Egg Patches Research Articles

Partial exploitation of host egg patches resulting from a high rejection rate of healthy hosts cautions the mechanistic use of functional response models

Abstract The functional response of parasitoids is a main component of models that describe host–parasitoid interactions. When the functional response assumed in a model (e.g., a population model) is inaccurate, predictions by the model based on the functional response also become unreliable. This study reports that conventional functional response models may commonly fail to capture the actual functional response of parasitoids and discuss its implications. To assist the discussion, an experiment was conducted to describe interactions between the pupal parasitoid Dirhinus giffardii (Hymenoptera: Chalcididae) and its host Bactrocera dorsalis (Diptera: Tephritidae) in the laboratory. Results showed that the parasitoids typically interacted with all hosts in the environment but parasitised a small fraction of them (e.g., most encountered hosts were rejected), which deviates from the assumption of mechanistic functional response models. An increasing number of published studies on functional response also suggest (although circumstantially) the rejection of unparasitised hosts is common, suggesting that this behaviour is widespread among parasitoid species. By using the experimental results, the study discusses why existing hypotheses are insufficient for the observed behaviour and the implications of this behaviour within the realm of theories surrounding host–parasitoid interactions.

Parasitism by Gryon aetherium (Hymenoptera: Scelionidae) on Bagrada hilaris (Hemiptera: Pentatomidae) eggs in northcentral California.

Bagrada bug, Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae), is an invasive pest of cruciferous crops. The parasitoid Gryon aetherium Talamas (Hymenoptera: Scelionidae) is a promising biological control agent for B. hilaris because it can forage in the soil where B. hilaris deposits most of its eggs. In this study, we assessed parasitism by G. aetherium on B. hilaris eggs in situ in northcentral California, including the Salinas Valley where most cruciferous crops in the United States are grown. Parasitism was documented by leaving soil-filled trays under infested plants for 7-14 days, then removing eggs and holding them for emergence of parasitoids. Gryon aetherium accounted for over 99% of emerged parasitoids, and occurred at 11 of the 12 sampled sites. Of the 17,729 and 31,759 B. hilaris eggs collected in 2021 and 2022, 1,518 (8.84%) and 2,654 (8.36%) were parasitized by G. aetherium, respectively. Parasitism rates were generally higher inland and ranged from 3.64% to 44.93% in 2021 and from 1.01% to 23.04% in 2022, and never exceeded 15% on any sample dates at several coastal sites in the Salinas Valley. Discovery efficiency (a measure of the ability of parasitoids to locate egg patches) reached 80% or higher at all but 1 site, but exploitation efficiency (a measure of the ability of parasitoids to exploit the egg patch after it has been discovered) was generally <20%, suggesting that G. aetherium can locate egg patches efficiently but is less efficient at finding eggs within patches.

Direct and Indirect Competitive Interactions between Ooencyrtus nezarae and Paratelenomus saccharalis Parasitizing Megacopta cribraria Egg Patches.

The present study investigated egg parasitoid interspecific interactions between a generalist, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and a specialist, Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) in a laboratory setting using kudzu bug (Megacopta cribraria Fabricius, (Hemiptera: Plataspidae)) eggs as their shared host. Three experiments were conducted to evaluate the emergence of wasps from parasitized hosts after the simultaneous and sequential release of wasps, monitor aggressive behavior of P. saccharalis, and quantify intraguild predation of O. nezarae larvae on heterospecific P. saccharalis larvae. Results showed that total host egg parasitism was higher when both wasps were released simultaneously than if wasps were released sequentially. Ooencyrtus nezarae produced more total offspring than P. saccharalis in all sequential/simultaneous treatments but produced male offspring in most cases. In the aggressive behavioral experiment, specialist, P. saccharalis used head butting to fight O. nezarae, but no other aggressions were observed. In an experiment examining intraguild predation, O. nezarae was able to develop in host eggs parasitized by P. saccharalis four days earlier, acting as a superior larval competitor. These findings shed light on the potential interspecific interactions between O. nezarae and P. saccharalis, which may determine their relative abundance and influence their compatibility in kudzu bug biological control programs.

Pengaruh sinar bulan terhadap telur Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) pada lahan bawang merah

Spodoptera exigua (Hübner) merupakan serangga nokturnal dan menjadi salah satu hama penting di pertanaman bawang merah. Aktifitas serangga nokturnal dipengaruhi oleh sinar bulan. Penelitian ini bertujuan untuk mengetahui pengaruh sinar bulan terhadap perilaku letakan telur, yaitu jumlah kelompok telur, jumlah telur per kelompok telur, dan pola distribusi kelompok telur S. exigua. Penelitian dilaksanakan pada tiga lahan bawang merah di Kabupaten Brebes, Jawa Tengah selama bulan baru, setengah, dan penuh. Pengambilan sampel meliputi pengamatan jumlah kelompok telur, jumlah telur per kelompok telur, dan pola distribusi kelompok telur S. exigua pada setiap plot pengamatan. Penentuan pola distribusi kelompok telur S. exigua berdasarkan indeks Morisita. Hasil penelitian menunjukkan bahwa jumlah kelompok telur dan jumlah telur per kelompok telur selalu meningkat dari bulan baru, setengah, dan penuh. Secara umum, pola distribusi kelompok telur S. exigua adalah mengelompok pada tiga kondisi sinar bulan. Intensitas sinar bulan yang tinggi (bulan penuh) dapat meningkatkan jumlah kelompok telur dan jumlah telur per kelompok telur S. exigua serta berpotensi menimbulkan serangan yang lebih parah.

Egg boons: central components of marine fatty acid food webs.

Food web relationships are traditionally defined in terms of the flow of key elements, such as carbon, nitrogen, and phosphorus, and their role in limiting production. There is growing recognition that availability of important biomolecules, such as fatty acids, may exert controls on secondary production that are not easily explained by traditional element-oriented models. Essential fatty acids (EFAs) are required by most organisms for proper physiological function but are manufactured almost entirely by primary producers. Therefore, the flow of EFAs, especially docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA), through aquatic food webs is critical for ecosystem functioning. A meta-analysis of data on the EFA content of marine organisms reveals that individual eggs of marine animals have exceptionally high concentrations of EFAs, and that superabundances of eggs released in temporally and spatially discrete patches create rich, but temporary, nutritional resources for egg predators, called "egg boons." Mortality rates of fish eggs are disproportionately higher than animals of similar size, and those eggs are consumed by predators, both larger and smaller than the adults that produce the eggs. Thus, egg boons are a major trophic pathway through which EFAs are repackaged and redistributed, and they are among the few pathways that run counter to the main direction of trophic flow. Egg boons can transport EFAs across ecosystems through advection of patches of eggs and spawning migrations of adults. Recognizing the significance of egg boons to aquatic food webs reveals linkages and feedbacks between organisms and environments that have important implications for understanding how food webs vary in time and space. Examples are given of top-down, bottom-up, and lateral control mechanisms that could significantly alter food webs through their effects on eggs. Our results suggest that trophodynamic food web models should include EFAs generally, and egg production and egg EFA content in particular.

Effectiveness of the egg parasitoid Trichogramma evanescens preventing rice moth from infesting stored bagged commodities

Experiments were carried out in the laboratory with the aim of accessing the effectiveness and parasitism by Trichogramma evanescens to prevent Corcyra cephalonica from infesting rice in paper and jute bags. Eight small jute or paper bags filled with 5 kg of organic rice grains were prepared and the openings sealed. Sentinel egg cards were prepared with thirty fresh eggs of C. cephalonica glued onto small pieces of paper cardboard. Eight sentinel egg cards were introduced into a plastic box measuring 60 × 40 × 21 cm, i.e four cards on top surface of the bag and the box bottom, respectively. Approximately 500 adults of T. evanescens were released 10–30 cm away from the egg cards. The control boxes contained no parasitoids; there were five replicates for all treatments and controls. Two experimental conditions were tested, i) placing a single T. evanescens-release unit with sentinel egg cards placed every 3–4 days without any further replacement of the release unit for three weeks, ii) both new host eggs and T. evanescens release units were replaced every 3–4 days. Mean emergence of C. cephalonica was significantly (p > 0.001) suppressed by the release of T. evanescens. There was statistically no significant difference on the number of emerged moths on paper bag compared to jute bag. All sentinel egg patches were visited by T. evanescens. There was no correlation between the distance (10–30 cm) at which the sentinel egg cards were placed away from the T. evanescens release point and the number of parasitized C. cephalonica eggs. There was no decrease in parasitism over time. The results demonstrate that T. evanescens has the potential for host-location ability and parasitism of C. cephalonica both on paper and jute bags. This parasitoid could be a promising candidate for the biological control of moth pests in bagged stored products.

The sublethal effects of deltamethrin on Trichogramma behaviors during the exploitation of host patches

Trichogramma and parasitoids as a whole are key species because they regulate natural populations of other insects. As any non-target species, this parasitoid can be exposed to insecticides by environmental pollution. This study identified the effects of an LD 20 of deltamethrin (a pyrethroid) on the behavior of Trichogramma brassicae females infesting a patch of host eggs. The study found that females that survived exposure to the insecticide infested fewer host eggs; spent more time on unsuitable, previously infested host eggs; and infested more previously infested host eggs than controls. The insecticide also induced an increase in antennal and ovipositor rejection of previously infested host eggs. These results are discussed in the light of the mode of action of pyrethroid insecticides. The findings of the study highlight sublethal effects that reduce the fitness of parasitoids and that could consequently modify the equilibrium of natural ecosystems.

Identification of marine fish egg predators using molecular probes

Mortality during the egg and larval stages is thought to play a major role in determining year-class strength of many marine fish. Predation of eggs and larvae is normally considered to be a major factor but the full suite of predators responsible has rarely been identified. Potential predators on a patch of plaice Pleuronectes platessa eggs located in the eastern Irish Sea were mapped using acoustics and sampled by trawl and a plankton multi-net. Gut contents of 3373 fish, crustacea and cephalopods sampled in the area were screened using a plaice-specific TaqMan DNA probe. Herring Clupea harengus and sprat Sprattus sprattus dominated trawl catches and showed high positive TaqMan responses (77 and 75% of individuals tested respectively). Locations of clupeid schools also broadly corresponded with the distribution of fish eggs in the plankton. Whiting Merlangius merlangus were also reasonably abundant in trawl hauls and 86% of their stomachs tested positive for plaice DNA. Species showing lower levels of positive TaqMan response included mackerel Scomber scombrus, poor cod Trisopterus minutus, squid Loligo spp., dogfish Scyliorhinus canicula and weever Trachinus vipera. Non-reactivity of all negative controls precluded the occurrence of cross-contamination, and positive reactions from demersal species, such as dogfish and weever, may have resulted from secondary predation. No benthic macro-crustaceans tested positive. Samples of planktonic organisms yielded 13% positive TaqMan reactions, mainly from clupeoid or sandeel (Ammodytidae) larvae, but also included some Malacostraca and Amphipoda. Use of the molecular approach allowed rapid screening of a large number of potential predators of plaice eggs, and the results provide a more holistic description of the predator community than has previously been achieved.

Quantity, Structure, and Habitat Selection of Natural Spawning Reefs by Walleyes in a North Temperate Lake: A Multiscale Analysis

AbstractSpawning habitat, the cornerstone of self‐sustaining, naturally reproducing walleye Sander vitreus populations, has received limited quantitative research. Our goal was to quantitatively describe the structure and quantity of natural walleye spawning habitat and evaluate potential selection of habitat in Big Crooked Lake, Wisconsin. In 2004 and 2005, we located and delineated walleye egg deposition polygons through visual snorkel and scuba surveys. We also delineated recently deposited, adhesive egg patches daily along one spawning reef in 2005. To determine habitat selection, we quantified and compared spawning and lakewide available habitat at different scales. In both years, walleyes used similar spawning habitat, including three geomorphic types: linear shorelines, a point bar, and an island. Walleyes used only 14% of the entire lake shoreline and 39% of the shoreline comprised of gravel (6.4–76.0 mm), cobble (76.1–149.9 mm), or coarser substrates for spawning in 2005, indicating selection of specific spawning habitat. Lakewide, walleyes spawned close to shore (outer egg deposition polygon boundary mean distance = 2.7 m), in shallow water (outer egg deposition polygon boundary mean depth = 0.3 m), and over gravel substrate (percent coverage mean = 64.3) having low embeddedness (mean = 1.30). Our best nearshore (0–13‐m) resource selection function predicted an increase in the relative probability of egg deposition with the increasing abundance of gravel, cobble, and rubble (150.0–303.9‐mm) substrates and a decrease with increasing distance from shore and water depth (89.9% overall correct classification). Adhesive egg patches confirmed that walleyes actively chose nearshore, shallow‐water, and coarse‐substrate spawning habitat. The quantitative habitat information and predictive models will assist biologists in developing walleye spawning reef protection strategies and potentially aid in designing and evaluating artificial spawning reefs.

An Unprecedented Aggregation of Whale Sharks, Rhincodon typus, in Mexican Coastal Waters of the Caribbean Sea

Whale sharks, Rhincodon typus, are often perceived as solitary behemoths that live and feed in the open ocean. To the contrary, evidence is accumulating that they are gregarious and form seasonal aggregations in some coastal waters. One such aggregation occurs annually north of Cabo Catoche, off Isla Holbox on the Yucatán Peninsula of Mexico. Here we report a second, much denser aggregation of whale sharks (dubbed “the Afuera”) that occurs east of the tip of the Yucatán Peninsula in the Caribbean Sea. The 2009 Afuera event comprised the largest aggregation of whale sharks ever reported, with up to 420 whale sharks observed in a single aerial survey, all gathered in an elliptical patch of ocean approximately 18 km2. Plankton studies indicated that the sharks were feeding on dense homogenous patches of fish eggs, which DNA barcoding analysis identified as belonging to little tunny, Euthynnus alletteratus. This contrasts with the annual Cabo Catoche aggregation nearby, where prey consists mostly of copepods and sergestid shrimp. Increased sightings at the Afuera coincide with decreased sightings at Cabo Catoche, and both groups have the same sex ratio, implying that the same animals are likely involved in both aggregations; tagging data support this idea. With two whale shark aggregation areas, high coastal productivity and a previously-unknown scombrid spawning ground, the northeastern Yucatán marine region is a critical habitat that deserves more concerted conservation efforts.

Old and new host-parasitoid associations: parasitism of the invasive fruit fly Bactrocera invadens (Diptera: Tephritidae) and five African fruit fly species by Fopius arisanus, an Asian opiine parasitoid

Fopius arisanus (Sonan), a solitary koinobiont endoparasitoid of fruit flies, was introduced for testing and final release against the recently discovered species Bactrocera invadens Drew, Tsuruta and White in Africa. Laboratory experiments were conducted to assess host preference, host acceptability for oviposition, and physiological suitability of B. invadens and five other indigenous tephritid fruit fly species, namely, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), C. cosyra (Walker), C. rosa Karsch, C. fasciventris (Bezzi), and C. anonae Graham. Females of F. arisanus visited all host egg patches, but showed a stronger preference to eggs of B. invadens, which was also most accepted for oviposition. Successful development of parasitoid progenies varied greatly across hosts, with B. invadens yielding the highest parasitoid progeny and C. fasciventris yielding no F. arisanus progeny. Most of the parasitoid eggs laid in C. rosa and C. fasciventris were encapsulated. Sex ratio was not influenced by host species and it was female biased in all hosts that produced parasitoid progeny. Fopius arisanus was able to establish a new association with C. capitata, C. cosyra and to a lesser extent C. anonae. The results are discussed in the light of the potential use of F. arisanus as a biological control agent of B. invadens.

Oviposition behavior and progeny production of Trichogramma evanescens (Hymenoptera: Trichogrammatidae) in patches of single and clustered host eggs

The oviposition behavior of T. evanescens in each patch type (1mm 2 ) with 12 single spaced or clustered eggs of Anagasta kuehniella Zeller was observed continuously, recorded and calculated the patterns of patch use, time budgets, and the sequence of sex allocation for up to 1 hr. or until the female le ft the patch. The only significant behavioral event is the total walking in cluster patch because the female takes significantly more time walking out of patch. The parasitoid spends much time resting on eggs of cluster patch than in single patch. No significant differences occurred between single and cluster patches in their influence on the residence time spent in a patch. The handling time in a patch showed significant differences between single and cluster patch. There is no giving up time in single patch but it happened in cluster patch. Clustered patches led to a reduction in percent drumming and grooming time, but an increase in percent resting and total walking time . There were no significant differences between single and cluster patches in the number of eggs encountered. The progeny sex ratio from the parasitized eggs showed very little variation and was insignificant between patch types. The per cent male progeny was 16.1 and 21.2 % in single and cluster patches, respectively. There were no significant differences for oviposition time for both male or female eggs in single and cluster patches. The female tended to produce male eggs at the second oviposition event in single patch which represented 16.67 % of the total male eggs deposited, while it deposited male eggs (8.7 %) at the first oviposition event. This study has important implications for Trichogramma inundation programs and selecting Trichogramma species and strains, it should be taken into consideration to match the behavioral and reproductive characteristics of Trichogramma species to the ovipositional strategies (single eggs versus egg masses) of target pests .

Predation and oviposition by predatory Stethorus japonicus, Oligota kashmirica benefica, and Scolothrips takahashii in egg patches of various spider mite species

AbstractPredation and oviposition by three predacious insects [Scolothrips takahashii Priesner (Thysanoptera: Thripidae), Stethorus japonicus H. Kamiya (Coleoptera: Coccinellidae), and Oligota kashmirica benefica Naomi (Coleoptera: Staphylinidae)] were examined using egg patches of three spider mite species [Amphitetranychus viennensis (Zacher), Tetranychus urticae Koch, and Panonychus mori Yokoyama (all Acari: Tetranychidae)] that are pest species on Japanese pear [Pyrus serotina Rehder (Rosaceae)]. Scolothrips takahashii females consumed more prey and laid more eggs in A. viennensis and T. urticae egg patches than in P. mori egg patches. Females also left P. mori egg patches sooner than they left other egg patches even at high prey density. Predation and oviposition of S. takahashii in a prey patch were greatly enhanced by the complicated webs produced by A. viennensis. Stethorus japonicus females consumed significantly more prey and laid more eggs in A. viennensis egg patches than in P. mori egg patches, with intermediate values in T. urticae egg patches, reflecting the quality of each spider mite species as prey. Oligota kashmirica benefica females consumed more prey and laid more eggs in A. viennensis and T. urticae egg patches than in P. mori egg patches, particularly at high prey density. However, predation and oviposition by O. kashmirica benefica increased greatly with increasing prey density, even in P. mori egg patches, indicating that prey density was the most important factor in predation and oviposition by this species. These results are discussed in relation to the potential effect of each predator on the suppression of different spider mite species on Japanese pear.

Spawning of the southern hake Merluccius australis (Pisces: Merlucciidae) in Chilean fjords

The southern hake Merluccius australis constitutes an important fishery in southern Chile, but its reproductive biology is scarcely known, and until now the Chilean fjords have not been considered as potential spawning zones. Oceanographic surveys carried out during austral spring and summer of 1995–2002 in the Chilean fjords (43°30′S–47°S), are used to describe for first time the spawning of M. australis in the inland sea of southern Chile. Large patches of eggs with undeveloped embryos (<4 days old, >150 eggs per 10 m 2), eggs in late development and abundant southern hake larvae (up to 385 larvae per 10 m 2) were observed inside Chilean fjords during austral spring season. Eggs and preflexion larvae (<9 mm) were scarcely detected in open ocean-influenced waters (<30 ind per 10 m 2). This pattern of horizontal distribution may be determined by spawning events of inland resident stocks and/or by inshore migration of adult hakes during austral spring. The higher frequency of small larvae inside fjord waters, and the presence of postflexion larvae outside fjords are indicative that fjords are used also as nursery areas for early stages of southern hake. Finally, inter-annual variability in egg size (i.e., diameter) was detected, despite the relatively constant seawater temperature (10–11 °C). Further investigations are needed to determine the maintenance and the health of this spawning and early nursery area in a zone highly disturbed by salmon culture activity.

Fine-scale distribution of sardine ( Sardina pilchardus) eggs and adults during a spawning event

High-resolution acoustic and ichtyoplankton sampling with a ‘continuous under-way fish egg sampler (CUFES)’ was performed in two regions of approximately 100 square nautical miles off southern Iberian Peninsula, with the aim of studying the small scale distribution of sardine ( Sardina pilchardus) adults and eggs during a spawning event. Very dense patches (246 eggs m − 3 ) of recently spawned eggs with dimensions (up to 3 nautical miles wide) significantly larger than daytime sardine schools were present in both regions. Egg staging and ageing showed very little intra-sample variation, indicating a synchronous spawning period at dusk. The internal structure of the patches evaluated by variography showed very low internal variability, as if they consisted of a single unit. This hypothesis is confirmed by the acoustic finding of large sardine shoals with similar dimensions to those of the patches after sunset and throughout the night. During that period, adults were found near or in contact with the bottom, suggesting that spawning occurred at depth. A distinct patch of older eggs was found in both areas, but with a few nautical miles of horizontal separation. Their characteristics (a larger area, lower egg densities and a more irregular shape) indicate that these patches were exposed to dispersion and ‘stirring’ by physical forces, reshaping their initial appearance, while mesoscale water circulation could have displaced the core of the patches away by several kilometres within a day.

Oviposition Sites of the Cypress Seed Bug Orsillus maculatus and Response of the Egg Parasitoid Telenomus gr. Floridanus

Phytophagous insects have many strategies to escape parasitoids, for example by hiding eggs into plant tissues, but oviposition in holes made by another insect is rather scarce. The cypress seed bug Orsillus maculatus Fieber (Heteroptera: Lygaeidae) is strictly dependent on the availability of cones of Cupressus sempervirens L. to oviposit. Females lay eggs either in exit holes cut through the cone scale by emerging adults of the cypress seed chalcid, Megastigmus wachtli Seitner (Hymenoptera: Torymidae), or on the inner side of scales of partly open cones. A recently discovered egg parasitoid belonging to the genus Telenomus has been shown to attack bug eggs in both oviposition sites. In this paper we investigated the parasitoid performance according to oviposition sites. Field samplings were conducted in two evergreen cypress orchards located in the south of France. The distribution and condition of the egg patches were compared between the two locations and oviposition sites. Seed bugs preferred to oviposit in emergence holes of M. wachtli, and parasitoid performance was higher in eggs laid on cone scales. The chalcid emergence holes seemed to ensure bug eggs with enemy-free space. Oviposition site selection could be an adaptive strategy to escape parasitoid attack.

Optimal patch time allocation for time-limited foragers

The Charnov Marginal Value Theorem (MVT) predicts the optimal foraging duration of animals exploiting patches of resources. The predictions of this model have been verified for various animal species. However, the model is based on several assumptions that are likely too simplistic. One of these assumptions is that animals are living forever (i.e., infinite horizon). Using a simple dynamic programming model, we tested the importance of this assumption by analysing the optimal strategy for time-limited foragers. We found that, for time-limited foragers, optimal patch residence times should be greater than those predicted from the classic, static MVT, and the deviation should increase when foragers are approaching the end of their life. These predictions were verified for females of the parasitoid Anaphes victus (Hymenoptera: Mymaridae) exploiting egg patches of its host, the carrot weevil Listronotus oregonensis (Coleoptera: Curculionidae). As predicted by the model, females indeed remained for a longer time on host patches when they approached the end of their life. Experimental results were finally analysed with a Cox regression model to identify the patch-leaving decision rules females used to behave according to the model’s predictions.

Oogenesis in Hydra: Nurse cells transfer cytoplasm directly to the growing oocyte

Oogenesis in Hydra occurs in so-called egg patches containing several thousand germ cells. Only one oocyte is formed per egg patch; the remaining germ cells differentiate as nurse cells (Miller et al., Dev. Biol. 224 326–338 (2004)). Whether and how nurse cells contribute cytoplasm to the developing oocyte has been unclear. We have used tissue maceration to characterize the differentiation of oocytes and nurse cells in developing egg patches. We show that nurse cells decrease in size at the same time that developing oocytes increase dramatically in volume. Nurse cells are also tightly attached to oocytes at this stage and confocal images of egg patches stained with the fluorescent membrane dye FM 4–64 clearly show large gaps (10 μm) in the cell membranes separating nurse cells from the developing oocyte. We conclude that nurse cells directly transfer cytoplasm to the developing oocyte. Following this transfer of cytoplasm, nurse cells undergo apoptosis and are phagocytosed by the oocyte. These results demonstrate that basic mechanisms of alimentary oogenesis typical of Caenorhabditis and Drosophila are already present in the early metazoan Hydra.

Egg load of lab-cultured Anaphes iole and effects of mate presence and exposure time on load depletion

Anaphes iole Girault (Hymenoptera: Mymaridae) is a solitary egg parasitoid of Lygus bugs (Heteroptera: Miridae) in North America. This research considered factors that might impact the egg load of lab-cultured A .iole females, reared from Lygus hesperus Knight egg patches. The following hypotheses were tested: (1) egg load was related to body size and not affected by female age, and (2) egg load depletion was not affected by mate presence and time (in days) that females were exposed to host patches. Initial egg load averaged 48 mature eggs and no immature eggs were detected in the ovarioles of dissected females. Egg load was neither related to body size (hind tibia or forewing length) nor affected significantly by age (0, 1 or 2days old honey-fed females). Mate presence (females with or without males) and exposure time (1, 3 or 5days on the same host patch) had no effect on egg load depletion. Females usually depleted most of their egg load within 24h. From 86 to 92% of females contained less than six mature eggs and no immature eggs after 1, 3 or 5days of exposure to host patches. The results of this study suggest that A. iole females are certainly pro-ovigenic and initial egg load does not correlate with body size or age. Since mated and unmated females deplete most of their egg load in 24h, time-efficient production of progeny may result when ovipositing parasitoids are exposed to suitable hosts for just a few days.

Fine scale spatial pattern of Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax) eggs

AbstractPacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax) eggs exhibited different spatial structure on the scale of 0.75–2.5 km in two egg patches sampled in the Southern California Bight in April 2000. Plankton samples were collected at 4‐min intervals with a Continuous Underway Fish Egg Sampler (CUFES) on 5 × 5 km grids centered on surface drifters. Variograms were calculated for sardine and anchovy eggs in Lagrangian coordinates, using abundances of individual developmental stages grouped into daily cohorts. Model variograms for sardine eggs have a low nugget effect, about 10% of the total variance, indicating high autocorrelation between adjacent samples. In contrast, model variograms for anchovy eggs have a high nugget effect of 50–100%, indicating that most of the variance at the scales sampled is spatially unstructured. The difference between observed spatial patterns of sardine and anchovy eggs on this scale may reflect the behavior of the spawning adults: larger, faster, more abundant fish may organize into larger schools with greater structure and mobility that create smoother egg distributions. Size and mobility vary with population size in clupeoids. The current high abundance of sardines and low abundance of anchovy off California agree with the greater autocorrelation of sardine egg samples and the observed tendency for locations of anchovy spawning to be more persistent on the temporal scale of days to weeks. Thus the spatial pattern of eggs and the persistence of spawning areas are suggested to depend on species, population size and age structure, spawning intensity and characteristic physical scales of the spawning habitat.