Peak Emergence Research Articles

Duration of Pseudacteon curvatus Borgmeier (Diptera: Phoridae) Pupal Stages at Reduced Temperatures

Duration times were determined for Pseudacteon curvatus Borgmeier pupae subjected to various temperature regimes. Pupae that had initially developed 12–15 d in parasitized fire ant, Solenopsis invicta Buren, workers held at ~27°C were collected and subsequently held at different temperature regimes. Pupae exposed to a temperature of 26.7°C had the earliest peak fly emergence 15 d later. Pupae exposed to a lower temperature of 18.3°C for 12 or 19 d and then exposed to a temperature of 26.7°C required an additional 7 and 11 d to peak fly emergence, respectively. At 18.3°C peak fly emergence was delayed an additional 20 d. At 10°C for 12 or 19 d followed by 26.7°C, peak fly emergence was delayed an additional 12 and 18 d, respectively. Holding pupae at 10°C for 54 d followed by 26.7°C delayed peak fly emergence by an additional 51 d with a correspondingly high mortality. Fly survival rates tended to decrease as peak emergence was delayed. Models that predict fly emergence when pupae are held at reduced temperatures will prove useful in rearing programs where extended storage of phorid fly pupae is necessary for optimizing releases.

Emergence Cues Of A Mayfly In A High-Altitude Stream Ecosystem: Potential Response To Climate Change

To understand the consequences of human accelerated environmental change, it is important to document the effects on natural populations of an increasing frequency of extreme climatic events. In stream ecosystems, recent climate change has resulted in extreme variation in both thermal and hydrological regimes. From 2001 to 2004, a severe drought in western United States corresponded with earlier emergence of the adult stage of the high-altitude stream mayfly, Baetis bicaudatus. Using a long-term database from a western Colorado stream, the peak emergence date of this mayfly population was predicted by both the magnitude and date of peak stream flow, and by the mean daily water temperature, suggesting that Baetis may respond to declining stream flow or increasing water temperature as proximate cues for early metamorphosis. However, in a one-year survey of multiple streams from the same drainage basin, only water temperature predicted spatial variation in the onset of emergence of this mayfly. To decouple the effects of temperature and flow, we separately manipulated these factors in flow-through microcosms and measured the timing of B. bicaudatus metamorphosis to the adult stage. Mayflies emerged sooner in a warmed-water treatment than an ambient-water treatment; but reducing flow did not accelerate the onset of mayfly emergence. Nonetheless, using warming temperatures to cue metamorphosis enables mayflies to time their emergence during the descending limb of the hydrograph when oviposition sites (protruding rocks) are becoming available. We speculate that large-scale climate changes involving warming and stream drying could cause significant shifts in the timing of mayfly metamorphosis, thereby having negative effects on populations that play an important role in stream ecosystems.

Role of juvenile hormone esterase and epoxide hydrolase in reproduction of the cotton bollworm, Helicoverpa zea

The role of juvenile hormone (JH) esterase (JHE) and epoxide hydrolase (EH) in reproduction of the cotton bollworm, Helicoverpa zea, was investigated. Peak emergence of male and female bollworm adults occurred early in the scotophase. Female adults were added to males in a 1:2 ratio, respectively, at the beginning of the first photophase after emergence (d0). The highest oviposition rates for mated females were noted on d 2–4. The in vitro JH III esterase and JH III EH activity was measured in whole body homogenates of virgin and mated females from d0 to d8 post-emergence. Maximal JHE activity for virgin females occurred on d2 (1.09±0.14(±1 SEM) nmol of JH III degraded/min/mg protein), which was approximately twice that of mated females on the same day. The same results were observed for EH where the activity peaked on d2 at 0.053±0.003 as compared to 0.033±0.003 nmol of JH III degraded/min/mg protein, respectively. By d4, both JHE and JH EH activities declined significantly in virgin and mated females and were the same through d7. The developmental changes and effects of mating on JH degradation were similar when measured per insect. The highest levels of JHE and JH EH activity/min/mg protein in d2 virgin and mated females was found in ovaries followed by the carcass and then haemolymph; no EH activity was found in haemolymph as expected. For ovary, the JHE and JH EH activity was highest in virgin compared to mated females. The role of both enzymes in the regulation of reproduction is discussed.

Phenology of first and peak emergence of Aphthona lacertosa and A. nigriscutis: Two flea beetles introduced for biological control of leafy spurge, Euphorbia esula L.

Nonlinear models were used to estimate first emergence and peak abundance dates for Aphthona lacertosa Rosenhauer and A. nigriscutis Foudras, two flea beetles introduced to control leafy spurge, Euphorbia esula L., in North America. For model development, 26 field sites were sampled for flea beetle abundance at weekly intervals for eight weeks in three western Minnesota counties in 2000, 2001, and 2002. A three-parameter Weibull function, fit to observed cumulative probability distributions, were used to predict accumulated degree-days (ADD) to first emergence. Bias testing indicated the Weibull function provided a useful estimate of first emergence for A. lacertosa (304 ADD, lower developmental threshold 7.5 °C), but failed to produce a useful estimate for A. nigriscutis. A third-order polynomial was used to approximate seasonal abundance and predict peak abundance for each species. Estimated ADD to peak abundance of A. lacertosa was 594 ± 24 (DD > 7.5 °C) and 670 ± 15 (DD > 9.3 °C) for A. nigriscutis. Models were validated with additional data sets from Minnesota, Montana, and North Dakota. Estimated date of peak emergence provided useful predictions of peak emergence for Minnesota and North Dakota, but failed to predict peak emergence in Montana. We speculate that variation in climate and environmental conditions between Midwestern states and Montana were responsible for differing emergence patterns. We conclude that phenology models should be developed regionally to provide useful predictions of peak emergence for land managers. Maps were developed for Minnesota to spatially display predicted dates of peak abundance for A. lacertosa and A. nigriscutis.

Mountain pine beetle population sampling: inferences from Lindgren pheromone traps and tree emergence cages

Lindgren pheromone traps baited with a mountain pine beetle (Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae, Scolytinae)) lure were deployed for three consecutive years in lodgepole pine stands in central Idaho. Mountain pine beetle emergence was also monitored each year using cages on infested trees. Distributions of beetles caught in pheromone traps and emergence cages were compared. Each year, mountain pine beetle emergence from infested trees occurred within a 30-d period, although beetles were caught in pheromone traps over a period as long as 130 d. A large proportion of the total number of beetles caught in pheromone traps occurred prior to and following peak emergence from infested trees. Beetles caught in pheromone traps during the main emergence period from infested trees had greater whole-body lipids compared to beetles caught early and late in the flight season. Low lipid content of beetles caught before and after the main emergence period could be the result of a long-distance flight caused by fewer sources of pheromone attraction on the landscape and (or) some proportion of reemerged parents in the sample. Results suggest that pheromone traps disproportionately sample mountain pine beetle populations and that natural pheromone sources may influence the number and timing of beetles caught in synthetically baited traps.

Emergence timing and control of dandelion (Taraxacum officinale) in spring wheat

In the northern region of the northern Great Plains of North America, the relative abundance of dandelion in field crops has increased over the past two decades, and farmers need information to help them to better manage this species and slow its spread. A study was conducted to determine the emergence timing of dandelion from both rootstock and seed, and to investigate the efficacy of preseeding (spring) versus postharvest (autumn) herbicide treatments on dandelion in spring wheat fields. Emergence of dandelion plants from rootstock was very early (mean time to 50% emergence [E50] of 430 growing degree days [GDD] Tbase0 C), while seedling emergence was much later (mean E50of 980 GDD). Dandelion does not have a persistent seed bank, and seedling emergence occurred only after dandelion plants arising from rootstock flowered and shed seed. Herbicide treatments that included glyphosate plus florasulam, glyphosate plus tribenuron, or higher rates of glyphosate alone (≥675 g ae ha−1), provided high levels of dandelion control. Autumn herbicide applications were more effective than spring applications for reducing dandelion infestation levels (both aboveground biomass and density). Autumn herbicide applications came after peak emergence timing for dandelion plants emerging both from rootstock and from seed. Because dandelion is a simple perennial, population spread must be limited by controlling seedlings. Autumn herbicide applications provide control of dandelion seedlings and therefore, should limit dandelion population spread.

Spring Emergence Biology of the Cabbage Seedpod Weevil (Coleoptera: Curculionidae)

The spring emergence biology of Ceutorhynchus obstrictus (Marsham) was investigated in 2003 and 2004 in relation to habitat type, vegetative cover, and soil temperature in the Mixed Grassland Ecoregion of western Canada. Although total emergence extended over 10–12 wk, emergence patterns were very similar in both years with limited emergence occurring for several weeks before and after a large emergence peak of comparatively short duration. In 2003, peak emergence occurred during a 3-wk period from 28 May to 13 June when 97.6% of C. obstrictus were collected; and in 2004, emergence of 55.6% of weevils occurred during the 1-wk period before 4 June. Peak emergence occurred as mean ground temperature (5 cm in depth) reached 15°C. The greatest number of weevils recorded from a single 1-m2 emergence trap was 956. Significantly more weevils emerged from sheltered and intermediately sheltered locations than from open grassy habitats; sheltered areas were predominantly shelterbelts and yard sites of caragana and poplar trees. No weevils emerged from 14 of 106 cages, and all cages were in open grassy habitat. Spring emergence of weevils in open grassy areas occurred slightly before those in sheltered and intermediately sheltered areas. Cages in open grassy habitat had the highest mean temperature as well as the highest maximum and lowest minimum temperatures in each sampling period. Significantly more males than females emerged early in the season, although during peak emergence there was no difference in sex ratio; and after peak emergence, significantly more females than males emerged.

Foraging ecology of the Tokay gecko, Gekko gecko in a residential area in Thailand

Abstract The foraging behavior of Gekko gecko was observed at the visitor complex of the Khao Khiao Open Zoo at the Khao Khiao-Khao Chomphu Wildlife Sanctuary in Chon Buri Province, Thailand. Foraging parameters of G. gecko (foraging period, time spent moving, foraging attempts, foraging success, prey size consumed, and foraging distance) did not vary significantly between males, females, and juveniles. Individuals foraged between 18:01 and 09:00 hrs. Peak emergence time was between 18:01 and 20:00 hrs. Peak retreat time was between 04:01 and 07:00 hrs. Major food items included insects of the orders Lepidoptera, Orthoptera, and Coleoptera. Prey sizes of males, females, and juveniles were not significantly different, indicating no prey size selection. This may have been due to low insect availability in the habitat. Gekko gecko tended to be a sit-and-wait forager spending most of the time waiting for active prey. However, it sometimes foraged more actively when insect abundance was relatively high. Foraging behavior of males tended to be more variable than females and juveniles. In addition, variation in foraging parameters among individuals was noted. Foraging strategies of G. gecko observed in this study are interpreted in the context of optimal foraging theory.

Soil heating and germination: investigations using leaf scorch on graminoids and experimental seed burial

Burns conducted to reduce fuels are usually carried out under mild weather conditions. This introduces a risk that soil heating will be insufficient to trigger germination in species with a heat-shock requirement. Resprouting graminoids with leaves or culms arising from subterranean meristems can be used to estimate soil heating because the leaf is burnt to soil level and the subterranean tissue is killed to a depth dependent on the level of soil heating. Provided the meristem survives, the length of dead tissue is exposed following subsequent growth. We sought to determine whether the length of dead tissue (scorch length) was correlated with the post-fire recovery of Acacia suaveolens, a fire-sensitive shrub with seed germination dependent on heat shock. The peak emergence depth for this species varies as a function of soil heating: temperatures above 100°C induce seed death whereas temperatures below 60°C do not break dormancy. We found that average scorch length was correlated with average seedling emergence depth. However, experimental burial of scarified (i.e. non-dormant) seeds showed that the peak emergence depth was similar for seeds sown before, after or in the absence of fire. This suggests that post-germination mortality is also depth-dependent, with seedling survival reduced at depths from 0 to 20 mm. The results suggest that survival of seedlings will be enhanced if soil heating is sufficient to promote germination of seeds buried at least 20 mm deep. Scorch lengths on graminoid leaves provide an indication of whether this condition is met.

Evaluation of <I>Cuphea</I> as a Rotation Crop for Control of Western Corn Rootworm (Coleoptera: Chrysomelidae)

The ability to prevent significant root feeding damage to corn, Zea mays L., by the western corn rootworm, Diabrotica virgifera virgifera LeConte, by crop rotation with soybean, Glycine max (L.) Merr., has been lost in portions of the Corn Belt because this pest has adapted to laying eggs in soybean fields. Cuphea spp. has been proposed as a new broadleaf crop that may provide an undesirable habitat for rootworm adults because of its sticky surface and therefore may reduce or prevent oviposition in these fields. A 4-yr study (1 yr to establish seven rotation programs followed by 3 yr of evaluation) was conducted to determine whether crop rotation with Cuphea would provide cultural control of corn rootworm. In support of Cuphea as a rotation crop, fewer beetles were captured by sticky traps in plots of Cuphea over the 4 yr of this study compared with traps in corn and soybean, suggesting that fewer eggs may be laid in plots planted to Cuphea. Also, corn grown after Cuphea was significantly taller during vegetative growth, had significantly lower root damage ratings for 2 of 3 yr, and had significantly higher yields for 2 of 3 yr compared with continuous corn plots. In contrast to these benefits, growing Cuphea did not prevent economic damage to subsequent corn crops as indicated by root damage ratings > 3.0 recorded for corn plants in plots rotated from Cuphea, and sticky trap catches that exceeded the threshold of five beetles trap(-1) day(-1). Beetle emergence from corn plots rotated from Cuphea was significantly lower, not different and significantly higher compared with beetle emergence from continuous corn plots for 2002, 2003 and 2004 growing seasons, respectively. A high number of beetles were captured by emergence cages in plots planted to Cuphea, indicating that rootworm larvae may be capable of completing larval development by feeding on roots of Cuphea, although peak emergence lagged approximately 4 wk behind peak emergence from corn. Based on these data, it is unlikely that crop rotation with Cuphea will provide consistent, economical, cultural control of corn rootworm.

Modeling population dynamics of a tea pest with temperature‐dependent development: predicting emergence timing and potential damage

AbstractThe tea leaf roller, Caloptilia theivora Walsingham (Lepidoptera: Gracillariinae), is one of the serious pests of tea plants in Japan. To understand the mechanism of seasonal occurrence of this insect pest, we developed a population dynamics model that explicitly incorporates the temperature‐dependent development of the pest. The model predictions were compared with observed captures in pheromone traps at the experimental site of the Kagoshima Tea Experiment Research Station in Japan. The results showed that the emergence timing of the insect pest observed in the field was determined primarily by temperature. The relationship between the timing of adult emergence and the leaf damage level was also studied using a logistic regression model. The infestation level decreased as the interval between the adult peak emergence date and the date of tea plucking increased, implying that asynchrony between plant phenology and emergence of the insect pest is a critical factor reducing damage level. We examined how the damage level changes according to global warming. Increased temperature made the timing of insect appearance forward and enhance asynchrony of plant–pest phenology. Therefore, reduction of damage level by the insect pest is expected under global warming.

Biological Control of Melanaspis Obscura on Oaks in Northern California

In 1988, Encarsia aurantii (Howard) (Hymenoptera: Aphelinidae) was introduced into northern California to control an isolated infestation of obscure scale, Melanaspis obscura (Comstock) (Coccoidea: Diaspididae), on native and exotic oaks (Quercus spp.) in Sacramento’s Capitol Park. By 2002, there was no longer any need for chemical control of the scale (i.e., complete biological control). Both parasite and host are univoltine; peak emergence of adult parasites coincides with the peak of newly settled, first-instar scales. Increase of the parasite and concomitant decline of the scale from 1992 to 2004 are documented for one native and one exotic oak tree. During spring of 2004, mean density of female scales (based on 100 twigs per tree) on 12 previously infested oak trees was generally low, ranging from <1 (eight trees) to ∼15 (single tree) scales/twig. Mean percentage parasitization (per twig) ranged from ∼30 to ∼85%, and was density independent (spatial context) for each of five trees. Two refuges for the scale population were noted: some scale crawlers settled and developed under the parental scale cover (spatial refuge) and some female scales continued to produce crawlers into late summer and early fall, when adult parasites were no longer available (temporal refuge). This case illustrates how an introduction strategy (i.e., single-species release of E. aurantii), which was derived from an analysis of the parasite guild of the pest, was executed in the field and ultimately led to successful biological control.

Emergence of overwintered and new generation adults of the crucifer flea beetle, Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae)

Spring emergence of the crucifer flea beetle, Phyllotreta cruciferae (Goeze), was investigated in 2003 and 2004 in relation to habitat type, vegetative cover, and soil temperature in the Mixed Grassland Ecoregion of western Canada. Although total emergence extended over 10–12 weeks, emergence patterns were quite similar in both years with limited emergence for several weeks before and after a large emergence peak of comparatively short duration. In each year, peak emergence occurred near the end of May as mean ground temperature reached 15 °C. Approximately 45,000 flea beetles were collected with the greatest number of flea beetles recorded from a single 1 m 2 emergence cage being 3736. Significantly more flea beetles emerged from sheltered locations than from open habitats; sheltered areas were predominantly shelterbelts and yard sites of Caragana and poplar trees. In each year, highest numbers of flea beetles emerged in cages placed in Caragana while the fewest emerged from cages in grassy areas. Consistently more females than males emerged throughout the spring with a sex ratio of approximately 1.5 females: 1 male. Emergence of new generation adults occurred from the middle of August until the end of September; this emergence was delayed and extended in late-seeded canola. Seeding date and rate did not significantly affect the abundance of new generation flea beetles. The sex ratio of new generation adults was approximately 1.2 females: 1 male. Emergence cages could be a useful tool for researchers monitoring year-to-year populations of P. cruciferae but the narrow time frame between spring emergence and crop infestation may restrict the usefulness of this tool for producers.

Estimated Fall Chinook Salmon Survival to Emergence in Dewatered Redds in a Shallow Side Channel of the Columbia River

AbstractFall Chinook salmon Oncorhynchus tshawytscha often spawn in the tailraces of large hydroelectric dams on the Columbia River. Redds built in shallow habitats downstream of these dams may be periodically dewatered as a result of load‐following operations and subsequent changes in water surface elevation before the fry emerge. To determine whether fall Chinook salmon redds in a shallow area subjected to periodic dewatering downstream of Wanapum Dam on the Columbia River produced live fry, we installed seven redd caps and monitored emergence. Large numbers of live fry were captured from the redds between March 9 and May 18, 2003. Estimated survival from egg to fry for these redds, which were dewatered approximately 3.1% of the time during the posthatch intragravel rearing period, ranged from 16.9% to 66.6% and averaged 29.2% (assuming 4,272 viable eggs/redd). The peak emergence date ranged from April 1 to April 29 (average, about April 14). Peak emergence dates corresponded well with predicted emergence dates based on 1,000 accumulated temperature units. For fall Chinook salmon emerging from individual redds the mean fork length for each redd ranged from 38.3 to 41.2 mm, and lengths of fish emerging from individual redds increased throughout the emergence period.

Tangled webs: reciprocal flows of invertebrate prey link streams and riparian zones

Summary1. Streams and their adjacent riparian zones are closely linked by reciprocal flows of invertebrate prey. We review characteristics of these prey subsidies and their strong direct and indirect effects on consumers and recipient food webs.2. Fluxes of terrestrial invertebrates to streams can provide up to half the annual energy budget for drift‐feeding fishes such as salmonids, despite the fact that input occurs principally in summer. Inputs appear highest from closed‐canopy riparian zones with deciduous vegetation and vary markedly with invertebrate phenology and weather. Two field experiments that manipulated this prey subsidy showed that it affected both foraging and local abundance of stream fishes.3. Emergence of adult insects from streams can constitute a substantial export of benthic production to riparian consumers such as birds, bats, lizards, and spiders, and contributes 25–100% of the energy or carbon to such species. Emergence typically peaks in early summer in the temperate zone, but also provides a low‐level flux from autumn to spring in ice‐free streams. This flux varies with in‐stream productivity, and declines exponentially with distance from the stream edge. Some predators aggregate near streams and forage on these prey during periods of peak emergence, whereas others rely on the lower subsidy from autumn through spring when terrestrial prey are scarce. Several field experiments that manipulated this subsidy showed that it affected the short‐term behaviour, growth, and abundance of terrestrial consumers.4. Reciprocal prey subsidies also have important indirect effects on both stream and riparian food webs. Theory predicts that allochthonous prey should increase density of subsidised predators, thereby increasing predation on in situ prey and causing a negative indirect effect via apparent competition. However, short‐term experiments have produced either positive or negative indirect effects. These contrasting results may be due to characteristics of the subsidies and individual consumers, but could also result from differences in experimental designs.5. New study approaches are needed to better determine the direct and indirect effects of reciprocal prey subsidies. Experiments coupled with comparative research will be required to measure their effects on individual consumer fitness and population demographics. Future work should investigate whether reciprocal prey fluxes stabilise linked stream–riparian ecosystems, explore how landscape context affects the magnitude and importance of subsidies, and determine how impacts of human disturbance can propagate between streams and riparian zones via these trophic linkages. Study of these reciprocal connections is helping to define a more holistic perspective of catchments, and has the potential to shape new directions for ecology in general.

Rice Water Weevil (Coleoptera: Curculionidae) Population Dynamics in Louisiana

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, has long been an important pest of rice in the U.S. and has recently emerged as a pest of rice in Asia. A systematic study of the life history and population dynamics of this insect was conducted during the 2002 growing season at the Louisiana State University Rice Research Station, Crowley, Acadia Parish, LA, an area where it is a particularly severe pest. By monitoring weevil populations using collections from overwintering sites, from plots of rice planted throughout the growing season, and from light traps, and by dissecting collected weevils to assess the conditions of their fat bodies, flight muscles and ovaries, we concluded that a portion of the weevil population in Louisiana is univoltine, another portion is bivoltine, and another portion may pass through multiple generations if young rice is continually available. However, only one generation of weevils developed in a single rice field. Adult weevils invaded rice fields in apparently large numbers prior to flooding. Weevils possessing both well-developed ovaries and well-developed flight muscles were found in both light traps and rice plots, suggesting that adults were capable of seeking new habitats by flying if rice plants were not suitable for oviposition. Weevils were able to complete a generation on ratoon-crop rice. The emergence of overwintered weevils started in late March, with peak emergence occurring during April and May. Return to overwintering sites began in early June and continued until October. Weevils appeared to move among overwintering habitats. A comparison of weevil population dynamics in rice plots planted on different dates supported the use of early planting as a management strategy.

Predation on Hatchling and Juvenile Diamondback Terrapins (Malaclemys terrapin) by the Norway Rat (Rattus norvegicus)

Abstract The Norway Rat (Rattus norvegicus) was a major predator on hatchling and juvenile Diamondback Terrapins (Malaclemys terrapin) in a New York population during three years (2001–2003). Rats killed young terrapins by evisceration through the plastron or carapace, exclusively at night, and during two distinct periods: (1) at emergence from nests in August and September; and (2) at emergence from hibernation in April. Predation rates were highest during peak emergence from nests and hibernacula. In the fall, hatchlings were mainly preyed upon within intertidal high marsh vegetation, where hatchlings normally occur after emergence from nests. We found no evidence of rat predation on eggs or hatchlings in nests. Predation in the spring also occurred in the intertidal high marsh, but rats killed juveniles in adjacent terrestrial habitats as well. We used data from a telemetry study of 24 wild hatchlings to estimate rat predation rates. Between 13 September and 22 October 2003, 16 of 24 (67%) radio-tracke...

Genetic diversity of dodder (Cuscuta spp.) collected from commercial cranberry production as revealed in thetrnL (UAA) intron

Swamp dodder (Cuscuta gronovii) is a parasitic plant detrimental to cranberries. Observation of emergence of dodder seeds collected from a cultivated cranberry bog in Massachusetts revealed 2 or more peak emergence times during 4 consecutive growing seasons. Molecular methods were used to investigate genetic variation among the emerging dodder seedlings. On emergence, dodder seedlings were collected and analyzed for DNA sequence diversity in thetrnL (UAA) intron, a noncoding region of chloroplast DNA. DNA sequence analysis of 87 seedlings collected during the 1999 and 2000 growing seasons revealed the presence of 2 dodder ecotypes, designated A and B. Comparative DNA sequence analysis indicated that in thetrnL (UAA) intron, the sequence of ecotype A is identical to that ofCuscuta gronovii, whereas the sequence of ecotype B is closest to that ofCuscuta attenuata (99.3% sequence identity; 293 bases considered). ABg/II restriction enzyme cut site was identified that distinguished between thetrnL (UAA) introns of ecotypes A and B. Restriction fragment length polymorphism (RFLP) was used to analyze the sequences of 100 seedlings collected during the growing seasons of 2001 and 2002. Only 10 of the 187 samples were ecotype A, all of which emerged on or before May 7 in the growing seasons. Therefore, the predominant dodder haplotype found in this study may be a close relative ofC. attenuata and notC. gronovii, the common species found in cranberry bogs.

Temperature-Dependent Development and Prediction of Emergence of the Summer Generation of Plum Curculio (Coleoptera: Curculionidae) in the Southeastern United States

Timely insecticide application against the summer generation (first field generation) of the plum curculio, Conotrachelus nenuphar Herbst, is critical in the production of peach and other stone fruits in the southeastern United States. In the absence of monitoring tools that are effective during midseason when the adults of this generation emerge, a temperature-based emergence model would be useful as an alternative decision aid. In this study, we determined rates of larval development (from oviposition to peak emergence of larvae) and pupal development (from larval emergence to peak emergence of adults) for two populations of C. nenuphar in constant temperatures ranging from &ap;11&ndash;37&deg;C, developed linear regression models to describe the relationships between developmental rate and temperature for both stages, and estimated degree-day requirements for completing development from these models. The lower threshold temperature was 11.1 and 8.7&deg;C for larval and pupal development, respectively. The thermal time requirement from oviposition to peak emergence of larvae was 215.5 DD, and peak emergence of adults occurred 442.4 DD later. For model validation, rearing experiments were carried out with both populations in fluctuating temperatures in the greenhouse and outdoors. Observed degree-day requirements were not significantly different from model-predicted values for larval emergence in the greenhouse and for adult emergence in the greenhouse and outdoors. For larval emergence outdoors, the model overestimated time to peak emergence by &ap;35 DD (2&ndash;3 calendar d), most likely because these trials were carried out during relatively cool conditions in which overestimation by a linear model would not be unexpected. Aspects related to further validation of the model and its use in orchard conditions are discussed.

Resource limitation of diving ducks at Myvatn: Food limits production

We monitored numbers and production of diving ducks on Lake Myvatn and its outlet river, the Laxa, over a period of 25 years, 1975–1999. Aquatic insects, a major food source, were monitored for 23 years, 1977–1999, using window traps. In this paper, we focus on the relationship between the demography of five species of diving ducks and the abundance of aquatic insect species, mainly Chironomidae and Simuliidae. Production of ducks was estimated when most young were 2–4 weeks old, either as young per female (Aythya marila and Aythya fuligula) or as total young found (Melanitta nigra, Bucephala islandica, Histrionicus histrionicus). Variation between years in production of young ducks was strongly correlated with variation in the abundance of aquatic insects. Procladius islandicus and Psectrocladius barbimanus, both of which are univoltine with peak emergence in late July (when many young ducks hatch), as well as the bivoltine Orthocladius consobrinus, showed particularly high correlations with duckling numbers. In one year, 1992, catastrophic weather depressed production. Food appeared to determine production, primarily through its availability to the young. Changes in spring density of breeding ducks of all five species were negatively associated with density in the year before. Resources, estimated as food availability or reproductive success in the year before, were positively correlated with change in breeding numbers in A. marila, A. fuligula and B. islandica. Production three years earlier had a weak but significant effect on change in numbers of M. nigra.