Synchrony Of Emergence Research Articles

Budburst Phenology, Plant Vigor, and Host Genotype Effects on the Leaf-Galling Generation ofCallirhytis cornigera(Hymenoptera: Cynipidae) on Pin Oak

Densities of Callirhytis cornigera (Osten Sacken), a cynipid with alternating agamic and sexual generations that develop in woody stem galls and blister-like leaf galls, respectively, often vary among neighboring pin oaks, Quercus palustris Muenchhausen. We studied the ovipositional behavior of agamic wasps and tested several hypotheses to explain intraspecific variation in susceptibility to leaf gall induction. Agamic females laid eggs primarily into green-tip buds. Heavily galled trees had proportionately more vulnerable buds than lightly galled trees during peak oviposition in 1998, supporting the phenological synchrony hypothesis, but not in 1999. Contrary to plant vigor hypothesis predictions, rates of shoot or leaf expansion were similar for lightly and heavily galled trees. Agamic wasps were transferred from heavily infested trees onto shoots of heavily or lightly infested novel trees, or back onto their natal trees, to test for inherent differences in susceptibility to leaf galling. Leaf gall induction was greater on natal than novel trees in 1997, supporting the demic adaptation hypothesis, and there was a trend for greater leaf gall induction on heavily galled than lightly galled novel trees. These patterns, however, did not reoccur in 1998. Although synchrony of emergence with budburst is critical to ovipositional success of agamic C. cornigera, other host-related factors, including those affecting stem gall induction or survival of the agamic generation, probably are more important in determining variation in tree infestation levels. Once a suitable host is colonized, limited wasp dispersal may also contribute to buildup of insular populations on particular trees.

Germination and Emergence of Parsley in Response to Osmotic or Matric Seed Priming and Treatment with Gibberellin

`Moss Curled' seeds of parsley (Petroselinum crispum L.) were primed osmotically in polyethylene glycol or matrically in fine, exfoliated vermiculite at –0.5 MPa for 4 or 7 days at 20 or 30 °C with 0 or 1 mm GA3. All priming treatments stimulated and hastened germination. Matric priming resulted in greater germination (89%) than osmotic priming (83%) when seeds were primed for 7 days at 30 °C, but priming agent had no effect on germination percentage following priming at 20 °C or for 4 days. In seeds primed for 4 days at 20 or 30 °C, matric priming hastened germination more than did osmotic priming. Germination was generally less synchronous with matric than with osmotic priming. Increasing priming time from 4 to 7 days increased the rate of germination, but increased germination synchrony only when seeds were primed at 20 °C. Inclusion of 1 mm GA3 during priming had little or no effect on germination. All matric priming treatments (other than 4-day priming) were repeated to assess seedling emergence in a greenhouse (25°C day/22 °C night). Priming increased the percentage, rate and synchrony of emergence, and increased hypocotyl length at 3 weeks after planting. Priming at 30 °C with 1 mm GA3 resulted in the greatest emergence percentage, hypocotyl length, and shoot dry weight. We conclude that matric priming is a satisfactory alternative to osmotic priming of parsley seeds. Chemical name used: gibberellic acid (GA3).

Synchronous activity in the visual system.

Synchronous activity among ensembles of neurons is a robust phenomenon observed in many regions of the brain. With the increased use of multielectrode recording techniques, synchronous firing of ensembles of neurons has been found at all levels in the mammalian visual pathway, from the retina to the extrastriate cortex. Here we distinguish three categories of synchrony in the visual system, (a) synchrony from anatomical divergence, (b) stimulus-dependent synchrony, and (c) emergent synchrony (oscillations). Although all three categories have been well documented, their functional significance remains uncertain. We discuss several lines of evidence both for and against a role for synchrony in visual processing: the perceptual consequences of synchronous activity, its ability to carry information, and the transmission of synchronous neural events to subsequent stages of processing.

Larval growth and development of the stonefly Pteronarcys californica (Insecta: Plecoptera) in the Crowsnest River, Alberta

We used head-capsule width, wing-pad length, larval recruitment, adult emergence, and MULTIFANTM analysis to determine the life history of the stonefly Pteronarcys californica in the Crowsnest River, Alberta. Embryonic development, incorporating an early diapause, accounts for approximately 1 year of the life cycle. Both sexes spend a further 4 years in the larval stage. Female larvae grow faster than males and so achieve a larger size at emergence. Extended larval recruitment leads to variation in the sizes of larvae of the same year class and probably to cohort splitting. There is a high degree of synchrony in adult emergence, perhaps as a result of a summer diapause in antepenultimate-instar larvae. These phenomena (embryonic diapause, extended larval recruitment, different growth rates of the sexes, cohort splitting, and larval diapause) are possibly typical of aquatic insects with long life cycles.

Model Analysis of Spatial Patterns in Mountain Pine Beetle Outbreaks

The mountain pine beetle [MPB,Dendroctonus ponderosaeHopkins (Coleoptera: Scolytidae)] is an aggressive bark beetle, one that typically needs to kill host trees in order to successfully reproduce. This ecological adaptation has resulted in an organism that is both economically important and ecologically significant. Even though significant resources have been expended on MPB research, and a great deal of knowledge exists regarding individual aspects of MPB ecology, some of the most basic questions regarding outbreaks remain unanswered. In our opinion, one reason for the lack of synthesis and predictive power is the inadequate treatment of spatial dynamics in outbreak theories. This paper explicitly addresses the role of spatial dynamics in the precipitation and propagation of MPB outbreaks. We first describe a spatially dynamic model of the MPB/forest interaction that includes chemical ecology, spatial redistribution of beetles, attack, and resulting host mortality. The model is a system of 6 coupled, partial differential equations with 7 state variables and 20 parameters. It represents an attempt to capture the relatively complex predator/prey interaction between MPB and host trees by including the minimum phenomenological descriptions necessary for ecological credibility. This system of equations describes the temporal dynamics of: beetle attraction as a function of pheromone concentration; the change in numbers of flying and nesting beetles; tree resistance/susceptibility; and tree recovery from attack. Spatial dynamics are modeled by fluxes due to gradients in pheromones and kairomones, and the random redistribution of beetles in absence of semiochemicals. We then use the parameterized model to explore three issues central to the ecology of MPB/forest interaction. The first of these is in response to the need for objective ways to compare patterns of successful beetle attacks as they evolve in space. Simulation results indicate that at endemic levels, the pattern of successful attacks are determined almost exclusively by the underlying distribution of susceptible host trees (environmental determinism). As an outbreak develops, the pattern of successfully attacked trees switches to one that is dynamically driven by the self-generated semiochemical landscape (dynamic determinism). This switch from an environmentally determined spatial pattern to a dynamically driven pattern is the hallmark of an outbreak. We discuss the application of a spatial correlation coefficient that can be used to differentiate between the spatial distribution of killed trees in endemic and outbreak phases. The second issue we address through simulation is synchrony in adult emergence. Synchronous adult emergence is critical for the mass attack strategy necessary for overcoming tree defenses. Results from these simulations indicate that the degree of synchrony in adult emergence can have important consequences for assessing the risk of an outbreak. The final issue we investigate through simulation is the effect of spatial pattern of nurse trees (those successfully attacked the previous year) on outbreak potential. Simulations indicated that the spatial proximity of nurse trees was an important determinant of subsequent successful attacks. We conclude with a discussion of the general implications of our simulation experiments.

The Effects of Snake Predation on Metamorphosis of Western Toads,Bufo boreas(Amphibia, Bufonidae)

AbstractFor some anuran species, synchronous metamorphosis may function as an antipredator adaptation by swamping predators during the period of transformation. We examined the levels of synchrony of emergence from the water of metamorphosing western toads (Bufo boreas) in the presence and absence of a live snake predator, the common garter snake (Thamnophis sirtalis) in a laboratory experiment. To compare between the treatments, we measured the time to emergence from the water, the number of metamorphs emerging together, and the level of aggregation (before and during emergence) of the toads in each treatment. There was a difference between the treatments when all three factors were considered. We attributed these differences to a behavioral response in whichB. boreasemerged sooner in the presence of the predator, regardless of whether individual toads had reached the point at which they were physically better suited to the terrestrial environment than the larval environment.

Perfectionnement des méthodes de production et de lâcher deCotesia melanoscela, parasite de début de saison deLymantria dispar

Rearing and release procedures forCotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae), an early-season parasitoid ofLymantria dispar (L.), were evaluated in 1995 and 1996 at the Beltsville Agricultural Research Center, Beltsville, Maryland, USA. Mass rearing procedures were developed during the winter/spring of 1995/1996 to produce diapausingC. melanoscela cocoons for experimentation. Program efficiency as measured by percent adult emergence was estimated to be 84% with a measured sex ratio of 48:52 M:F, at an estimated cost per 1 000 cocoons of U.S. $5.26 for materials and a labor requirement of approximately 6 hours. A host larvae:female parasitoid ratio of 100:1 was found to be most efficient in terms of number of parasitoid cocoons produced per female parasitoid, but a ratio of 100:2 was most efficient in terms of number of cocoons per rearing cup. OverwinteringC. melanoscela cocoons under natural conditions for 25 weeks (November placements) before expectedL. dispar egg hatch (mid-April) resulted in excellent synchrony with host egg hatch. Alternatively, holdingC. melanoscela cocoons in cold storage for 23 or more weeks at 5°C resulted in adult parasitoid emergence beginning 10 days after removal from cold storage, and proper timing of removal would result in similar synchrony of adult emergence with host egg hatch. These alternative release strategies give managers increased program flexibility.

Evaluating the Dynamics of Unintended Interpersonal Coordination

Past research has shown that interpersonal interactions are characterized by a tacit coordination of motor movements of the participants and has suggested that the emergent synchrony might be explained by a coupled oscillator dynamic. This study investigates whether unintended between-person coordination can be demonstrated in a laboratory task that will allow an evaluation of whether such dynamical processes are involved. Ten pairs of participants performed a simple rhythmic task in which they had visual information about each other's movements but had no goal to coordinate. A cross-spectral analysis of the movements revealed higher coherence and a distribution of relative phase angles that was dominated by values near 0 deg. and 180 deg. These results support the hypothesis that dynamical organizing principles are involved in natural interpersonal synchrony.

Mating structure and sex ratio variation in a natural population ofNasonia vitripennis

We use allozyme polymorphism to estimate foundress numbers and inbreeding in a Swedish population of the parasitoid wasp Nasonia vitripennis and compare observed sex ratios with the predictions of local mate competition theory. Foundress numbers per host patch estimated from electrophoretic data range from one to nine, with an arithmetic mean of 2.3 and a harmonic mean of 1.49. The inbreeding coefficient calculated directly from the genetic data (F = 0.312) was in agreement with that estimated from the foundress number distribution (F = 0.336). The proportion of males per patch increased as predicted by the estimated foundress numbers and the level of inbreeding, particularly when minimum numbers of males per brood and synchrony of emergence are taken into account. Superparasitism was more frequent than expected from experimental studies. The mating structure of this population implies that it is probably under selection for both female-biased sex ratios and facultative sex ratio behaviour because of variable opportunities for outbreeding.

Panicle emergence of tiller types and grain yield of tiller order for direct-seeded rice cultivars

Grain yield of rice ( Oryza sativa, L.) tillers is critical to rice crop yield and quality but relatively little is known about variations that occur among panicles and grains for tiller types and emergence orders of direct-seeded rice cultivars. The objective of research was to examine how tillering may affect yield and quality at low plant population densities with profuse tillering. Single rice plants were grown in pots in a greenhouse in 1990 and in 1992 and in the field in 1991. The aim was to maximize tillering and thus better see effects of tiller emergence order and type on yield and panicle emergence. Culm and panicle emergence dates were successively later for primary, secondary, and tertiary tillers but with a smaller delay among panicle emergence dates than was observed for tiller emergence. Grain yield of tillers was related more to emergence order than to tiller type. Secondary and tertiary tillers in sufficient numbers could cause delays in crop grain maturity. Specifically, the beginning of grain-filling (closely following top anthesis) was 1 to 5 d later for primary tillers and 3 to 9 d later for secondary tillers, compared to main stems. These data indicate direct-seeded rice cultivars have partial but not complete synchrony of panicle emergence. Consequently, production strategies that increase preflood N to increase tillering in thin (sparsely populated) rice stands, could potentially delay maturity of the crop as well as increase yields.

Gibberellic acid during priming ofEchinacea purpurea(L.) Moench seeds improves performance after seed storage

SummarySeed of purple coneflower (Echinacea purpurea) primed at –0.4 MPa (15°C, 10 d in darkness) either matrically in fine exfoliated vermiculite or osmotically in polyethylene glycol had higher rate, synchrony and percentage of seedling emergence than non-primed seeds. Inclusion of 10−6 M gibberellic acid (GA3) during priming enhanced the benefits of priming by increasing further the emergence rate and synchrony, seedling shoot dry weight, and petiole and lamina lengths of the first true leaf. Inclusion of 10−2 M ethephon, alone or with GA3, during priming had no effect on subsequent seed germination or seedling emergence. Primed seeds stored at high or low moisture concentrations for one month at 4° or 20°C, compared with freshly primed seeds, showed no reduction in rate, synchrony or percentage of seedling emergence. Matric priming, compared with osmotic priming, reduced the amount of GA3 per seed needed during priming to give similar germination benefits and avoided post-transplanting plant lodging a...

Emergent synchrony in locally coupled neural oscillators

The discovery of long range synchronous oscillations in the visual cortex has triggered much interest in understanding the underlying neural mechanisms and in exploring possible applications of neural oscillations. Many neural models thus proposed end up relying on global connections, leading to the question of whether lateral connections alone can produce remote synchronization. With a formulation different from frequently used phase models, we find that locally coupled neural oscillators can yield global synchrony. The model employs a previously suggested mechanism that the efficacy of the connections is allowed to change on a fast time scale. Based on the known connectivity of the visual cortex, the model outputs closely resemble the experimental findings. Furthermore, we illustrate the potential of locally connected oscillator networks in perceptual grouping and pattern segmentation, which seems missing in globally connected ones.

Effect of seasonal placement ofCotesia melanoscela (Hym.: Braconidae) on its potential for effective augmentative release againstLymantria dispar (Lep.: Lymantriidae)

Cohorts ofCotesia melanoscela (Ratzeburg) (Hymenoptera: Braconidae) cocoons were exposed in the field at three Maryland locations to attack by natural enemies for two week periods, then were held in an outdoor insectary untilC. melanoscela adult or hyperparasitoid emergence. The timing of placement of theC. melanoscela cocoons in the field had a profound effect on the number ofC. melanoscela that survived and emerged as adults in synchrony with the field occurence of susceptible early-instarLymantria dispar (L.) larvae. The proportion of emerged adults available during susceptible host stages ranged from 1–92%, depending on dates of release. November or December placements ofC. melanoscela cocoons were most effective with 74–92 % emergence of adults during peak periods of susceptible host stages. Spring placements were least effective. The causes of ineffective placement, which varied with location and with date, were program (handling) loss, non-emergence, attack by hyperparasitoids, predation, andC. melanoscela adult emergence at times when appropriateL. dispar life stages would not be present. We concluded that November/December releases avoided natural enemies and promoted appropriate diapause and post-diapause development that enhanced survival and synchrony of adult emergence with host stage susceptibility.

Matric and osmotic priming of Echinacea purpurea (L.) Moench seeds

Purple coneflower seeds ( Echinacea purpurea (L.) Moench) following osmotic priming in polyethylene glycol (PEG) or matric priming in expanded vermiculite had greater rate, synchrony and percentage of germination at 20° C than non-primed seeds. Osmotic or matric priming for 10 days at −0.4 MPa and 15° C resulted in higher germination rate and percentage than shorter (5 day) exposure or lower (−1.5 MPa) water potential. Seedling emergence rate, synchrony and percentage from osmotically or matrically primed seeds were similar in both cool (23–27° C day) and warm (35–40° C) glasshouse regimes. Emergence was faster from primed than from non-primed seeds in both regimes. Emergence percentage was higher (80%) from primed seeds than from non-primed seeds (50%) in the cool regime but emergence synchrony was unaffected. In the warm regime, primed seeds emerged more synchronously than non-primed seeds but emergence percentage was unaffected. Moistened vermiculite substituted for PEG solution as a priming medium for purple coneflower seeds since benefits to seed germination or seedling emergence following priming (−0.4MPa, 15° C, 10 days, darkness) in these media were similar.

Summer Emergence of Mayflies, Stoneflies, and Caddisflies from a Colorado Mountain Stream

The summer emergence patterns of mayfly, stonefly, and caddisfly species are described for a second order, southern Rocky Mountain Colorado stream. Frequent, standardized, sweepnetting and emergence trap samples provided 1,779 adults of 45 taxa consisting of 11 mayfly, 15 stonefly, and 19 caddisfly species. The five most dominant species were, in order of importance, Suwallia nr. lineosa, Sweltsa coloradensis, Oligophlebodes minutus, Paraleuctra vershina, and Baetis bicaudatus. Stoneflies contributed 70% of all adults collected. Peak species richness of all orders occurred near the summer solstice and maximum water temperatures. The range of slope values generated by simple linear regression of cumulative percentage catch revealed that emergence was extended (slopes < 4%/day) for five of the seven most abundant species. Two caddisflies, 0. minutus and Rhyacophila pellisa, displayed a synchronous emergence pattern. This study adds 35 new records for the Rio Conejos drainage and Conejos County and provides a baseline of comparison against future changes in species richness among these orders. Mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera) are among the dominant insect orders in Rocky Mountain stream ecosystems, yet there are no published accounts of the species-level diversity or emergence phenology of all three groups in any stream of the region. Ward and Kondratieff (1992) state that most of the comprehensive knowledge of aquatic insects in Colorado has been amassed only recently, and that much work on insect life histories and distribution patterns remains to be conducted. Emergence is an important aspect of the life histories of aquatic insects in that it sets the stage for the next generation (Corbet, 1964; Sheldon and Jewett, 1967). Patterns of emergence may affect the allocation of resources and avoidance of competition through temporal segregation of morphologically or functionally similar species (Grant and Mackay, 1969). Corbet (1964) described four types of emergence patterns: continuous, rhythmic, sporadic, and seasonal. Most aquatic insects of high latitudes and altitudes exhibit a seasonal emergence pattern. The interaction of temperature, photoperiod, and local climate conditions helps to determine aquatic insect seasonal phenology in temperate regions (Masteller, 1983, 1993). Our objectives were to characterize the summer emergence patterns and emergence synchrony of the adult mayflies, stoneflies, and caddisflies in Massey Gulch, a small tributary of the Rio Conejos of south-central Colorado. There are no published reports of previous collections or studies of this stream. Few species records are available for the Rio Grande, Rio Conejos, and adjacent streams of the San Juan Mountains (Stark et al., 1973a, 1973b; Baumann et al., 1977; and Szczytko and Stewart, 1979 for stoneflies; Herrman et al., 1986 for caddisflies; Ward and Kondratieff, 1992; McCafferty et al., 1993 for mayflies). MATERIALS AND METHODS-Massey Gulch is a second-order stream located at 106015'W longitude and 37*03'N latitude. Emergence was monitored along an approximate 100 m stretch of the stream about 1.5 km upstream from its confluence with the Rio Conejos, 23 km west of Antonito, Colorado. The stream was no more than 3 m wide, and it had a permanent flow at this 2,700 m elevation, mixed-coniferous forest site. A Ryan@ model J, continuous recording thermograph was placed in the stream on 21 May 1989 and This content downloaded from 157.55.39.92 on Wed, 22 Jun 2016 06:59:02 UTC All use subject to http://about.jstor.org/terms 250 The Southwestern Naturalist vol. 39, no. 3 ou 14 , S12 _/^// I V'

Predicted changes in the synchrony of larval emergence and budburst under climatic warming.

The impact of climatic warming on the synchrony of insect and plant phenologies was modelled in the case of winter moth (Operophtera brumata) and Sitka spruce (Picea sitchensis) in the Scottish uplands. The emergence of winter moth larvae was predicted with a thermal time requirement model and the budburst of Sitka spruce was predicted from a previously published model (Cannell and Smith 1983) based on winter chilling and thermal time. The date of emergence of winter moth larvae was predicted to occur earlier under climatic warming but the date of budburst of Sitka spruce was not greatly changed, resulting in decreased synchrony between larval emergence and budburst. The general question of how a change of climate might affect phenological synchrony and insect abundance is discussed.

Seedling emergence and economic yield from osmotically primed or hydrated seeds of carrot (Daucus carotaL.)

SummarySeedling emergence and plant growth from primed or 100% germinated seeds that were fluid drilled were compared with those from primed or untreated seeds sown dry over three sowing dates in the field. Seedlings from treated seeds emerged more rapidly than those from untreated seeds but seed treatments had no effect on emergence synchrony or percentage. Seedling fresh weights were affected little by seed treatments. Only from the third sowing were root fresh weights greater from fluid-drilled seeds than from dry-sown seeds. Under glasshouse conditions, seeds given a hydration treatment (one-day water soak at 20°C followed by three-day incubation in fluid drilling gel at 20°C) generally emerged more rapidly and gave greater seedling fresh weights than primed seeds when seeds of both treatments were fluid-drilled. Incorporation of 15 gof 9N-19.8P-12.5 K fertilizer per litre of fluid drilling gel increased shoot fresh weight compared with untreated, primed or hydrated seeds under glasshouse conditions. ...

Seedling Emergence and Yield from Hydrated Collard Seeds Fluid-drilled in High-phosphorus Gel

Seeds of `Champion' collard (Brassica oleracea L. var. acephala) were hydrated in water or a fluid-drilling gel (N-gel, hydroxyethyl cellulose) for 1 or 2 days at 20C (50 seeds/ml) before they were fluid-drilled into peat-lite in a greenhouse. Time to 50% seedling emergence from these seeds was more than 2 days earlier than from dry-sown untreated seeds, although emergence synchrony and percentage were unaffected. A second greenhouse study revealed more rapid seedling emergence from hydrated seeds that then were fluid-drilled than from dry-sown untreated seeds even when the delivery gel contained up to 25 g 9N-19.8P-12.5K/liter. Increasing fertilizer from 5 to 25 g·liter-1 led to increased shoot fresh weight 6 weeks after planting. When sown on two dates into field plots, hydrated seeds (1 day in either water or gel at 20C, 50 seeds/ml) that were fluid-drilled in 1.5% (w/v) N-gel containing 5 or 15 g 9N-19.8P-12.5K/liter yielded 42% greater final shoot fresh weights than untreated seeds sown dry.

The biology of Anthrenus sarnicus Mroczkowski (Coleoptera: Dermestidae): I. Egg and larval development

Egg hatch in Anthrenus sarnicus Mroczkowski occurred over the temperature range 15–32.5°C with the highest percentage hatch of 85% at 25°C. The incubation period between the highest and lowest temperature ranged from 10 to 44 days respectively. Increase in humidity tended to decrease the duration of the egg stage. When reared on a diet consisting of fishmeal, yeast and cholesterol under constant temperature and humidity conditions in darkness, at temperatures above 15°C, the majority of larvae pupated between 38 and 60 weeks, but a small proportion took up to 92 weeks. At 25°C 70% r.h., 5% of larvae pupated after only 12–13 weeks. At 15°C pupation was bimodal, with the first period between weeks 54 and 60 and the second between weeks 90 and 110. When larvae were reared in a room where they were subjected to naturally fluctuating temperature, humidity and photoperiod, pupation was markedly synchronous compared to larvae under the same conditions but kept in constant dark. These results strongly suggested that synchrony in adult emergence is determined by the effects of seasonal changes in photoperiod on diapause induction and termination. Rearing larvae in a pigeon loft showed that successful completion of the life cycle can occur in outdoor conditions in southern England. Under such conditions the life cycle took either 1 or 2 years depending upon the time in the year when egg hatch occurred and temperature conditions during the active larval growth periods. Interactive effects of photoperiod and temperature on diapause development strongly synchronized adult emergence. Successful larval development occurred on a wide range of dried animal materials which could be found in museums and domestic environments.

Density‐Dependent Cannibalism in Larval Dragonflies

Cannibalism is a likely mechanism of population regulation in dragonflies that inhabit fish—free temporary ponds. I tested for density—dependent effects of cannibalism on survival and size structure of larvae of the dragonfly Tramea carolina in two short—term experiments in replicated artificial ponds. I was able to distinguish mortality due to cannabalism from other sources of mortality by preventing some populations from engaging in cannibalism. The first experiment included two density levels and the presence or absence of cannabilism in a factorial design. The no—cannibalism treatment was achieved by removing the labial palps from all individuals to prevent them from grasping large prey. T. carolina survived significantly better in the no—cannibalism populations at both densities, and this difference was greater at high density than low density, indicating that the proportion cannibalized was density dependent. A second experiment explored the form of the density—dependent cannibalism curve over a broad range of density. The results were adequately fitby a predator—prey model incorporating size structure, so that not all members of the population were vulnerable to cannibalism. In both experiments the survival of only the smaller instars was reduced, suggesting that cannibalism may reduce variation in the size distributions of dragonfly populations and contribute to emergence synchrony. The results demonstrated that cannibalism was strongly density dependent and may contribute to population regulation of dragonflies in temporary ponds.