Demographic study of two population outbreaks of Elasmoderus wagenknechti (Liebermann) (Orthoptera: Tristiridae) in the transitional desert of Chile

Under certain environmental conditions, several species of grasshoppers inhabiting rangeland areas (e.g., inter-valleys) of the Chilean transitional desert can irrupt demographically. One of them is Elasmoderus wagenknechti (Liebermann), an endemic species. We studied two outbreaks occurred in 1996 and 1999. The objectives of the research were to (i) estimate some demographic parameters associated with the aforementioned events, and (ii) compare between them the population parameters. The parameters we studied were density (ind/m(2)), sexual proportion, female fertility (i.e., eggs/female), and the relationship eggs/female versus female size. Density (ind/m(2)) ranged from 0.2 to 0.4 in 1996 and from 0.5 to 0.6 in 1999. ANOVA-tests registered differences in density among study sites and between years. In some of the study sites, females were more abundant than males (e.g., Lomas del Sauce). Females fertility ranged from 27 to 39 eggs per female, with significant differences among sites in 1996 but not in 1999. For females of 30-50 mm body size, a linear relationship was detected between egg number/female and body size. It is concluded that the E. wagenknechti outbreaks are site-specific in the study area and that the demographic parameters examined show a high variability among sites and between events.     

Reproductive variation and adult size in two co-occurring grasshopper species

ABSTRACT. 1. Egg sizes and clutch sizes of the grasshoppers Chorthippus brunneus (Thunb.) and Myrmeleotettix maculatus (Thunb.) were compared among three years and among three sites less than 1.3 km apart. Relationships between these reproductive traits and date of egg laying, body size and body condition were sought.
2. M.maculatus , the smaller species, laid fewer but larger eggs; and only the eggs of this species showed significant differences between sites and years.
3. A negative correlation between egg size and number per clutch was evident between species and years, but generally not among sites and among individuals of a population.
4. However, a hidden negative correlation between egg size and number was uncovered within populations when the relationship was examined for females of a given mature weight.
5. Variation in the number of eggs per clutch was explained statistically by a positive relationship between female body weight and egg number. Also, both interpopulation and intrapopulation comparisons revealed that for M.maculatus , but not for C.brunneus , females with long hind femurs laid large eggs.     

Two UV-sensitive targets in dorsoanterior specification of frog embryos

Previous work has shown that ultraviolet (UV) irradiation of fertilized frog eggs yields embryos that lack dorsal and anterior structures. The eggs fail to undergo the cortical/cytoplasmic rotation that specifies dorsoventral polarity, and they lack an array of parallel microtubules associated with the rotation. These eggs can be rescued by tilting with respect to gravity, and normal dorsoanterior development occurs. We find here that UV irradiation of Xenopus prophase I oocytes or Rana metaphase I oocytes also causes the dorsoanterior deficient syndrome, but the UV target is different from that in fertilized eggs. Tilting eggs, irradiated as oocytes, with respect to gravity, does not rescue dorsoanterior development, although lithium treatment does. The UV dose required to produce dorsoanterior deficiency for Rana metaphase I oocytes is much less than that for fertilized eggs, and the oocytes can form the array of parallel microtubules and undergo the cortical/cytoplasmic rotation after fertilization. Despite these features of normal development, no dorsoanterior structures form. While the UV target in fertilized eggs is thought to be the parallel microtubules (Elinson & Rowning, 1988; Devl Biol. 128, 185-197), the UV target in the oocytes may be a dorsal determinant.     

Egg performance on an egg-carrying bug. Experiments in the field

Selection of oviposition sites has direct influence on female fitness. Differences in offspring survival among sites should favour females to select oviposition sites with the highest survival. Golden egg bug females ( Phyllomorpha laciniata; Coreidae, Heteroptera) use conspecifics as oviposition substrates. Most eggs are laid on the back of the bug but they can be found on all body parts. Females never carry their own eggs, and males commonly carry eggs received without copulation with the donor. We examined differences in egg survival relative to paternity to the egg, host sex and body size and attachment of an egg on a host's body in the field. We also studied which bugs received eggs. Egg loss was surprisingly common: 30–80% of recaptured individuals lost eggs during a six-day period. Unexpectedly, host's paternity to the eggs did not affect egg survival. Also, egg loss did not differ among hosts in respect to other parameters studied. Males received more eggs than females, but survival of the eggs was not better on a male's back than on a female's back. Since egg loss is common in the golden egg bug, we suggest that female oviposition strategy to lay eggs on conspecifics is not perfect. This is due to active behaviour of potential hosts (for example, rejected oviposition attempts) or lack of suitable oviposition substrates (conspecifics) in the field. Since eggs do not survive unless carried, females may be acting opportunistically, doing the best job possible by laying eggs on available conspecifics.     

Trichogramma pretiosum parasitism and dispersal capacity: a basis for developing biological control programs for soybean caterpillars

In order to succeed in biological control programs, not only is it crucial to understand the number of natural enemies to be released but also on how many sites per area this releasing must be performed. These variables might differ deeply among egg parasitoid species and crops worked. Therefore, these trials were carried out to evaluate the parasitism (%) in eggs of Anticarsia gemmatalis and Pseudoplusia includens after the release of different densities of the egg parasitoid Trichogramma pretiosum. Field dispersal was also studied, in order to determine appropriate recommendations for the release of this parasitoid in soybean fields. The regression analysis between parasitism (%) and densities of the parasitoid indicated a quadratic effect for both A. gemmatalis and P. includens. The maximum parasitism within 24 h after the release was reached with densities of 25.6 and 51.2 parasitoids per host egg, respectively, for the two pests. Parasitism of T. pretiosum in eggs of P. includens decreased linearly as the distance of the pest eggs from the parasitoid release sites increased. For P. includens, the mean radius of T. pretiosum action and the area of parasitoid dispersal in the soybean crop were 8.01 m and 85.18 m2, respectively. We conclude that for a successful biological control program of lepidopteran pests using T. pretiosum in soybean fields, a density of 25.6 parasitoids per host egg, divided into 117 sites per hectare, should be used.     

Horizontal and vertical dispersal of dengue vector mosquitoes, Aedes aegypti and Aedes albopictus, in Singapore

To study the dispersal of dengue vector mosquitoes in Singapore, females of Aedes aegypti (L.) and Aedes albopictus (Skuse) (Diptera: Culicidae) were fed blood containing rubidium (Rb), which was detectable in their eggs by means of Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS). Laboratory calibration of the Rb reading, for a range of egg numbers from Rb-fed females, indicated a reasonably linear relationship and an unequivocal distinction between results with zero and one marked egg. Rb-marked female Aedes mosquitoes aged 3-5 days were released in semi-rural and urbanized parts of Singapore, with an array of ovitraps extending to a radius of 320 m from the release point. Subsequently, Rb-marked Aedes eggs were detected throughout the array, with similar distributions on each of the 4 days after release. More Rb was detected nearer the release point. However, when correction was made for the greater areas of zones further from the release point (and therefore presumably existence of more alternative oviposition sites), there were no significant differences in the numbers of marked eggs per ovitrap in the zones nearer or further from the release points. It is concluded that females of both these Aedes (Stegomyia) species could disperse easily and quickly throughout areas of radius 320 m in search of oviposition sites. This contrasts with the general belief that Ae. aegypti seldom flies more than 50 m and that control operations can safely be based on such an assumption. Releases on level 12 of a 21-storey apartment block, with ovitraps on each storey, showed similar easy and rapid dispersal to the top and bottom of the block.     

Role of kin recognition in oviposition preference and cannibalism by the predatory mite <Emphasis Type="Italic">Gynaeseius liturivorus</Emphasis>

Animals often select oviposition sites to minimize the predation risk for eggs and juveniles, which are more vulnerable to predation than adults. When females produce eggs in clusters, the eggs and juveniles are likely to suffer from cannibalism. Although cannibalism among siblings is known to be lower than among non-siblings, there have been few investigations into the possibility that females select oviposition sites that reduce the risk of cannibalism for the offspring. To test this possibility, we examined oviposition preference by adult females of the predatory mite Gynaeseius liturivorus in response to the presence of her own eggs and to eggs of other females, offering plastic discs as oviposition substrates. Although females did not clearly show a preference for plastic discs on which they had oviposited, they avoided plastic discs on which other females had oviposited. When eggs of other females were artificially placed on clean plastic discs, adult female mites avoided these discs, suggesting that the eggs were used as cues for oviposition preference. Cannibalism among juvenile siblings was lower than among non-siblings. These observations show that adult females and juveniles of G. liturivorus discriminate kin relationships among conspecific individuals. Therefore, oviposition preference by adult female G. liturivorus may lead to the reduced risk of cannibalism among offspring.     

Interspecific variation in desiccation survival time of Aedes (Stegomyia) mosquito eggs is correlated with habitat and egg size

Summary Survival times of eggs under three humidity conditions (42%, 68%, 88% RH) were investigated among Aedes (Stegomyia) mosquitoes from temperate and tropical zones (5 species and 20 geographical strains). This subgenus tends to occupy small aquatic sites as larvae, where desiccation resistance of eggs is necessary during habitat drought. Interspecific comparison showed that the egg survival time was correlated with egg volume and dryness of source locality, and probably with habitat. Aedes aegypti is associated most with arid climate and human-disturbed habitats — its large eggs survived the longest periods at all humidities. Aedes albopictus ranges from tropics to temperate zones and inhabits both disturbed and forest habitats — its eggs were less desiccation-resistant than A. aegypti eggs. The survival times for forest species eggs (A. riversi, A. galloisi, A. flavopictus) were variable at high humidities but at the lowest humidity were consistently shorter than for eggs of A. aegypti and A. albopictus.     

Frog breeding pond selection in response to predators and conspecific cues

Predators are a major influence on the breeding site selection decisions of anurans. Many species actively avoid breeding in habitat with predators when given the choice between predator and predator‐free sites. However, certain factors such as site fidelity or conflicting cues may preclude avoidance behavior. We conducted two experiments examining how western chorus frogs, Pseudacris triseriata, respond to predators, western mosquitofish, Gambusia affinis, using an array of artificial ponds located at two field sites. In one experiment, we added G. affinis to half of our experimental ponds and monitored subsequent colonization by frogs. We found that frogs laid significantly fewer eggs in ponds with fish compared to fishless ponds. In another experiment, we introduced an additional cue to complicate the decision‐making process and monitored colonization of ponds in response to treatments of conspecific breeding cues only (eggs), predators (G. affinis) only, and conspecific cues and predators. We found no significant differences in number of eggs deposited among these three treatments. Based on these results, P. triseriata does not always exhibit complete avoidance of fish predators, and avoidance may vary based on factors such as site fidelity or dispersal costs. This study represents a step toward understanding how multiple biotic factors at a breeding pond may influence anuran site selection behavior in the field.     

Parasitization of beet leafhopper eggs, Circulifer tenellus, in California

Parasitoids attacking eggs of beet leafhopper, Circulifer tenellus (Baker) (Hemiptera: Cicadellidae), were surveyed at eight sites in southern and central California for 2 years. One site was an insecticide‐free sugar beet field, and the remaining sites were all uncultivated and supported weedy vegetation. At each site, host plants of beet leafhopper were collected and stored until parasitoids emerged from the leafhopper eggs in the vegetation. Vegetation samples included both naturally occurring host plants and sugar beet outplants that were first infested with beet leafhopper eggs in the laboratory and then placed in the field for 2 days. Parasitism generally was highest in summer and lowest in winter. Beet leafhopper eggs were parasitized by the mymarids (Hymenoptera: Mymaridae) Anagrus nigriventris Girault, Polynema eutettexi Girault, P. longipes (Ashmead), Polynema sp., Gonatocerus capitatus Gahan and two Gonatocerus spp. from the litoralis species group, and the trichogrammatids (Hymenoptera: Trichogrammatidae) Aphelinoidea zarehi Triapitsyn, Walker and Bayoun, A. turanica Trjapitzin, A. roja Triapitsyn, Walker and Bayoun, A. anatolica Nowicki and Paracentrobia sp. near P. subflava (Girault). The most dominant were A. nigriventris, A. zarehi and Paracentrobia sp. The intensity of parasitism varied greatly among the sites with peak levels ranging from 13% to 82%. Species composition also varied among sites, especially between the sugar beet field where A. nigriventris was by far the most dominant parasitoid and the uncultivated sites where A. zarehi and/or Paracentrobia sp. usually dominated. Within the uncultivated sites, parasitoid species composition also varied between the sugar beet outplants and the naturally occurring vegetation; A. nigriventris was much more common in the former than in the latter.     

Lectin-binding properties of hamster egg zona pellucida and plasma membrane during maturation and preimplantation development

The structure and organization of the zona pellucida and plasma membrane of the hamster egg at various stages of maturation and development were examined using lectin-mediated agglutination and the binding of fluorescent-labeled lectins. Ricinus communis I and Dolichos biflorus lectins specifically agglutinated the zona pellucida of both unfertilized and fertilized eggs, while wheat germ agglutinin (WGA) only agglutinated eggs which had been pretreated with protease. Six other lectins failed to agglutinate even eggs pretreated with protease. A comparison of the lectin-binding sites on the zona pellucida of eggs in various stages of maturation and development revealed that the intensity of binding and distribution of fluorescent-labeled lectins remain unchanged. Zona-free eggs were agglutinated by every lectin tested except those recognizing -fucose-like residues. Fertilized zona-free eggs were slightly more agglutinable by concanavalin A (ConA), Lens culinaris and WGA than unfertilized eggs. When the surfaces of zona-free eggs were examined with fluorescent ConA, Ricinus communis I and WGA, maximal binding was seen when eggs reached full maturity and binding decreased during the later stages of preimplantation development.     

Dynamics of Winter Survival of Eggs and Juveniles of Meloidogyne incognita and M. arenaria

Winter survival dynamics of Meloidogyne incognita and M. arenaria were studied at nine sites in Texas for 2 years. Population survival from October until April was variable among sites, ranging from 0.1% to 33%. A negative correlation (r = -0.86, P = 0.01) was observed between initial population, densities in October and survival percentage until the following April. Total population (eggs + J2) and population of eggs declined continuously during the survival period. Populations of juveniles (J2) increased initially, then declined. The total populations were 82% eggs in October; hatch of these eggs was believed responsible for the observed increase in the population density of J2. Viable eggs were recovered from the soil until March. Eggs are as important as J2 in winter survival of M. incognita and M. arenaria in Texas. Survival data were analyzed by a simple mathematical model.     

Trophic egg laying: hypotheses and tests

Trophic egg-laying – wherein mothers provide non-developing eggs for offspring to eat – has attracted much empirical attention to diverse taxa (e.g. amphibians, non-social and eusocial insects, fish, and marine gastropods). However, there has been been only a limited exchange of ideas among studies of different taxa. We advocate a unified approach to the study of trophic eggs within an evolutionary ecological framework. In this paper, we stress the importance of elucidating the adaptive function of trophic eggs through explicit hypothesis testing, and our primary objective is to outline key experiments that can test adaptive and functional hypotheses. Currently, some cases of hypothesized trophic eggs may simply represent offspring consumption of eggs that failed to develop for non-adaptive reasons (e.g. sperm limitation). Furthermore, in many trophic egg-laying species, it is unclear whether trophic eggs have evolved to provision offspring or to reduce cannibalism among offspring. With increased focus on theory and hypothesis testing, the study of trophic eggs can offer important insight into topics such as sibling rivalry, parent–offspring conflict, and parental care.     

Motility and centrosomal organization during sea urchin and mouse fertilization

Motility and the behavior and inheritance of centrosomes are investigated during mouse and sea urchin fertilization. Sperm incorporation in sea urchins requires microfilament activity in both sperm and eggs as tested with Latrunculin A, a novel inhibitor of microfilament assembly. In contrast the mouse spermhead is incorporated in the presence of microfilament inhibitors indicating an absence of microfilament activity at this stage. Pronuclear apposition is arrested by microfilament inhibitors in fertilized mouse oocytes. The migrations of the sperm and egg nuclei during sea urchin fertilization are dependent on microtubules organized into a radial monastral array, the sperm aster. Microtubule activity is also required during pronuclear apposition in the mouse egg, but they are organized by numerous egg cytoplasmic sites. By the use of an autoimmune antibody to centrosomal material, centrosomes are detected in sea urchin sperm but not in unfertilized eggs. The sea urchin centrosome expands and duplicates during first interphase and condenses to form the mitotic poles during division. Remarkably mouse sperm do not appear to have the centrosomal antigen and instead centrosomes are found in the unfertilized oocyte. These results indicate that both microfilaments and microtubules are required for the successful completion of fertilization in both sea urchins and mice, but at different stages. Furthermore they demonstrate that centrosomes are contributed by the sperm during sea urchin fertilization, but they might be maternally inherited in mammals.     

Reproductive success in male sunbleak, a recent invasive fish species in the U.K.

The spawning behaviour of male nest guarding sunbleak Leucaspius delineatus , a recent invasive species in southern England, was studied and quantified for the first time. In the absence of physical differences between territorial and non‐territorial males ( i.e . colour, size, etc .), the reproductive behaviour of territorial males was analysed and related to reproductive success. The results showed that females preferred high‐courting and highly aggressive males. The initial cue in female mate choice, however, was based on courtship, while aggression was the decisive behavioural trait in influencing mate choice, providing a direct signal of physical condition and 'paternal competence'. Some males picked nest sites which were subsequently preferred by other males taking over the nest of a previous male ('communal nest'), with the new territorial male adopting the eggs already present at the nest. It appears that either due to female preference for nests already containing eggs or lower rates of sired egg predation by dilution among unrelated eggs, sunbleak males have adopted the mating strategy of allopaternal care.     

Arrayed primer extension: solid-phase four-color DNA resequencing and mutation detection technology

The technology and application of arrayed primer extension (APEX) is presented. We describe an integrated system with DNA chip and template preparation, multiplex primer extension on the array, fluorescence imaging, and data analysis. The method is based upon an array of oligonucleotides, immobilized via the 5' end on a glass surface. A patient DNA is amplified by PCR, digested enzymatically, and annealed to the immobilized primers, which promote sites for template-dependent DNA polymerase extension reactions using four unique fluorescently labeled dideoxy nucleotides. A mutation is detected by a change in the color code of the primer sites. The technology was applied to the analysis of 10 common beta-thalassemia mutations. Nine patient DNA samples, each of which carries a different mutation, and four wild-type DNA samples were correctly identified. The signal-to-noise ratio of this technology is, on the average, 40:1, which enables the identification of heterozygous mutations with a high confidence level. The APEX method can be applied to any DNA target for efficient analysis of mutations and polymorphisms.     

Why is mimicry in cuckoo eggs sometimes so poor?

I propose that the existence of imperfect adaptations (e.g. egg mimicry) in brood parasites and their hosts (e.g. discrimination abilities) could reflect age-dependent territory and nest-site selection patterns of the host. Studies of various passerines indicate that (1) older breeders tend to occupy nest sites of higher quality than do young birds (ideal despotic distribution resulting from interference competition), (2) nest-site selection affects the risk of parasitism in various habitats, (3) egg recognition in passerines has a strong learning component (therefore naive breeders tend to accept whereas older birds tend to reject parasitic eggs). Because young naive birds, who tend to accept parasitic eggs, usually breed in low-quality areas where they are frequently parasitised, while old experienced birds, who tend to reject parasitic eggs, breed in high-quality areas where they are rarely parasitised, the distribution of acceptors and rejecters with respect to the risk of parasitism is non-random, i.e. populations of some host species may consist of heavily parasitised acceptors and weakly parasitised rejecters. Therefore, the selection pressure exerted by the host on the parasite should be weaker than if brood parasitism was randomly distributed among naive and experienced breeders and affect adaptations such as egg mimicry. This could explain the existence of imperfect adaptations in some brood parasite-host systems.     

Intraspecific competition as a selective pressure on the choice of oviposition site in a phytophagous insect

Our aim was to clarify the factors providing selective pressures on the choice of oviposition sites in phytophagous insects. To this end, we examined the spatial distribution of eggs of the sawfly leaf miner, Profenusa japonica . The study was conducted over five consecutive years on three subpopulations found in riverbeds in central Japan. Profenusa japonica lays eggs on leaflets of Rosa multiflora , and its larvae mine a single leaflet for the entire larval stage. The egg distribution among leaflets was uniform (regular) at all sites examined in each year. The distribution within leaflets was also uniform, and it appeared that females avoided ovipositing on areas of the leaf that already contained eggs. Few parasitoids were found in eggs or larval stages, despite intensive examination. Larval mortality increased, mainly as a result of exploitative competition, when there were two or three larvae per leaflet. Starvation caused by resource competition for leaflet tissues was an important mortality factor. Therefore, we suggest that P. japonica females avoided ovipositing on areas of the leaflet that already contained eggs to prevent exploitative competition among larvae sharing the same leaflet.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 641–650.     

High-throughput molecular identification of fish eggs using multiplex suspension bead arrays

The location and abundance of fish eggs provide information concerning the timing and location of spawning activities and can provide fishery-independent estimates of spawning biomass. However, the full value of egg and larval surveys is severely restricted because many species' eggs and larvae are morphologically similar, making species-level identification difficult. Recent efforts have shown that nearly all species of fish may be identified by mitochondrial DNA (mtDNA) sequences (e.g. via 'DNA barcoding'). By taking advantage of a DNA barcode database, we have developed oligonucleotide probes for 23 marine fish species that produce pelagic eggs commonly found in California waters. Probes were coupled to fluorescent microspheres to create a suspension bead array. Biotin-labelled primers were used to amplify the mitochondrial cytochrome oxidase subunit I (COI) and 16S ribosomal rRNA genes from individual fish eggs. The amplicons were then hybridized to the bead array, and after the addition of a reporter fluorophore, samples were analysed by flow cytometry with Luminex 100 instrumentation. Probes specifically targeted eggs that are abundant and/or from morphologically indistinguishable species pairs. Results showed that the 33 different probes designed for this study accurately identified all samples when PCR was successful. Suspension bead arrays have a number of benefits over other methods of molecular identification; these arrays permit high multiplexing, simple addition of new probes, high throughput and lower cost than DNA sequencing. The increasing availability of DNA barcode data for numerous fish faunas worldwide suggests that bead arrays could be developed and widely used for fish egg, larval and tissue identifications.     

The oviposition sites of five leafhopper species (Horn. Auchenorrhyncha) on Holcus mollis and H.lanatus

Abstract. 1. A study was made of the oviposition sites of five leafhopper species Diplocolenus abdominalis, Recilia coronifera, Errastunus ocellaris, Elymana sulphurella (Cicadellidae) and Dicranotropic hamata (Delphacidae) on the grasses Holcus mollis and H.lanatus.
2. Experiments were made in the laboratory, each insect species being provided simultaneously with a complete plant of both Holcus species.
3. Distribution of eggs within the leaf sheath and leaf blade, and their height above ground-level, were recorded.
4. The presence and size of egg groups were noted, as well as the angle of eggs to the longitudinal axis of the leaf.
5. On the basis of comparison of the vertical distribution of the eggs with availability of plant tissues, the five species can be divided into three groups: (a) D.abdominalis and R.coronifera , (b) D.hamata and E.ocellaris , (c) E.sulphurella. Species within a group, i.e. with similar distributions of eggs, have other features separating their oviposition sites.