Functional Characterization of an Odorant Receptor Expressed in Newly Hatched Larvae of Fall Armyworm Spodoptera frugiperda.

In the past decade, Spodoptera frugiperda has emerged as a significant invasive pest globally, posing a serious threat to agriculture due to its broad diet, migratory behavior, and ability to cause extensive plant damage. While extensive research has focused on the olfactory capabilities of adult S. frugiperda, understanding of the olfactory process in larvae remains limited, despite larvae playing a crucial role in crop damage. To address this gap, we identified an odorant receptor (OR), SfruOR40, expressed in the first-instar larvae through phylogenetic analysis. Using quantitative real-time PCR, we compared SfruOR40 expression levels in larvae and adults. We then characterized the function of SfruOR40 against 67 compounds using the Xenopus oocyte expression system and found that SfruOR40 responded to three plant volatiles. Further, behavioral experiments revealed a larval attraction to (-)-trans-Caryophyllene oxide. This study elucidates SfruOR40's role in the olfactory recognition of newly hatched S. frugiperda larvae, expanding our knowledge of such mechanisms in Noctuid moths. Furthermore, it highlights the potential of plant-derived natural products for biological pest control from a behavioral ecology perspective.

Effects of temperature on eggs and larvae of Anisakis simplex sensu stricto and Anisakis pegreffii (Nematoda: Anisakidae) and its possible role on their geographic distributions.

Effects of temperature on development of eggs, recently hatched larvae and L3 larvae of the marine parasitic nematodes Anisakis simplex sensu stricto (s.s.) and A. pegreffii were examined in vitro. The eggs of A. simplex s.s. hatched at 3-25 °C and those of A. pegreffii hatched at 3-27 °C. Days before hatching varied between 2 days at 25 °C and 35-36 days at 3 °C in A. simplex s.s. and between 2 and 3 days at 27 °C and 65 days at 3 °C in A. pegreffii. Hatching rates of A. simplex s.s. were maintained high at temperatures between 3 and 25 °C but decreased to 0% at 27 °C. In contrast, those of A. pegreffii were lowest particularly at 3 °C, but also at 27 °C. The mean 50% survivals of hatched larvae ranged from 5.3 days at 25 °C to 82.3 days at 9 °C in A. simplex s.s., while in A. pegreffii it ranged from 1.2 days at 27 °C to 77.2 days at 9 °C. L3 larvae of A. pegreffii exhibited higher survival rates and activity than those of A. simplex s.s., particularly at 20 and 25 °C. These results suggest that the early stages of A. simplex s.s. are more adapted to lower temperatures whereas those of A. pegreffii are more tolerant to warm environments, which may correspond to their distribution patterns in Japan and Europe.

Viability and development of Ascaridia galli eggs recovered in artificial media followed by storage under different conditions.

Eggs oviposited by Ascaridia galli females in artificial media are commonly used as a source of infective material. We investigated the rate of egg production by cultured mature females (n = 223), and changes in egg viability under different storage and incubation conditions. Eggs recovered after 1, 2 or 3 days of culture were subjected to either (1) storage in water at 4°C (1, 4 or 8 weeks) followed by incubation in 0.1 N H2SO4 at 26°C (2, 4 or 6 weeks); or (2) prolonged storage at 4°C (up to 14 weeks). Egg development and viability was assessed by morphology coupled with a viability dye exclusion test of hatched larvae. Of the 6,044 eggs recovered per mature female 49.2, 38.5 and 12.3% were recovered on days 1, 2 and 3 of worm incubation respectively with similar initial viability (≥99%) between days. Eggs recovered on different days had only minor differences in viability after storage. The prolonged storage period at 4°C significantly affected both viability and embryonation ability resulting in decline in viability of 5.7-6.2% per week. A smaller but significant decline in egg (2.0%) and hatched larval (1.4%) viability per week of incubation at 26°C was also observed. We conclude that storage and incubation conditions, not the day of egg recovery, are the main factors affecting A. galli egg viability. Our findings indicate that under aerobic conditions storage at 26°C may be preferable to 4°C whereas other studies indicate that under anaerobic conditions storage at 4°C is preferable.

The effects of temperature and dissolved oxygen on the growth, survival and oxidative capacity of newly hatched hybrid yellow catfish larvae (Tachysurus fulvidraco♀ × Pseudobagrus vachellii♂).

Demand for yellow catfish fry, an economically important farmed fish in China, has increased dramatically. Newly hatched larvae are highly sensitive to changes in environmental conditions, with water temperature (T) and dissolved oxygen (DO) being two important factors that affect their early development. We investigate optimal T (between 19.0 and 33.0 °C) and DO (between 2.0 and 12.0 mg L-1) concentrations on growth and antioxidant enzyme activity of newly hatched hybrid yellow catfish larvae (Tachysurus fulvidraco × Pseudobagrus vachellii) using a central composite design. We use a response surface method to optimize the response variables for survival (S) and growth, and the reduction of oxidative stress, over a 50-day experimental duration. T has a significant effect on specific growth rate (SGR), hepatic malondialdehyde (MDA) content, and superoxide dismutase (SOD) and catalase (CAT) activities (P < 0.05). DO concentration has a significant effect on SGR, S, hepatic MDA content, and SOD and CAT activities (P < 0.05). T and DO also have significant second order effects on SGR, S, SOD, and CAT activities (P < 0.05). Increased DO at low T stimulates SOD and CAT activities and alleviates oxidative damage. Adjusted R2 values for SGR, S, CAT, SOD, and MDA models are 0.734, 0.937, 0.916, 0.894 and 0.826, respectively. A combination of 26.8 °C and 7.3 mg L-1 represents optimal rearing conditions, in that larval growth and antioxidant ability is improved. Results show that T and DO during larviculture of yellow catfish have important implications for aquaculture.

Effects of different light spectra on embryo development and the performance of newly hatched turbot (Scophthalmus maximus) larvae.

Light is a key environmental factor that synchronizes various life stages from embryo development to sexual maturation in fish. For turbot, light spectra have the most influence at the larval and juvenile stages. In the current study, differences in the development of embryos and the performance of newly hatched turbot larvae exposed to five different spectra: full spectrum (LDF), blue (LDB, peak at 450 nm), green (LDG, peak at 533 nm), orange (LDO, peak at 595 nm) and red (LDR, peak at 629 nm), were examined. At 62.8 h post fertilization, a higher number of embryos exposed to short-wavelengths (LDG and LDB) had developed a heartbeat in comparison with embryos exposed to other wavelengths. Larvae exposed to the green spectrum had higher malformation rates than larvae exposed to the other spectra, indicating that larvae exposed to green light may have significantly reduced survival rates. The results of non-specific immunity parameters showed that the mRNA expression levels of cathepsin D (CTSD), cathepsin F (CTSF), catalase (CAT) and metallothionein (MT) in larvae exposed to LDB were significantly higher than those exposed to other spectra, but CAT activity in larvae exposed to LDB was significantly lower than larvae exposed to the other spectra. There was no significant difference in MT activity in larvae exposed to the five different spectra. The mRNA expression level of lysozyme (LZM) in larvae exposed to LDR was significantly higher than other spectra, while there was no significant difference in LZM activity observed in larvae exposed to LDR, LDG, LDB and LDF. The difference of the enzyme activity of total superoxide dismutase (T-SOD) was not significant among larvae exposed to the five spectra. mRNA expression of the heat shock protein 70 (HSP70) was significantly higher in newly hatched larvae exposed to LDB, LDR and LDG, indicating that larvae exposed to LDB, LDG and LDR exhibited a stress response. The mRNA expression level of the insulin-like growth factor-1 (IGF-1) and growth parameters in the newly hatched larvae exposed to the different spectra were not significantly different. The results of the present study indicate that LDO and LDF should be used for embryo incubation and newly hatched larvae when rearing turbot. This study provides a theoretical basis for optimizing the incubation light environment for fertilized turbot eggs, promoting immunity and reducing stress responses in newly hatched larvae.

LC-MS/MS-Based Metabolome Analysis of Biochemical Pathways Altered by Food Limitation in Larvae of Ivory Shell, Babylonia areolata.

Ivory shell, Babylonia areolata, is one of the commercially important mariculture species in China and South East Asia. Survival varies in the artificial hatching and larval rearing of B. areolata. Food deprivation may be involved in rearing mortality, and so, a better understanding of how larvae respond and adjust to starvation is needed. In this study, the metabolite profiles of newly hatched larvae with yolk (I), larvae with yolk exhaustion (II), larvae suffering 24 h starvation after yolk exhaustion (III), and larvae fed with exogenous nutrients after yolk exhaustion (IV) were analyzed by LC-MS/MS. Principal component and cluster analyses revealed differential abundance of metabolite profiles across groups. When compared to metabolite levels of the I group, significantly up-regulated metabolites included polyunsaturated fatty acids, phospholipids, nucleotide, amino acids, and their derivatives were found in the II group, indicating that organisms relied predominantly on glycerophospolipid metabolism and protein-based catabolism for energy production during this stage. During starvation after yolk exhaustion, the levels of all energy related metabolites were significantly reduced, but an increase in products of purine and pyrimidine metabolism indicated an insufficient energy supply and an increase in cellular disintegration. Larvae fed exogenous nutrients can have significantly improved metabolism compared to starved larvae. These findings suggest that metabolomics, using LC-MS/MS, can be used to assess the physiological status and food-affected metabolic changes affecting B. areolata larvae.

Ecotoxicological studies with newly hatched larvae of Concholepas concholepas (Mollusca, Gastropoda): bioassay with secondary-treated kraft pulp mill effluents.

The Chilean abalone or "loco" (Concholepas concholepas, Bruguière 1789) represent the most economically important marine recourse exploited from inner inshore Management and Exploitation Areas for Benthic Resources along the Chilean coast. In this study, newly-hatched larvae of C. concholepas were investigated as a potential model species for marine ecotoxicological studies. The study developed a behavioral standard protocol for assessing the impact that kraft pulp mill effluents after secondary treatment have on C. concholepas larvae. Under controlled laboratory conditions, newly-hatched larvae were exposed to a series of different concentrations of kraft pulp mill effluents with secondary treatment (Pinus spp. and Eucalyptus spp.), potassium dichromate as standard reference toxicant and effluent-free control conditions. Regardless of the type of effluent the results indicated that diluted kraft pulp effluent with secondary treatment had reduced effect on larval survival. Low larval survivals were only recorded when they were exposed to high concentrations of the reference toxicant. This suggests that C. concholepas larval bioassay is a simple method for monitoring the effects of kraft pulp mill effluents with secondary treatment discharged into the sea. The results indicated that dilution of ca. 1% of the effluent with an elemental chlorine free (ECF) secondary treatment is appropriate for achieving low larval mortalities, such as those obtained under control conditions with filtered seawater, and to minimize their impact on early ontogenetic stages of marine invertebrates such as newly-hatched larvae of C. concholepas. The methodological aspects of toxicological testing and behavioral responses described here with newly-hatched larvae of C. concholepas can be used to evaluate in the future the potential effects of other stressful conditions as other pollutants or changes in seawater pH associated with ocean acidification.