Mean Degree Days Research Articles

Predicted Northward Expansion of the Geographic Range of the Tick Vector Amblyomma americanum in North America under Future Climate Conditions.

Background:The geographic range of the tick Amblyomma americanum, a vector of diseases of public health significance such as ehrlichiosis, has expanded from the southeast of the United States northward during the 20th century. Recently, populations of this tick have been reported to be present close to the Canadian border in Michigan and New York states, but established populations are not known in Canada. Previous research suggests that changing temperature patterns with climate change may influence tick life cycles and permit northward range expansion of ticks in the northern hemisphere.Objectives:We aimed to estimate minimal temperature conditions for survival of A. americanum populations at the northern edge of the tick’s range and to investigate the possibility of range expansion of A. americanum into northern U.S. states and southern Canada in the coming decades.Methods:A simulation model of the tick A. americanum was used, via simulations using climate data from meteorological stations in the United States and Canada, to estimate minimal temperature conditions for survival of A. americanum populations at the northern edge of the tick’s range.Results:The predicted geographic scope of temperature suitability [ annual cumulative degree days (DD) ] included most of the central and eastern U.S. states east of longitude 110°W, which is consistent with current surveillance data for the presence of the tick in this region, as well as parts of southern Quebec and Ontario in Canada. Regional climate model output raises the possibility of northward range expansion into all provinces of Canada from Alberta to Newfoundland and Labrador during the coming decades, with the greatest northward range expansion (up to by the year 2100) occurring under the greenhouse gas (GHG) emissions of Representative Concentration Pathway (RCP) 8.5. Predicted northward range expansion was reduced by approximately half under the reduced GHG emissions of RCP4.5.Discussion:Our results raise the possibility of range expansion of A. americanum into northern U.S. states and southern Canada in the coming decades, and conclude that surveillance for this tick, and the diseases it transmits, would be prudent. https://doi.org/10.1289/EHP5668

Short-term Forecasting of Daily Abundance of West Nile Virus Vectors Culex pipiens-restuans (Diptera: Culicidae) and Aedes vexans Based on Weather Conditions in Southern Québec (Canada).

Since 2002, human cases of West Nile virus (WNV) have occurred every year in southern Canada, but WNV risk remains challenging to predict. Here, we explored the ability of weather-based forecasting models to predict the seasonal abundance of two WNV vector species (Culex pipiens-restuans and Aedes vexans) in Québec, Canada, and explored the importance of accounting for larvicide use and local habitat (forest park vs residential garden). A gamma-generalized linear model predicting mosquito abundance was developed based on an approach previously used in Ontario combining temperature and precipitation during the days preceding mosquito captures. This model was calibrated and validated for each species with independent entomological datasets from the Montréal region collected in 2013 and 2014. Culex pipiens-restuans abundance was associated with mean degree days (dd; >9°C) over the 22 d before mosquito capture and with mean precipitation over the 71 d before capture; Ae. vexans abundance with the mean dd (>12°C) over the 24 d before capture and mean precipitation over the 30 d before capture. These results are consistent with temperature effects on immature development rates and adult activity, and effects of precipitation on the abundance and suitability of breeding sites. Taking into account larvicide use and habitat significantly improved the predictions. This study provides evidence that weather conditions can yield robust short-term predictions of the regional daily mosquito abundance, particularly when accounting for local variation in habitat or mosquito control efforts, and may provide real-time indicators of WNV or other mosquito-borne disease risks during the summer.

Walleye recruitment success is less resilient to warming water temperatures in lakes with abundant largemouth bass populations

Lakes respond heterogeneously to climate, with implications for fisheries management. We analyzed walleye (Sander vitreus) recruitment to age-0 in 359 lakes in Wisconsin, USA, to (i) quantify the relationship between annual water temperature degree days (DD) and walleye recruitment success and (ii) identify the influence of lake characteristics — area, conductivity, largemouth bass (Micropterus salmoides) catch rates, and mean DD — on this relationship. The relationship between walleye recruitment and annual DD varied among lakes and was not distinguishable from zero overall (posterior mean = −0.11, 90% CI = −0.34, 0.15). DD effects on recruitment were negative in 198 lakes (55%) and positive in 161 (45%). The effect of annual DD was most negative in lakes with high largemouth bass densities, and, on average, the probability of recruitment was highest in large lakes with low largemouth bass densities. Conductivity and mean DD influenced neither recruitment nor the effect of annual DD. Walleye recruitment was most resilient to warming in lakes with few largemouth bass, suggesting that the effects of climate change depend on lake-specific food-web and habitat contexts.

Seasonal Reproductive Biology of Drosophila suzukii (Diptera: Drosophilidae) in Temperate Climates.

Drosophila suzukii (Matsumura; Diptera: Drosophilidae) is a key pest of sweet cherry and small fruits worldwide. The present studies were designed to describe the reproductive physiology in both sexes, through dissections of their reproductive organs. We extensively dissected female D. suzukii throughout the season from 2013 to 2016 and classified the reproductive status flies based on five recognizable ovarian maturation stages: 1) no ovaries; 2) unripe ovaries 3) ripening eggs in ovarioles; 4) mature eggs in ovarioles; and 5) mature eggs in the abdomen. Development was examined as a function of calendar days as well as degree-days (DD). Results obtained from winter collections revealed that females collected from November to March contained a lower percentage of mature eggs than females collected from April to September. These data suggest that environmental conditions during the dormant period induce reproductive diapause. Oogenesis likely increased with an increase in mean monthly temperatures and DD. The first overwintered females with mature eggs were dissected as early as 21 February 2014 in Trento (7 DD). Additionally, we found that a low proportion of males (less than 50%) had sperm in their testes between January and March, yet during the same period females already have sperm stored in their spermathecal. Ivy berries was an alternative but unfavorable non-crop host during the late dormant period, as evidenced by emergence of smaller adults when compared to individuals emerging from cherry fruits. This study showed that D. suzukii females have great potential for oviposition early in the season, posing a risk to early season maturing crop hosts.

The Impact of Weather Conditions on Culex pipiens and Culex restuans (Diptera: Culicidae) Abundance: A Case Study in Peel Region

Mosquito populations are sensitive to long-term variations in climate and short-term variations in weather. Mosquito abundance is a key determinant of outbreaks of mosquito-borne diseases, such as West Nile virus (WNV). In this work, the short-term impact of weather conditions (temperature and precipitation) on Culex pipiens L.-Culex restuans Theobald mosquito abundance in Peel Region, Ontario, Canada, was investigated using the 2002-2009 mosquito data collected from the WNV surveillance program managed by Ontario Ministry of Health and Long-Term Care and a gamma-generalized linear model. There was a clear association between weather conditions (temperature and precipitation) and mosquito abundance, which allowed the definition of threshold criteria for temperature and precipitation conditions for mosquito population growth. A predictive statistical model for mosquito population based on weather conditions was calibrated using real weather and mosquito surveillance data, and validated using a subset of surveillance data. Results showed that WNV vector abundance on any one day could be predicted with reasonable accuracy from relationships with mean degree-days >9 degrees C over the 11 preceding days, and precipitation 35 d previously. This finding provides optimism for the development of weather-generated forecasting for WNV risk that could be used in decision support systems for interventions such as mosquito control.

Disentangling the effects of area, energy and habitat heterogeneity on boreal forest bird species richness in protected areas

ABSTRACTAim One of the few general laws in ecology is that species richness is a positive function of area. However, it has been proposed that area would merely be a proxy for energy. Additionally, habitat heterogeneity has been found to be an important factor determining species richness. Yet the relative importance of those relationships is little known, and it is still unclear how they are brought about. We aimed to dissect which factors drive the species richness of boreal forest birds, and to identify the most probable mechanisms.Location Forested protected areas in Finland.Methods Using bird line census data collected in 104 protected areas, we ran simultaneous autoregressive models to explain the species richness of forest birds. We explored the value of forest area, tree volume, tree growth, mean degree days and habitat heterogeneity as explanatory variables and used the species richness within different species groups, based on the predictions of hypothesized mechanisms, as a response variable.Results Energy, rather than area or habitat heterogeneity, seems to be the main driver of species richness in boreal forest birds. More specifically, productive energy was a better predictor of total species richness than solar energy. Among the tested hypothetical mechanisms, the sampling hypothesis received strong support. After accounting for sampling, solar energy had an effect on species richness.Main conclusions As productive energy, such as tree volume, is associated with species richness, high‐energy areas should be prioritized in forest conservation planning. Reductions in productive energy may first lead to the disappearance of the rarest species due to the random sampling process. Climate change may result in increased species richness due to increasing amount of productive and solar energy in forests. However, the range shifts of bird species may not be fast enough to keep up with the temperature increases.

Forecasting Sclerotinia Disease on Lettuce: Toward Developing a Prediction Model for Carpogenic Germination of Sclerotia

ABSTRACT The feasibility of developing a forecasting system for carpogenic germination of Sclerotinia sclerotiorum sclerotia was investigated in the laboratory by determining key relationships among temperature, soil water potential, and carpogenic germination for sclerotia of two S. sclerotiorum isolates. Germination of multiple burials of sclerotia to produce apothecia also was assessed in the field with concurrent recording of environmental data to examine patterns of germination under different fluctuating conditions. Carpogenic germination of sclerotia occurred between 5 and 25 degrees C but only for soil water potentials of >/=-100 kPa for both S. sclerotiorum isolates. Little or no germination occurred at 26 or 29 degrees C. At optimum temperatures of 15 to 20 degrees C, sclerotia buried in soil and placed in illuminated growth cabinets produced stipes after 20 to 27 days and apothecia after 27 to 34 days. Temperature, therefore, had a significant effect on both the rate of germination of sclerotia and the final number germinated. Rate of germination was correlated positively with temperature and final number of sclerotia germinated was related to temperature according to a probit model. Thermal time analysis of field data with constraints for temperature and water potential showed that the mean degree days to 10% germination of sclerotia in 2000 and 2001 was 285 and 279, respecttively, and generally was a good predictor of the observed appearance of apothecia. Neither thermal time nor relationships established in the laboratory could account for a decline in final percentage of germination for sclerotia buried from mid-May compared with earlier burials. Exposure to high temperatures may explain this effect. This, and other factors, require investigation before relationships derived in the laboratory or thermal time can be incorporated into a forecasting system for carpogenic germination.

Effects of stripping time on the success of the artificial incubation of white‐clawed crayfish, Austropotamobius pallipes (Lereboullet), eggs

One of the main limiting factors in the use of artificial incubation techniques on crayfish farms has been the widespread belief that eggs should be stripped from females in the late stages of embryogenesis. In order to disprove this idea, three different times for egg removal were tested in white-clawed crayfish, Austropotamobius pallipes (Lereboullet): (1) just before the gastrulation process (mean degree days= 335, 34 days after spawning); (2) when the embryo was between the closing of the blastopore and the appearance of mandibular rudiments (mean degree days= 524, 56 days after spawning); and (3) when the embryo had thoracic appendage rudiments (mean degree days= 810, 92 days after spawning). The results showed that it is possible to attain acceptable survival rates up to juvenile stage 2 (51%), even when eggs have been detached at the earliest time (34 days after spawning), in such a way that artificial incubation is used for more than three-quarters (75.7%) of the total duration of the embryonic development. Factors such as the incubation device, water quality and incubation conditions have a major influence on the success of the process. Finally, a critical period was observed during the last stages of development in the present study, particularly between the eyed stage and juvenile stage 2, with mortality rates of between 26.7% and 56%.

Artificial incubation of crayfish eggs ( Pacifastacus leniusculus Dana) from early stages of embryonic development

Three experiments on artificial incubation of crayfish eggs ( Pacifastacus leniusculus Dana) were carried out under different thermal regimes using a specially designed incubator tested in previous trials. Each treatment included a period of low temperature of different duration. Three flow rates were used in each experiment: 3.0, 1.5 and 0.5 l/min. In all cases the eggs were detached from females at three phases of embryonic development: beginning of gastrulation (mean degree days 230, 18 days after spawning); embryo between closing of the blastopore and appearance of mandibular rudiments (mean degree days 365); and embryo with naupliar appendages (mean degree days 480). The results showed that it is possible to auain acceptable juvenile stage 2 survival rates (58.9%) even though eggs were detached at the earliest embryonic phase (beginning of gastrulation). In the experimental incubator, flow rates could be reduced to 0.5 l/min without decreasing survival. The highest survival to juvenile stage 2 (72.1%) was obtained by delaying egg removal until the appearance of naupliar appendages, and using a thermal treatment of 15.5 ° ± 1 °C preceded by a 3-week period of low temperature (5 ° ± 1 °C) commencing at stripping time.

Threshold Temperature and Degree-day Estimates for Development of Immature Southern Pine Coneworms (Lepidoptera: Pyralidae) at Constant and Fluctuating Temperatures

First- and fourth-instar Dioryctria amatella (Hulst) were reared on an artificial diet at six constant temperatures in the laboratory and outdoors. Threshold temperature for larval development was 13°C, and development from newly hatched larva to pupa and larva to adult required 303 and 493 degree-days (DD), respectively. Mean DD for development of immatures in a shaded area outdoors during spring and early summer of 1984 varied only 8 DD from estimates derived from constant-temperature data. Threshold temperature did not vary with larval age.

Induced ovulation in coho salmon ( Oncorhynchus kisutch). I. Further studies on the use of salmon pituitary preparations

The work presented extends previous studies on the use of pituitary preparations to induce ovulation in coho salmon. It has been demonstrated that coho salmon may be successfully induced to ovulate up to 2 months prior to their normal peak spawning period and that the use of a single injection of salmon pituitary extract (SPE) to induce ovulation is possible. In November 1977, the experimental fish were divided into six groups. Three groups were administered injections of 0.1 mg/kg partially purified salmon gonadotropin (SG-G100) followed 3 days later by either 2.0 mg/kg SG-G100, 25.0 SPE or 50.0 SPE. A fourth group was administered 10.0 mg/kg SPE followed 3 days later by 50.0 mg/kg. The fifth group received a single injection of 100.0 mg/kg SPE. A control group was injected with saline. All treated groups ovulated significantly earlier than the control. Egg survival and mean egg diameter were within the normal range for coho from Big Qualicum. In September and October 1978, the 10.0 mg/kg SPE primer followed by a 50.0 mg/kg secondary SPE injection were compared to a saline control. In addition, in September a second test group was administered the same primer but was followed by three daily 25.0 mg/kg SPE injections. All treatment groups ovulated significantly earlier than their controls. However, only the 10–50 SPE treatment groups reached cumulative ovulation levels comparable to the controls. Further, these levels increased with closer proximity to the normal spawning period from approximately 40.0% in September to approximately 80% in October. Egg survival and mean degree days to the eyed stage and to hatching for the October experiment fell within the normal range for the Big Qualicum stock. In November 1978, four groups of seven fish received single intraperitoneal or intramuscular injections of either 33.0 mg/kg or 66.0 mg/kg SPE. A control group was injected with saline. All groups ovulated significantly earlier than the control. No significant differences were found between test groups related to dosage level or route of injection. Egg survival and mean degree days to the eyed stage and to hatching fell within the normal range for this stock.

NORMAL DEGREE DAYS BELOW ANY BASE*

Abstract Heating engineers sometimes have need for normal degree days for bases other than 65° F. Further analysis of the relationship between mean temperature and mean degree days for base 65° F. showed that the form of this relationship is independent of the base. This makes it possible to vary the base to any value and hence to compute degree-day normals for any base from normal temperature. Results are presented for selected stations for bases ranging from 35° to 70° F.

THE RATIONAL RELATIONSHIP BETWEEN HEATING DEGREE DAYS AND TEMPERATURE1

The probability function of degree days below the base 65° F. is derived from the temperature probability function. Standard statistical analysis is applied to this function to obtain the relationship between mean degree days and mean temperature. This relationship is modified for use with available data and applied in the conversion of a monthly normal temperature for Detroit to the corresponding degree day normal.