The community ecology of Aedes egg hatching: implications for a mosquito invasion

Abstract. 1. A recently introduced treehole mosquito from Asia, Aedes albopictus , is spreading throughout eastern North America, especially in tyre-refuse piles. Previous studies have identified inhibitory effects of larvae on egg hatch as a potential population regulatory mechanism within Aedes. Larva-egg interactions may also occur between species. This experiment assesses the ability of larvae of A. albopictus and two possible competitors in North America, A.triseriatus and A.aegypti , to suppress hatching of conspecific and congeneric eggs.
2. We exposed eggs of each species to varying combinations of larval species and density for 24h and assessed subsequent hatch rates. Aedes albopictus eggs exhibited the lowest level of inhibition when exposed to high larval densities; moreover, at the lowest larval density they imposed the most intense interspecific hatch inhibition.
3. Discretionary hatching in response to larval density may influence community composition by promoting the spread of A.albopictus , perhaps even leading to its dominance within North American Aedes communities.     

Stock and parental effects on embryonic and early larval development of winter flounder Pseudopleuronectes americanus (Walbaum)

A hierarchical breeding design was used to determine if winter flounder Pseudopleuronectes americanus embryos and yolk-sac larvae sired by Georges Bank males developed and grew larger than fish sired by Passamaquoddy Bay males, and to examine parental contributions to variations in fertilization success, time to 50% hatch, hatch success and larval morphological development. Significant stock effects were detected for time to hatch and larval development. Eggs fertilized by Passamaquoddy Bay males reached 50% hatch significantly earlier than eggs fertilized by Georges Bank males. Larvae sired by Georges Bank males were significantly larger during larval development for four of the six traits measured at 12 days post-hatch: head depth, jaw length, myotome height and body area. Embryo and larval development were strongly influenced by maternal contributions; there were significant maternal variance components for the majority of the variables measured. Paternal variance components were significant for fertilization success, time to hatch, larval jaw length and larval head depth, however, they acted principally through parental interactions. This information has important implications for the long-term sustainable development of winter flounder for aquaculture purposes as well as for understanding winter flounder genetic variation in the wild.     

To hatch or not to hatch? Egg hatch response to larval density and to larval contact in a treehole mosquito

Abstract.

• 1 We investigated the effect on egg hatch of exposure to: (1) varying larval density, and (2) larval contact in Aedes triseriatus Say (Diptera: Culicidae). For 2 days in the laboratory we submerged eggs into a treehole water medium containing 0 (control), 4, 12 or 24 larvae that could either contact the eggs directly or were separated from them by a screen. Following treatment, abundance of microorganisms on the egg surfaces, a food source for newly hatched larvae and a proposed hatching stimulus, was assessed by counts made from serial dilutions of samples.
• 2 We discovered a complex hatching response to larval contact and to larval density, and an interaction between these two factors in their effect on microbial growth. Hatching was inhibited in the 0-larva control, even though microorganisms grew abundantly on the eggs. Hatch rate, as well as microbial counts, were high for eggs in direct contact with 4 larvae. As density increased in the larval contact treatment, microorganisms disappeared from the egg surfaces and hatch rate declined.
• 3 When protected from larval grazing, eggs supported numerous microbial colonies irrespective of larval density. In contrast to the contact treatment group, egg hatch increased with increasing larval density. These observations suggest that the combination of microbial growth and a larval factor stimulates hatch. This hatching response may have evolved because both abundant microorganisms and numerous larvae reflect a habitat of good quality.

     

Field evaluation of anthelmintic drug sensitivity using in vitro egg hatch and larval motility assays with Necator americanus recovered from human clinical isolates

A field-applicable assay for testing anthelmintic sensitivity is required to monitor for anthelmintic resistance. We undertook a study to evaluate the ability of three in vitro assay systems to define drug sensitivity of clinical isolates of the human hookworm parasite Necator americanus recovered from children resident in a village in Madang Province, Papua New Guinea. The assays entailed observation of drug effects on egg hatch (EHA), larval development (LDA), and motility of infective stage larvae (LMA). The egg hatch assay proved the best method for assessing the response to benzimidazole anthelmintics, while the larval motility assay was suitable for assessing the response to ivermectin. The performance of the larval development assay was unsatisfactory on account of interference caused by contaminating bacteria. A simple protocol was developed whereby stool samples were subdivided and used for immediate egg recovery, as well as for faecal culture, in order to provide eggs and infective larvae, respectively, for use in the egg hatch assay and larval motility assay systems. While the assays proved effective in quantifying drug sensitivity in larvae of the drug-susceptible hookworms examined in this study, their ability to indicate drug resistance in larval or adult hookworms remains to be determined.     

Biosteres longicaudatus: Developmental dependence on host (Anastrepha suspensa) physiology

Larvae of Anastrepha suspensa that were in the first day of the third instar were parasitized by females of the solitary endoparasitoid, Biosteres longicaudatus. At the end of the 6-hr oviposition period, larvae were ligated posterior to the ring gland so that some larvae had parasitoids anterior to the ligature while in others, the parasitoids were in the abdomen, posterior to the ligature. Ninety-two percent of the parasitoids anterior to the ligature hatched to the first through third instars. Parasitoids posterior to the ligature had a 75% egg hatch to the first instar only. No larval molts to the second or subsequent instars occurred in these parasitoids. Upon parabiosis to 3-day-old, unparasitized host pupae, the ligated larvae pupated and 97% of the first-instar parasitoids in these parabiosed larval abdomens molted to the second instar. Newly laid parasitoid eggs transplanted to 3-day-old pupal hosts had less than one-third of the egg hatch of those transplanted to first-day third-instar hosts. The data implicate the physiological state of the host (vis-a-vis pupation and associated events) as being an important factor in the development of the endoparasitoid.     

The influence of temperature on the stage at hatch of laboratory reared Gadus morhua and implications for comparisons of length and morphology

A staging table for yolk‐sac larvae of Atlantic cod Gadus morhua was developed and applied to determine the development stage at hatch. Larvae ( n  = 20) were sampled during the period from 50% hatch to first‐feeding from four temperature treatments ( c . 2, 4, 8 and 12° C). Data recorded included standard length, development stage, yolk‐sac area and evidence of feeding by larvae. The results indicated that the stage of development at hatch was positively correlated to larval size. Furthermore, developmentally based changes in morphology shortly after hatch reduced much of the initial difference in size, although some difference still existed. No relationship between size at hatch and the incidence of first‐feeding larvae was found. Based on these observations, it is recommended that the development stage of hatching larvae be reported in studies investigating size and morphological differences when observing individual larval fish that originate from different populations, batches or species.     

The ontogeny of chemically mediated antipredator responses of fathead minnows Pimephales promelas

The antipredator responses of adult and larval fathead minnows Pimephales promelas to chemical alarm cues prepared throughout ontogeny were tested using various behavioural assays. Larval epidermis was also examined during ontogeny using standard haematoxylin and eosin staining techniques. Adults elicited an antipredator response to chemical alarm cue made from larvae as young as 8–17 days post‐hatch. Interestingly, larvae did not possess visible club cells until 28–37 days post‐hatch and did not respond to conspecific chemical alarm cue until 48–57 days post‐hatch. These results suggest that chemical alarm cue may not be contained within club cells and that the components of larval and adult chemical alarm cue may be similar throughout ontogeny.     

Late‐life and intergenerational effects of larval exposure to microbial competitors in the burying beetle Nicrophorus vespilloides

Intergenerational effects can have either adaptive or nonadaptive impacts on offspring performance. Such effects are likely to be of ecological and evolutionary importance in animals with extended parental care, such as birds, mammals and some insects. Here, we studied the effects of exposure to microbial competition during early development on subsequent reproductive success in the burying beetle Nicrophorus vespilloides, an insect with elaborate parental care. We found that exposure to high levels of microbial competition both during a female's larval development and during her subsequent reproduction resulted in females rearing smaller broods than those exposed to lower levels of microbial competition. To determine whether these differences arose before or after offspring hatching, a cross‐fostering experiment was conducted. Our results demonstrate that the impact of larval competition with microbes for resources extends into adult life and can negatively affect subsequent generations via impacts on the quality of parental care provided after hatching. However, we also find evidence for some positive effects of previous microbial exposure on prehatch investment, suggesting that the long‐term results of competition with microbes may include altering the balance of parental investment between prehatch and post‐hatch care.     

Effects of some plant extracts on larval hatch of the root-knot nematode,Meloidogyne incognita

Abstract

The inhibitory effect of water extract of seed, leaf and bark of five plants, viz., Tamarindus indica, Cassia siamea, Isoberlinia doka, Dolnix regia and Cassia sieberiana was evaluated on larval hatch of Meloidogyne incognita in the laboratory. All the plant parts inhibited larval hatch of M. incoginta Percentage inhibition was higher in the seeds followed by the leaves and bark. Degree of inhibition observed, was directly related to the concentration of the extract. The standard suspensions inhibited hatching by about 97% while dilutions of S/100 inhibited larval hatch by 3%. Nematicidal activity of the plant parts of the five plants showed that C. siamea was the most effective followed by C. sieberiana, I. doka, T. indica and D. regia.     

Wheat germ oil and its effects on a liquid larval rearing diet for oriental fruit flies (Diptera: Tephritidae)

Wheat germ oil was added to a larval liquid diet for rearing Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) to optimize fruit fly quality. Effects of various concentrations of wheat germ oil at 0.04, 0.07, 0.15, 0.30, and 0.66% and their possible mode of action were evaluated. Results suggest that addition of wheat germ oil does not affect pupal weight, larval developmental period, adult emergence, mating ability, or peak time for egg production. But there was a significant increase in pupal recovery, percentage of adult fliers, egg production, or egg hatch for larvae fed the diet with wheat germ oil compared with those reared on the liquid diet without wheat germ oil. The increase in egg hatch and fliers was dose dependent. Therefore, addition of wheat germ oil to fruit fly rearing diet is a novel way to improve fruit fly quality, especially in egg hatch, fliers, egg production, and pupal recovery.     

The effect of time from hatch on the yolk conversion efficiency of rainbow trout, Salmo gairdneri

The growth and development of rainbow trout, Salmo gairdneri , from hatch to first feeding depends upon the nutrients stored in the yolk sac. The efficiency ( E ) with which yolk can be converted to larval biomass is a useful measurement in chronic toxicity tests, and it can be simply estimated by comparing the gain in larval weight ( L ) to the loss in yolk weight ( Y ) at hatch (time 0) and at any time t after hatch: E =( L ₁− L ₀)/( Y ₀− Y ₁); E may be calculated on a wet or dry weight basis. Although the rates of weight change were constant for the first 15 days after hatch at 10.5° C, E was not. E increased from near 0 and approached a value of 2.1 on a wet weight basis or 0.70 on a dry weight basis after 5–8 days. The variability of E was also very high shortly after hatch, but declined and stabilized within 5–9 days. For toxicity testing, we recommend that E be measured 10–15 days post-hatch to ensure precision with a minimum bias due to dissection error.     

THE INFLUENCE OF SOIL MOISTURE ON THE EMERGENCE OF LARVAE FROM CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHMIDT

The significance of soil moisture in relation to aeration and larval emergence from cysts of Heterodera schachtii Schmidt is discussed. The rate of larval emergence increased as oxygen concentration increased. A comparison of the moisture characteristics of a mass of cysts and of sand of about the same particle size showed that water was removed from between both the cysts and the sand particles at 12–16 cm. of water-pressure deficiency. There was an indication that water was removed from between the eggs within the cysts at 100–135 cm - of water-pressure deficiency. The rate of larval emergence showed a gradual decline is suction was increased beyond 20 cm. of water-pressure deficiency, approaching zero at 175 cm. of water-pressure deficiency. Results suggest that egg hatch is not directly dependent on pressure deficiency and that the presence of free larvae within the cyst inhibits further egg hatch. A technique is described for measuring larval motility in sand. There is a decline in motility when most of the water has been removed from the sand pore-spaces. It is suggested that the relatively low rates of larval emergence at high-pressure deficiencies are due to inhibition of larval migration from the cyst by the surface forces of the water film.     

A REVIEW OF LARVAL DEVELOPMENT IN THE INTERTIDAL LIMPET GENUS SIPHONARIA (GASTROPODA: PULMONATA)

A compilation of distributional and life-history data relatingto mode of larval development is presented for 26 species ofSiphonana, a genus of intertidal pulmonates. Most species depositgelatinous benthic egg masses with two species releasing pelagicegg masses. Fifteen species hatch as planktonic-developing larvae,nine hatch as direct-developing juveniles, and in a furthertwo larvae hatch with both the swimming velar apparatus (associatedwith plank-tonic development) and a crawling foot (associatedwith direct development). Data on mode of larval developmentare interpreted with respect to some adaptive models. Despiteimportant exceptions, there is support for adaptive models basedupon egg capsule size (direct developers hatch from larger eggcapsules) and intertidal distribution (direct developers generallyoccur higher on the shore than planktonic developers). Worldwide,planktonic developers are more widespread than direct-developingspecies, and individual planktonic species have a greater meanlatitudinal range. The evidence for adaptive models relatinglatitudinal distribution to developmental mode is equivocal.There appears to be no clear relationship between body sizeand developmental mode in the genus, although the smallest specieshas direct development and the largest has planktonic development.In most siphonariid subgenera, developmental mode appears tobe constant, but two subgenera contain a mixture of developmentaltypes (Received 1 November 1993; accepted 15 April 1994)     

Proteases released by Lucilia cuprina during egg hatch

Products released by Luclia cuprina (sheep blowfly) during egg hatch and early larval development were found to contain a variable number of proteases, probably reflecting their different functions during these developmental phases. Moreover, a number of the developmentally regulated proteases produced only during egg hatch appeared to be strongly egg shell associated, indicating the egg shell proteins to be their specific substrates. Several proteases were tested for their ability to enhance the rate of egg hatch. The commercial proteases chymotrypsin and trypsin were able to significantly enhance (p≤0.01) egg hatch by 36% and 44%, respectively, when compared to an untreated control. Interestingly, fluids containing the egg shell associated proteases were able to significantly (p≤0.001) enhance L. cuprina egg hatch by up to 70%. This hatch enhancement activity could be significantly (p≤0.001) reversed by the addition of Phenylmethylsulphonyl fluoride (PMSF). Fractionation of the egg-associated proteases by gelatin affinity chromatography suggested that gelatin-binding molecules were responsible for the majority of the egg hatch enhancement activity in this preparation.     

Embryogenesis and early larval development in wild-caught Levantine scraper,Capoeta damascina (Valenciennes, 1842)

Levantine scraper, Capoeta damascina is a candidate species for future stock assessments, conservation studies, and hatchery efforts. Herein, we documented embryonic and early larval development, from egg activation to the exogenous feeding period, using morphological and histological landmarks. Embryos were obtained by in vitro fertilization from hormonally induced wild-caught broodstock, and subsequent development was monitored at temperatures coinciding with native conditions. Embryonic development from fertilization to hatch lasted ~105–110 hr. Larvae emerged with unpigmented eyes and body morphology, as well as an undifferentiated digestive tract. The mouth was closed at hatch by the oropharyngeal membrane and opened by the early endogenous feeding period. Trabeculae cartilage, quadrate bone, and Meckel's cartilage of the endoskeleton were present during the endogenous feeding period. During this period, the larvae underwent considerable changes in craniofacial morphology, locomotion, and organogenesis of the digestive tract. The cartilaginous floor of the neurocranium developed and the first four ceratobranchials appeared simultaneously at the end of endogenous feeding period. The digestive tract was differentiated into buccopharynx, esophagus, and small intestine during the endogenous feeding period. The intestinal valve and numerous longitudinal folds at the posterior region of the intestine formed together by the endo–exogenous feeding period. Major developmental events in retinogenesis occurred during the endogenous feeding period. When larvae entered exogenous feeding the mouth was fully-functional. Additionally, liver size and eye diameter increased. Our analysis of embryonic and early larval development in Levantine scraper aligned with other freshwater fishes.     

Effects of temperature during early life history on embryonic and larval development and growth in haddock

The effect of incubation temperature (2, 4, 6, 8 and 10° C) on haddock Melanogrammus aeglefinus development and growth during the embryonic period and in subsequent ontogeny in a common post‐hatch thermal environment (6° C) was investigated. Hatching times were inversely proportional to incubation temperature and ranged from 20·3 days at 2° C to 9·1 days at 10° C. Growth rates were directly proportional to incubation temperature during both the embryonic and larval periods. There was a significant decline in growth rates following hatch in all temperature groups. Compared to the endogenously feeding embryos, growth rates in the exogenous period declined by 4·4‐fold at 4° C to 3·9‐fold at 8° C, indicative of the demarcation between the endogenous and exogenous feeding periods. Yolk utilization varied from 17 days at 2° C to 6 days at 10° C and followed a three‐stage sigmoidal pattern with the initial lag period inversely proportional to incubation temperature. Time to 50% yolk depletion varied inversely with temperature but occurred 1–1·5 days post‐hatch at all temperatures. Additionally, the period between 10 and 90% yolk depletion also decreased with increased temperature. Overall developmental rate was sequential with and directly proportional (2·3‐fold increase) to incubation temperature while the time spent in each developmental stage was inversely proportional to temperature. Larger embryos tended to be produced at lower temperatures but this pattern reversed following hatch, as larvae from higher temperature groups grew more rapidly than those from other temperature groups. Larvae from all temperatures achieved a similar length (c.total length 4·5 mm) upon complete yolk absorption. The study demonstrated the significant impact that temperature has upon developmental and growth rates in both endogenous and exogenous feeding periods. It also illustrated that temperature changes during embryogenesis had significant and persistent effects on growth in subsequent ontogeny.     

Residual effects of imidacloprid on Japanese beetle (Coleoptera: Scarabaeidae) oviposition, egg hatch, and larval viability in turfgrass

Preventive control of turf-infesting scarabaeid grubs by neonicotinoid insecticides is presumed to mainly result from residues killing first instars in the soil. The extent to which sublethal behavioral effects or intoxication of other life stages contribute to such control is poorly known. We tested whether Japanese beetle, Popillia japonica Newman, females lay fewer eggs in turf treated with imidacloprid (Merit 75 WP) or an imidacloprid-bifenthrin combination (Allectus GC SC), and whether exposure to those residues in thatch and soil reduces their survival and subsequent ability to feed or take flight. Effects of imidacloprid residues on egg hatch and viability of successive larval instars also were studied. In two sets of choice tests, 68 and 82% fewer eggs were laid in Kentucky bluegrass with Allectus residues than in controls. When females were confined in treated turf, however, neither insecticide consistently reduced their fecundity or affected depth at which eggs were laid, although exposure to fresh Allectus residues reduced the beetles' subsequent viability. Imidacloprid residues up to 2 ppm in soil did not affect egg viability or days to hatch, but they killed neonates soon after eclosion. Imidacloprid curatively applied at label rate (0.34 kg active ingredient/ha) reduced weight gain, burrowing capability, frass production, and survival of second and third instars in turfgrass cores, with high mortality within 30 d. Intoxication and behavioral impairment of third instars also occurred in autumn field trials. Our data suggest that imidacloprid has greater activity against late instars than is generally appreciated.     

Recruitment in Japanese sea bass,Lateolabrax japonicas (Cuvier, 1828): effects of timing on spawning and larval quality and quantity

This study aimed to elucidate the causes of variability in larval survival and juvenile abundance (recruitment) within and among cohorts of Japanese sea bass (JSB; Lateolabrax japonicus), a winter‐spawning temperate coastal marine fish. Larvae and settled individuals (settlers) belonging to four cohorts were collected from Tango Bay (the Sea of Japan coast) during eight sampling cruises in 2007 and 2008. Larvae were sampled in January and February each year using an ichthyoplankton net, and settlers were collected in February and March each year using a beam trawl. Age of individual larva and settlers was determined and growth history was back‐calculated from otolith microstructure, and the hatch date distribution was computed. Temperature, daily growth rate, size‐at‐age, hatch date, and density data of larvae and settlers allowed elucidating the effects of the timing of spawning and larval quantity and quality (growth rate and body size) on larval survival and recruitment within and among cohorts of JSB. Results showed that cohorts that hatched earlier in the season had higher quantity of larvae, experienced higher mean temperatures and survived better than cohorts hatched later. Recruitment variability among cohorts is determined largely by the initial quantity of larvae, as this explained >97% of the variability in recruitment among cohorts. Within cohorts, larger hatched larvae grew faster than their smaller conspecifics, and the bigger and faster growing larvae survived and settled. Results from this study suggest the following scenarios for recruitment of JSB: (i) earlier spawning in the season promotes larval survival since earlier cohorts are likely to encounter a better temperature and perhaps food conditions, and therefore recruit better than later cohorts; (ii) the initial quantity of larvae appears to be an important determinant of recruitment variability among cohorts; and (iii) the size‐ and growth‐related mechanisms operating during the larval phase appear to start at the time of the hatch.     

Synchronisation of egg hatching of brown hairstreak (Thecla betulae) and budburst of blackthorn (Prunus spinosa) in a warmer future

Synchronisation of the phenology of insect herbivores and their larval food plant is essential for the herbivores’ fitness. The monophagous brown hairstreak (Thecla betulae) lays its eggs during summer, hibernates as an egg, and hatches in April or May in the Netherlands. Its main larval food plant blackthorn (Prunus spinosa) flowers in early spring, just before the leaves appear. As soon as the Blackthorn opens its buds, and this varies with spring temperatures, food becomes available for the brown hairstreak. However, the suitability of the leaves as food for the young caterpillars is expected to decrease rapidly. Therefore, the timing of egg hatch is an important factor for larval growth. This study evaluates food availability for brown hairstreak at different temperatures. Egg hatch and budburst were monitored from 2004 to 2008 at different sites in the Netherlands. Results showed ample food availability at all monitored temperatures and sites but the degree of synchrony varied strongly with spring temperatures. To further study the effect of temperature on synchronisation, an experiment using normal temperatures of a reference year (T) and temperatures of T + 5°C was carried out in climate chambers. At T + 5°C, both budburst and egg hatch took place about 20 days earlier and thus, on average, elevated temperature did not affect synchrony. However, the total period of budburst was 11 days longer, whereas the period of egg hatching was 3 days shorter. The implications for larval growth by the brown hairstreak under a warmer climate are considered.     

Variance in rates of growth and development in larval and metamorphosing summer flounder, Paralichthys dentatus

Summer flounder, Paralichthys dentatus L., show variance in total length as they progress through larval development and metamorphosis, both in commercial aquaculture hatcheries and in research facilities. This variance leads to serious problems with cannibalism after settlement, if the fish are not ‘graded’ (i.e. separated by size), a labor‐intensive process. In order to document the magnitude of this variation and to try to understand the basis for it, we conducted a series of experiments during (a) the larval period and (b) the process of metamorphosis. The larval experiments were done on fish reared individually in small bowls and repeatedly measured during their development. The metamorphosis experiments were done on fish reared either communally or individually and repeatedly examined to determine the relationships between age, growth and stage of development. There was no relationship between size of larvae at 8 or 9 days after hatch (DAH) and their subsequent size at 30 DAH. During two larval trials, significant events occurred around 20–22 DAH: increased variability in size among offspring from one set of parents, and increased growth without increased variability among offspring from another set of parents. These findings suggest that selective breeding of this species might be a way of reducing size variability. During the metamorphosis trials, we found that rates of development and absolute growth in summer flounder are positively correlated.