eastern redcedar needles, and pairs of adult burying beetles. Burial success, number and weight of larvae produced, and changes to soil nutrients were recorded. Rat carcasses buried manually increased soil pH, soluble salts, and available nitrate, phosphorus, and potassium content. Beetles and their larvae increased soil nutrients far more than the manually buried rat carcasses alone. Cedar needles did not affect adult survival, brood number, or soil nutrients, although larval dry weights were significantly less in soils with cedar needles. Burying beetles and their brood increase key nutrients for plant health in native soils and are not affected by eastern redcedar needles.

Baseline Susceptibility of a Laboratory Strain of Northern Corn Rootworm, Diabrotica barberi (Coleoptera: Chrysomelidae) to Bacillus thuringiensis Traits in Seedling, Single Plant, and Diet-Toxicity Assays

The northern corn rootworm (NCR), Diabrotica barberi Smith & Lawrence, is an economic pest of maize in the U.S. Corn Belt. The objective of this study was to determine the baseline susceptibility of a laboratory NCR strain to Bt proteins eCry3.1Ab, mCry3A, Cry3Bb1, and Cry34/35Ab1 using seedling, single plant, and diet-toxicity assays. Plant assays were performed in greenhouse using corn hybrids expressing one of the Bt proteins and each respective near-isoline. Diet-toxicity assays, consisting of Bt proteins overlaid onto artificial diet were also conducted. In both plant assays, significantly more larvae survived Cry34/35Ab1-expressing corn compared with all other Bt-expressing corn, and larvae that survived eCry3.1Ab-expressing corn had significantly smaller head capsule widths compared with larvae that survived Cry34/35Ab1-expressing corn. In seedling assays, larvae surviving eCry3.1Ab-expressing corn also had significantly smaller head capsule widths compared with larvae that survived mCry3A-expressing corn. Additionally, larvae that survived mCry3A-expressing corn weighed significantly more than larvae surviving eCry3.1Ab- and Cry34/35Ab1-expressing corn. In single plant assays, no significant differences in larval dry weight was observed between any of the Bt-expressing corn. In diet assays, LC50s ranged from 0.14 (eCry3.1Ab) to 10.6 µg/cm2 (Cry34/35Ab1), EC50s ranged from 0.12 (Cry34/35Ab1) to 1.57 µg/cm2 (mCry3A), IC50s ranged from 0.08 (eCry3.1Ab) to 2.41 µg/cm2 (Cry34/35Ab1), and MIC50s ranged from 2.52 (eCry3.1Ab) to 14.2 µg/cm2 (mCry3A). These results establish the toxicity of four Bt proteins to a laboratory diapausing NCR strain established prior to the introduction of Bt traits and are important for monitoring resistance evolution in NCR field populations.

Quality Aspects of Insects as Food-Nutritional, Sensory, and Related Concepts.

In the search for another appealing source of future food to cover the increasing need for nutrients of a growing global population, this study reviewed the potential of insects as human food. Most previous reviews have dealt with insects as a group, making it difficult to evaluate each individual insect species as food because of the generalized data. This study assessed some common edible insects, but concentrated on mealworms. Insects, especially mealworms, have a similar or higher nutritional value than many conventional food sources. For example, the protein content of mealworm larvae is reported to be almost 50% of dry weight, while the fat content is about 30% of larval dry weight. Mealworms can be cooked by different methods, such as hot air drying, oven broiling, roasting, pan frying, deep frying, boiling, steaming, and microwaving. Oven broiling in particular gives a desirable aroma of steamed corn for consumers. Changes in the flavor, taste, and texture of mealworm products during storage have not been studied, but must be determined before mealworms can be used as a commercial food source. Factors controlling the shelf-life of mealworms, such as their packaging and storage, should be identified and considered with respect to the feasibility of using mealworms on a commercial scale.

Performance of Mixed Species and Mono‐specific Algal Diets for Culture of Larval Western School Prawns, Metapenaeus dalli

AbstractThe effect of three mono‐specific and four combinations of the diatoms Chaetoceros muelleri, Chaetoceros calcitrans, and the chlorophyte Tetraselmis suecica on survival, development, and dry weight of the western school prawn, Metapenaeus dalli, was assessed from protozoea I until mysis I. The development and dry weight of larvae were significantly greater when fed diets comprising C. muelleri and/or T. suecica. A fourth diet, consisting of all three microalgal species also performed just as well. Survival alone was a poor measure of the performance of the various diets. Larvae fed with C. calcitrans, either alone or in a mixed diet with either C. muelleri or T. suecica, had significantly slower development and lower dry weight. Overall performance, assessed using the normalized biomass development index, determined that both mono‐specific and mixed diets containing C. muelleri and T. suecica were among the best for M. dalli larvae. These results for M. dalli are consistent with those found for commercially grown penaeid prawns. This study enhances the limited knowledge on the feeding requirements of metapenaeid prawn larvae. Moreover, the results will help improve hatchery methods for the aquaculture‐based enhancement of M. dalli in the Swan‐Canning Estuary and potentially increase the abundance of this iconic recreational species.

Sublethal Effects of vATPase-A and Snf7 dsRNAs on Biology of Southern Corn Rootworm, Diabrotica undecimpunctata howardi Barber.

RNA interference is a powerful tool against corn rootworm. Adults and neonates of southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), were exposed to the LC50 of vATPase-A and Snf7 double-stranded RNAs (dsRNAs), and the effects on female fecundity, egg viability, male fitness as measured by sperm viability and mating capacity, larval recovery along with dry weight, and instar determination 10 d after exposure to dsRNA, were determined. Significant reductions were observed for a number of parameters in dsRNA-exposed rootworms relative to control treatments. Female fecundity and larval recovery were significantly reduced after exposure to both dsRNAs. In addition, larval dry weight and recovery of 2nd and 3rd instars along with dry weight for 3rd instars were significantly reduced after neonate exposure to vATPase-A dsRNA. Neither dsRNA affected male capacity to mate or sperm viability after exposure to the respective LC50s. After 10 d of feeding on untreated corn roots, neonates that survived exposure for 2 d to the vATPase-A dsRNA LC50 exhibited lower dry weight than the control. There was significant gene knockdown in adult males and females after exposure for 5 d to LC50 of vATPase-A and Snf7 dsRNAs. The parameters are discussed in terms of fitness and possible outcomes after deployment of corn hybrids expressing dsRNAs.

Comparing Na/K-ATPase activity of Macrobrachium rosenbergii (de Man) larvae at specific developmental stages, using different sodium vs potassium and calcium vs magnesium concentrations, and sodium potassium adsorption ratio (SPAR) mediums

The present study analyzed the Na/K-ATPase activity (μmolADP/mgprotein/h) of Macrobrachium rosenbergii larvae at specific developmental stages using different environmental concentrations of sodium vs potassium and calcium vs magnesium, for pairwise comparison. In addition, we also compared the effect of various sodium potassium adsorption ratio (SPAR) mediums to Na/K-ATPase activity. The first experiment compared the effect of sodium concentrations (4000 and 5000ppm) vs potassium concentrations (150 and 200ppm), while the second experiment compared the effect of calcium concentrations (180 and 240ppm) vs magnesium concentrations (300 and 400ppm), as in pairwise combination on the Na/K-ATPase activity. The third experiment compared Na/K-ATPase activity for various SPAR mediums (20, 30, 40 and 50). Larval condition index (LCI), larval dry weight and percent survival were determined at the 1st, 4th, 7th and 11th stages for each experiment. For each experimental treatment, triplicate 80-l closed-loop RAS systems were used. Initial larvae stocking density was 300 larvae l−1. For each container, a 40mg batch of larvae was collected at each of the 4 larval stages to analyze Na/K-ATPase activity and LCI. These results revealed that at the 1st and 4th larval stages both sodium and potassium independently and in combination, affected (P<0.05) Na/K-ATPase activity. However, at the 7th stage, enzyme activity was confirmed only among the treatments, independently. At the 11th stage, enzyme activity was demonstrated among the combined treatments, in addition to potassium, alone. Calcium and magnesium only showed larval Na/K-ATPase activity independently at the 1st and 4th larval stages. Results also showed that at the 1st and 4th larval stages, Na/K-ATPase activity was significantly higher for SPAR 20 but, at the 7th and 11th stages the enzyme activity was significantly higher at both SPAR 20 and 30. Accordingly, our findings have demonstrated that, Na/K-ATPase activity is highly variable during M. rosenbergii larval development and that it is mainly affected by interactions of common environmental macro-elements involved in larval osmoregulation. As such, we recommend M. rosenbergii hatcheries to operate as close as possible to SPAR 30 for early larval development and SPAR 40 for later larval development.

Antifeedant and Toxic Effect of Crude Extract from &lt;i&gt;Flourensia oolepis&lt;/i&gt; and their Impact on Nutritional Parameters of &lt;i&gt;Helicoverpa gelotopoeon&lt;/i&gt;

Botanical insecticides are one of the environmentally acceptable options for pest management. Extract of Flourensia oolepis (known as chilca), a plant endemic to the province of Córdoba, Argentina, has shown insecticidal activity. The aim of this work was to study the effect of crude extract of this F. oolepis on the nutritional parameters of Helicoverpa gelotopoeon, a polyphagous species recently reported as one of the most serious pests of chickpea. Choice tests were conducted using different doses of extract (1 to 10%) and acetone (control), and no-choice tests, feeding larvae for 10 days with chickpea leaves treated with extract (1 to 5%), with controls (water and acetone). We used three third instar larvae per replica and 8 repetitions of each. The variables measured were: consumption, fresh and dry weight of larvae, of feces and of the leaves given every 48 hours. We calculated the feeding inhibition and nutrition indices, and survival. In choice bioassays using the 10% dose, larvae preferred the control leaves, with the extract acting as a feeding inhibitor (92%). In the nochoice test, leaf consumption was markedly reduced with extract, affecting larval growth in a dose-dependent manner (p &lt; 0.05), as well as feed utilization and lepidoptera survival. © JASEMKeywords: Helicoverpa gelotopoeon; Flourensia oolepis; Botanical insecticides; Pest; Food utilization

High environmental salinity reduces the reproductive potential of the spider crab Maja brachydactyla (Decapoda, Majidae)

AbstractThe spider crab Maja brachydactyla is an important fisheries species in Europe. Adults were sampled in Ría de A Coruña (NW Spain) and transported to IRTA rearing facilities. Salinity and photoperiod changes and their effect on reproduction were tested in the laboratory. The number of newly hatched larvae per batch (presence of actively swimming newly hatched larvae in a broodstock tank) was counted and sampled to estimate dry weight and proximal composition. Keeping spider crab broodstock in a high salinity environment (38 ppt) significantly reduced the number of newly hatched larvae, reaching up to fivefold difference in winter. The number of newly hatched larvae produced under a natural photoperiod was 10‐fold higher than those produced using a fixed photoperiod at 34 ppt salinity during winter. No clear pattern of changes in larval dry weight, protein, lipid or carbohydrate composition was observed under the environmental conditions tested. The results show that the salinity used for broodstock maintenance, especially during the embryonic development, is an important factor causing changes in larval production of M. brachydactyla and with potential implications for recruitment success.

Sublethal mechanisms of Pb and Zn toxicity to the purple sea urchin (Strongylocentrotus purpuratus) during early development

In order to understand sublethal mechanisms of lead (Pb) and zinc (Zn) toxicity, developing sea urchins were exposed continuously from 3h post-fertilization (eggs) to 96h (pluteus larvae) to 55 (±2.4)μgPb/L or 117 (±11)μgZn/L, representing ∼70% of the EC50 for normal 72h development. Growth, unidirectional Ca uptake rates, whole body ion concentrations (Na, K, Ca, Mg), Ca2+ ATPase activity, and metal bioaccumulation were monitored every 12h over this period. Pb exhibited marked bioaccumulation whereas Zn was well-regulated, and both metals had little effect on growth, measured as larval dry weight, or on Na, K, or Mg concentrations. Unidirectional Ca uptake rates (measured by 45Ca incorporation) were severely inhibited by both metals, resulting in lower levels of whole body Ca accumulation. The greatest disruption occurred at gastrulation. Ca2+ ATPase activity was also significantly inhibited by Zn but not by Pb. Interestingly, embryos exposed to Pb showed some capacity for recovery, as Ca2+ATPase activities increased, Ca uptake rates returned to normal intermittently, and whole body Ca levels were restored to control values by 72–96h of development. This did not occur with Zn exposure. Both Pb and Zn rendered their toxic effects through disruption of Ca homeostasis, though likely through different proximate mechanisms. We recommend studying the toxicity of these contaminants periodically throughout development as an effective way to detect sublethal effects, which may not be displayed at the traditional toxicity test endpoint of 72h.

Influence of salinity on embryogenesis, survival, growth and oxygen consumption in embryos and yolk-sac larvae of the Nile tilapia

The Nile tilapia is a euryhaline species that offers considerable potential for culture in low-salinity waters. In order to investigate the ability of this species to be reared during the hatchery stages in brackish water, the effects of varying low salinities (0, 7.5, 15, 20 and 25ppt) on hatchability, survival, growth and energetic parameters until yolk-sac absorption were assessed. Salinity up to 20ppt was tolerable, although reduced hatching rates at 15 and 20ppt suggest that these salinities may be less than optimal. Optimum timing of transfer of eggs from freshwater to elevated salinities was 3–4h post-fertilisation, following manual stripping and fertilisation of eggs, however increasing incubation salinity lengthened the time taken to hatch. Dry body weight was related to salinity, with larvae in salinities greater than 15ppt displaying, at hatch, a significantly (GLM: ρ<0.05) lower body weight but containing greater yolk reserves than those in freshwater or lower salinities. Survival at yolk-sac absorption displayed a significant (GLM; ρ<0.05) inverse relationship with increasing salinity and mortalities were particularly heavy in the higher salinities of 15, 20 and 25ppt. Mortalities occurred primarily during early yolk-sac development yet stabilised from day 5 post-hatch onwards. Salinity had a negative effect on yolk absorption efficiency (YAE). Salinity-related differences in oxygen consumption rates were not detectable until day 3 post-hatch. Oxygen consumption rates of larvae in freshwater between 3 and 6days post-hatch were always significantly higher (GLM: ρ<0.05) than those in 7.5, 15, 20 and 25ppt, however, on day 9 post-hatch this pattern was reversed and freshwater larvae had a significantly lower QO2 than those in elevated salinities. Salinity had a significant inverse effect on larval standard length, with elevated salinities producing shorter larvae from hatch until day 6 post-hatch, after which time there was no significant differences between treatments. Salinity had a significant effect on whole larval dry weight, with heavier larvae in elevated salinities throughout the yolk-sac period (GLM; ρ<0.05).

Larval biomass and chemical composition at hatching in two geographically isolated clades of the shrimp Macrobrachium amazonicum: intra- or interspecific variation?

The shrimp Macrobrachium amazonicum (Heller 1862) has an extremely large geographic range (>4000 km across) in northern and central South America, comprising estuarine and fully limnic inland populations, which are hydrologically isolated from each other. Significant variations in ecology, physiology, reproduction, and larval development suggest an at least incipient allopatric speciation due to limited genetic exchange. In a comparative experimental investigation with shrimps from the Pantanal (upper Paraguay River basin) and the Amazon delta, respectively, we measured larval body size, dry weight (W), biochemical (total protein; lipid; fatty acids, FA), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN) at hatching. All these early larval traits are relevant for the degree of developmental dependence on planktonic food sources. Various consistent differences were observed between the two populations: Newly hatched larvae produced by shrimps from the Amazon delta were significantly smaller and showed lower values of W, CHN, protein, and unsaturated FA compared to those from the Pantanal. On the other hand, they contained significantly higher quantities of total lipid and saturated FA and, in consequence, higher ratios of lipid:protein, C:N, and saturated:unsaturated FA. All these differences in biomass and chemical composition suggest that the larvae of the Amazon population are energetically better adapted to planktonic food limitation, which likely occurs during riverine downstream transport toward coastal marine waters, also explaining previous observations of much stronger initial starvation tolerance in larvae from the Amazon versus those from the Pantanal. The latter develop in highly productive lentic inland waters, where large body size, an early onset of feeding, and a strong musculature (indicated by a high protein content) should facilitate their role as planktonic predators and allow for fast growth. An initial independence from food (lecithotrophy in the zoea I stage) as well as a preference for oligohaline rather than fully limnic conditions observed in the Pantanal larvae are interpreted as traits that have persisted from an ancestral coastal marine clade. Altogether, consistent ontogenetic differences between shrimps from the Pantanal and the Amazon estuary support the hypothesis that the taxon M. amazonicum comprises a complex of closely related but separate species.

Replacement of live prey by formulated diets in larval rearing of spider crab Maja brachydactyla

Preliminary experiments on the replacement in live prey by a formulated microbound diet (MBD) were carried out during larval development of the spider crab, Maja brachydactyla. Four levels (25, 50, 75 and 100%) of replacement of live prey (enriched Artemia metanauplii, EAM) were tested throughout larval development (zoea I = ZI, zoea II = ZII and megalopa = M). Replacement of up to 50% had no significant effect on the growth rate and survival of the larvae during any stage. Total replacement (100% MBD) resulted in a decrease in larval dry weight suggesting a poor assimilation of the proteins and lipids of the MBD. Survival of the larvae fed with the MBD did not appear to be affected, as it was significantly higher than the unfed control. Digestive enzyme activity (protease and amylase) of the larvae was probably influenced by both the physiological response to the formulated diet and larval ontogenetic changes. Further research is needed to improve MBD digestibility and to establish the lipid requirements of the larvae.

Bottom-up effects of Brassica napus nutrition on the oviposition preference and larval performance of Ceutorhynchus obstrictus (Coleoptera: Curculionidae)

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a serious pest of canola, Brassica napus L. and Brassica rapa L., both in Europe and North America. Nitrogen and sulfur levels can be readily manipulated by growers and could potentially be exploited to improve current pest management strategies. In an effort to better understand the relationship between host plant nutrition and C. obstrictus oviposition preference and its larval developmental biology, we exposed gravid females to host plants grown under differing regimes of nitrogen and sulfur. Results indicated that plants grown with a higher supply of nitrogen were preferred as hosts. Plants with a higher sulfur supply were also preferred but only in plants grown at lower nitrogen levels. In contrast, larval development time increased with increasing nitrogen levels although larval dry weights were unaffected. The results were inconsistent with the preference-performance hypothesis. The inconsistencies between oviposition choice and larval growth and development may be due to a conflict between maternal and larval fitness. Observed changes in larval development time may not represent a significant fitness cost for larval C. obstrictus, as no corresponding change in larval weight was observed. Possible causal mechanisms for the increase in development time include differences in oil, protein and glucosinolate contents of the seed. Fertilizer management regimes currently recommended were considered to be optimal for management of C. obstrictus as the yield benefits from higher rates of nitrogen fertilization would more than compensate for increased level of infestation.