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Oviposition is an important event in the life cycle of mosquito which is a decisive factor for the fate of its progeny. If oviposition is prevented, the life cycle of mosquito is disrupted and the population growth can be reduced. Diethyl-phenylacetamide (DEPA) is an effective topical repellent against various haematophagous insects. The study reports the egg retention effect and subsequent lethal effect of DEPA on the gravid females of Aedes aegypti and Ae. albopictus mosquitoes. DEPA was applied at 1000 mg/l onto water surface in oviposition bowls under no-choice condition. Experiments had three replicates with three control and treated cages separately, containing 100 gravid females of each test mosquito species. Every day freshly treated oviposition bowls were provided to the gravid mosquitoes till the last surviving female of the cohort was dead. On completion of one experimental day (24 h) the number of eggs laid in control and treatment bowls were counted manually to assess the oviposition response and longevity of test mosquito species. DEPA at 1000 mg/l concentration reduced the egg deposition and affected the longevity of gravid females. In the DEPA treated cages >1100 eggs were retained by both the species. In the treated cages, about 50% of Ae. albopictus and 41% of Ae. aegypti females died, retaining eggs in their abdomen. The average life span of Ae. aegypti and Ae. albopictus females in control cages were 43 and 50 days respectively, while the females of both the species exposed to DEPA in treated cages survived for 16-22 days. Presence of DEPA odor on water surface forced the gravid Aedes females to retain their eggs, affecting their fecundity and longevity. This indigenously developed topical repellent DEPA may be applied to container's water that act as breeding grounds for dengue vectors to deter gravid females from oviposition in the vicinity of a household.

Evolutionary transitions from egg laying (oviparity) to live birth (viviparity) are common across various taxa. Many species also exhibit genetic variation in egg-laying mode or display an intermediate mode with laid eggs containing embryos at various stages of development. Understanding the mechanistic basis and fitness consequences of such variation remains experimentally challenging. Here, we report highly variable intra-uterine egg retention across 316 Caenorhabditis elegans wild strains, some exhibiting strong retention, followed by internal hatching. We identify multiple evolutionary origins of such phenotypic extremes and pinpoint underlying candidate loci. Behavioral analysis and genetic manipulation indicates that this variation arises from genetic differences in the neuromodulatory architecture of the egg-laying circuitry. We provide experimental evidence that while strong egg retention can decrease maternal fitness due to in utero hatching, it may enhance offspring protection and confer a competitive advantage. Therefore, natural variation in C. elegans egg-laying behaviour can alter an apparent trade-off between different fitness components across generations. Our findings highlight underappreciated diversity in C. elegans egg-laying behavior and shed light on its fitness consequences. This behavioral variation offers a promising model to elucidate the molecular changes in a simple neural circuit underlying evolutionary shifts between alternative egg-laying modes in invertebrates.

Habitat selection of Culicoides spp. (Diptera: Ceratopogonidae) is influenced by the physicochemical factors such as temperature, pH, salinity, moisture, conductivity, organic and inorganic compounds of substrates. These factors determine the life history traits of the vectors. We studied the influence of substrate salinity (0–40 parts per thousand, ppt) and pH (pH 1–13) on oviposition, egg hatching, larval survivability, and adult emergence of Culicoides peregrinus Kieffer under laboratory conditions. Most eggs (80.74%) were laid in 0 ppt and 95% in pH 7 but lowered with increased salinity and pH levels. It was observed that the females did not lay eggs in 30 ppt to 40 ppt salinity; pH 1 and pH 13 but interestingly up to 95% of the eggs were retained within the abdomen. Little effect of salinity and pH on egg hatching was observed up to 5 ppt and 10 ppt except at the extreme values of 40 ppt and pH 1, pH 13. Pupation did not occur in rearing plates with high salinities, 30 ppt and 40 ppt, although the few eggs hatched when exposed to such salinity. In low salinity (0 to 2 ppt), occurrence of adult emergence was more and then decreased with increasing salinity. Maximum emergence was seen when the rearing media was alkaline. This study deals with the suitability of breeding substrate of C. peregrinus when exposed to salinity and pH ranges. Our study suggests the ambient salinity and pH ranges to be maintained during laboratory rearing of this vector species.

Ocean and freshwater conditions can influence spawning success of Pacific salmon (Oncorhynchus spp.) by governing the energy content of fish at the start of and during the spawning migration. Ocean conditions determine the energy stores of fish at the freshwater entry, while freshwater conditions determine how quickly stored energy is depleted as individuals migrate to spawning grounds in natal rivers and lakes. We assessed the occurrence of sockeye salmon (Oncorhynchus nerka) egg retention (failure to deposit eggs) in a high-latitude (~ 65°N) watershed that has a large, inter-annual variation in the number of returning adults. We also explored relationships between ocean and freshwater conditions with egg retention of female sockeye salmon. The proportion of females with egg retention (> 50 eggs) varied by threefold (12 to 36%) across years (2013 to 2020) and was related to ocean conditions represented by the North Pacific Index (NPI). Egg retention was more common in years with low NPI values (a stronger Aleutian Low) in association with the Pacific marine heatwave of 2014–2016 that disrupted food webs. This initial study contains the first empirical data observing the influence of ocean conditions on egg retention for any Pacific salmon population. The lack of any relationship between egg retention and freshwater temperatures was consistent with water temperatures primarily occurring below thresholds associated with heat stress related mortality (< 18 °C). Understanding the amount of egg retention and how environmental drivers influence egg retention within Pacific salmon populations provides insights for managers assessing the number of successful spawners and helps refine escapement-based management efforts.

Oviparous, facultative egg retention enables Drosophila females to withhold fertilized eggs in their reproductive tracts until circumstances favor oviposition. The propensity to retain fertilized eggs varies greatly between species, and is correlated with other reproductive traits, such as egg size and ovariole number. While previous studies have described the phenomenon, no study to date has characterized within-species variation or the genetic basis of the trait. Here, we develop a novel microscopebased method for measuring egg retention in Drosophila females and determine the range of phenotypic variation in mated female egg retention in a subset of 91 Drosophila Genetic Reference Panel (DGRP) lines. We inferred the genetic basis of egg retention using a genome-wide association study (GWAS). Further, the scoring of more than 95,000 stained, staged eggs enabled estimates of fertilization success for each line. We found evidence that ovary-and spermathecae-related genes as well as genes affecting olfactory behavior, male mating behavior, male-female attraction and sperm motility may play a crucial role in postmating physiology. Based on our findings we also propose potential evolutionary routes toward obligate viviparity. In particular, we propose that the loss of fecundity incurred by viviparity could be offset by benefits arising from enhanced mate discrimination, resource specialization, or modified egg morphology.

Background In arboviral disease systems where the virus can be transmitted from male to female vectors and from one generation to the next, targeting the female (especially when she is gravid) can help alter the persistence of the virus in nature and its transmission. A typical example is  Aedes   aegypti , which has become unmanageable due to the development of insecticide resistance. Despite evidence that monomolecular surface films prevent the selection of genetic resistance, their potential in  Aedes  vector control remains largely unexplored. Methods We examined the oviposition, egg retention, oocyte melanization, and female mortality of the Cayman Islands strain of  Ae. aegypti , using choice (balanced and unbalanced) and no-choice bioassays involving Aquatain® Mosquito Formulation (AMF; Aquatain Products Pty Ltd.), a polydimethylsiloxane–based liquid used for mosquito control. Results When presented with similar opportunities to oviposit in two sites treated with AMF and two other sites with untreated water (control), egg deposition rates were significantly higher in the untreated water sites than in the AMF-treated sites ( P  < 0.05). We also observed a matching pattern of egg deposition preference in environments with more options in terms of AMF-treated sites. Females laid significantly more eggs when water was the only available medium than when all sites were treated with AMF ( P  < 0.05). Also, significantly more mature eggs were withheld in the AMF no-choice environment than in the no-choice test involving only water ( P  < 0.05). Internal oocyte melanization was not observed in females from the oviposition arenas with the lowest AMF presence (equal-choice and water-based no-choice); in contrast, this physiological response intensified as the number of AMF-treated sites increased. Female death occurred at high rates in AMF-treated environments, and this response increased with the increasing presence of such egg deposition sites. Conclusions This study demonstrated that AMF acted as a deterrent signal to ovipositing  Ae. aegypti  and as an indirect adulticide. These results suggest that AMF may be a promising control tool against the dengue vector, and this warrants further evaluation under field settings. Graphical Abstract

Fundamental characteristics of the reproductive biology of female sand tiger sharks Carcharias taurus are needed to understand the periodicity, seasonality and environmental factors essential for reproduction in this iconic species. Animals in managed care, such as aquariums, provide the unique opportunity for longitudinal study in contrast to in situ sharks that are examined opportunistically, and at a single point in time. Additionally, comparison of reproductive observations from successfully reproducing in situ sharks and aquarium sharks may help elucidate reasons for lack of reproduction among aquarium sharks and aid the development of assisted reproductive techniques for managed populations. Reproductive status of in situ and aquarium female sharks was assessed using ultrasonography and plasma hormone (17 β -estradiol, testosterone, and progesterone) monitoring. The reproductive cycle was divided into eight stages based on ovarian activity and uterine contents. In situ sharks were sampled from Delaware Bay ( n = 29), North Carolina ( n = 39) and South Carolina ( n = 11) during April-November from 2015–2020. Nineteen aquarium females from five aquaria were examined longitudinally for two or more consecutive years. Reproductive regionalization was observed among in situ females with the majority (83%) of North Carolina females in an active state of reproduction and all Delaware females in a resting reproductive state. All aquarium females had a pattern of reproductive cycling that was consistent with alternating years of activity and rest with confirmed biennial ( n = 7) or triennial ( n = 3) reproductive cycles with spring seasonality. In contrast to in situ females, aquarium females often retained uterine eggs for 9-20 months after ovulation in the absence of a developing embryo(s). Pre-ovulatory aquarium females had significantly higher concentrations of 17 β -estradiol, testosterone and progesterone than other reproductive stages. For females in the ovulatory stage, in situ females had higher testosterone than aquarium females. Endocrine differences between successfully reproducing in situ females and aquarium females likely contribute to the limited reproductive success observed for this species in managed care and may be a reflection of diminished seasonal cues and environmental differences.

To support life, the osmolality of the cellular fluid is tightly regulated by various means, including osmolyte control. Dicarbonyl/L-xylulose reductase (DCXR) is a highly conserved enzyme reducing L-xylulose to xylitol, which serves as an effective osmolyte in various mammalian and human tissues such as lung epithelium, sperm, and lens. DHS-21 is the only DCXR ortholog in Caenorhabditis elegans, and DCXR null mutant worms accumulate eggs in the uterus. However, it has been unknown how and why the mutant worms impair egg retention. In this study, we tested whether the egg-retention in dhs-21 (jh129), the DCXR null mutant worm, is sensitive to changes in osmolarity. Low osmolality reverted the egg retention phenotype of dhs-21(jh129), while high osmolarity aggravated it. Also, knock-down of either one of osr-1, osm-7, or osm-11, osmoregulatory genes, also rescued egg-retention phenotypes of the null mutants. The study indicates that DCXR functions in fluid homeostasis by regulating cellular osmolality in C. elegans and provides insights into DCXR-involved clinical conditions, such as congenital cataracts and malfunctioning lung and kidney.

Background The sterile insect technique (SIT) aims at suppressing or decreasing insect pest populations by introducing sterile insects into wild populations. SIT requires the mass-production of insects and their sterilization through, for example, radiation. However, both mass-rearing and radiation can affect the life history traits of insects making them less competitive than their wild counterparts. In the malaria mosquito Anopheles arabiensis , some progress has been made to improve the mating competitiveness of mass-reared irradiated males. However, to date, no study has explored the relative effects of colonization and irradiation on important reproductive traits in this species. Such data may help to focus research efforts more precisely to improve current techniques. Methods Two strains of An. arabiensis originating from the same locality were used: one reared in the laboratory for five generations and the second collected as late larval instars in the field prior to experimentation. Pupae were irradiated with 95 Gy and some adult reproductive traits, including insemination rate, fecundity, oviposition behavior, fertility and male survivorship, were assessed in different mating combinations. Results Our study revealed the different effects of mosquito strain and irradiation on reproductive processes. The insemination rate was higher in field (67.3%) than in laboratory (54.9%) females and was negatively affected by both female and male irradiation (un-irradiated vs irradiated: 70.2 vs 51.3% in females; 67.7 vs 53.7% in males). Irradiated females did not produce eggs and egg prevalence was lower in the field strain (75.4%) than in the laboratory strain (83.9%). The hatching rate was higher in the field strain (88.7%) than in the laboratory strain (70.6%) as well as in un-irradiated mosquitoes (96.5%) than in irradiated ones (49%). Larval viability was higher in the field strain (96.2%) than in the laboratory strain (78.5%) and in un-irradiated mosquitoes (97.6%) than irradiated ones (52%). Finally, field males lived longer than laboratory males (25.1 vs 20.5 days, respectively). Conclusions Our results revealed that both irradiation and colonization alter reproductive traits. However, different developmental stages are not equally affected. It is necessary to consider as many fitness traits as possible to evaluate the efficacy of the sterile insect technique.

The phenology of egg production and oviposition in organisms affects survival and development of neonates and thus, both offspring and maternal fitness. In addition, in organisms with environmental sex determination, clutch phenology can affect hatchling sex ratios with attendant effects on population demography. The rapid rate of contemporary climate change might disrupt reproductive phenologies that evolved to match environmental conditions. To better understand the response of clutch phenology to annual and long-term changes in climate, we studied a population of Sonoran Desert Tortoises (Gopherus morafkai) in Arizona in 1993 and 1997–2005, specifically quantifying three phenophases, including (1) the estimated time of appearance of shelled eggs in females, (2) the estimated time that eggs were last visible in X-radiographs, and (3) the duration of the interval between the first two events. The mean date for appearance of shelled eggs was 6 June, and the mean date they were last visible was 26 June. After controlling for individual female effects, these dates were different among years. The total number of days that eggs were visible across all females within a year differed among years, but the mean duration of time that clutches were visible, after controlling for individual female effects, was similar among years. Three of 18 females exhibited interannual egg retention on 5 occasions from 52 clutches. Although G. morafkai ovulates only one clutch per year, they might oviposit up to two because of interannual egg retention. Most females produced shelled eggs through heat-unit accumulation achieving 8.3 degree days within a 14-d moving average. The ability to vary the timing of egg formation and oviposition might buffer G. morafkai from some of the effects of predicted increases in temperatures, but species-specific information on developmental temperatures and nesting behavior are needed to determine whether or not the species will be able to produce viable clutches of mixed sex ratios in a warmer climate.