Temperature Degree Days Research Articles

Ontogenetic Behavior and Migration of Chinese Sturgeon, Acipenser sinensis

The Chinese sturgeon, Acipenser sinensis, is an anadromous protected species that presently only spawns in the Yangtze River. Using laboratory experiments, we examined the behavioral preference of young Chinese sturgeon to physical habitat (water depth, illumination intensity, substrate color, and cover) and monitored their downstream migration. Hatchling free embryos were photopositive, preferred open habitat, and immediately upon hatching, swam far above the bottom using swim-up and drift. Downstream migration peaked on days 0-1, decreased about 50% or more during days 2-7, and ceased by day 8. Days 0-1 migrants were active both day and night, but days 2-7 migrants were most active during the day. After ceasing migration, days 8-11 embryos were photonegative, preferred dark substrate and sought cover. Free embryos developed into larvae and began feeding on day 12, when another shift in behavior occurred-larvae returned to photopositive behavior and preferred white substrate. The selective factor favoring migration of free embryos upon hatching and swimming far above the bottom may be avoidance of benthic predatory fishes. Free embryos, which must rely on yolk energy for activity and growth, only used 19 cumulative temperature degree-days for peak migration compared to 234 degree-days for growth to first feeding larvae, a 1 : 12 ratio of cumulative temperature units. This ratio suggests that sturgeon species with large migratory embryos, like Chinese sturgeon, which require a high level of energy to swim during migration, may migrate only a short time to conserve most yolk energy for growth.

Temperature Dependent Models To Predict Regional Differences in Corn Rootworm (Coleoptera: Chrysomelidae) Phenology

Western corn rootworms, Diabrotica virgifera virgifera LeConte, only recently have become a serious corn pest in New York and other states in the Northeast. Because soil conditions, topography, and climate differ from the Midwest corn belt, questions arose as to the validity of previously published phenology models. Our study evaluated larval occurrence and adult emergence of western and northern corn rootworm, D. barberi Smith & Lawrence, in 11 fields in central New York during 1991 (2 fields), 1992 (3 fields), and 1993 (6 fields). Logistic regression models predicted cumulative occurrence/emergence from Julian date or degree-day accumulations calculated from either soil (base 11°C) or air temperatures. Air temperature degree-days were calculated for minimum thresholds ranging from 1-16°C. Additional accumulations were determined by varying the maximum developmental threshold from 1°C above the lower threshold to 30°C. Minimum thresholds in the latter series of calculations were set equal to 4, 6, 9, and 11°C. Julian date was a relatively poor predictor of all immature and adult stages. However, accuracy of air temperature models was dependent on choice of thresholds. The best fitting air temperature models either used minimum developmental thresholds near 6°C for immature stages and 1-2°C for adult emergence or calculated degree-days using a minimum threshold of 11°C and a maximum threshold of 18°C. Both soil and air temperature models indicated regional differences in immature development and adult emergence. Although site-specific models gave the best prediction of western corn rootworm adult emergence, adult emergence at New York and Illinois sites could be predicted by adjusting daily air temperature degree-days by the expected accumulations from 1 January to 30 September.

Heat Retention During Incubation in Nests of the Alfalfa Leafcutting Bee (Hymenoptera: Megachilidae)

Temperatures within polystyrene, paper, and wooden nests of the alfalfa leafcutting bee, Megachile rotundata (F.), were monitored during incubation at 30.0 °C. In the polystyrene and paper nests, temperatures began to increase 10 d after the start of incubation and continued to rise until adults emerged. Temperatures reached 35.1 °C In the polystyrene and 37.2 °C in the paper, while the wood nests never exceeded 30.6 °C. Compared with air temperature degree-days, cells in the center of the polystyrene nests accumulated up to 28 more degree-days after 20 d, whereas those in the paper accumulated 32 more degree-days. In polystyrene nests, heat units increased toward the center holes, reaching a maximum at the fifth row toward the center. Emergence was also monitored from polystyrene blocks, wooden boards, and loose cells. Females emerged 2.1 d later from polystyrene blocks compared with wooden boards and the emergence period was lengthened by 2.5 d. Because of the increased temperatures and the prolonged emergence period experienced with these materials, we recommend that filled polystyrene and paper nests not be incubated but be stripped of their cocoons as they were designed.

Seasonal shoot growth of planted red pine predicted from air temperature degree days and soil water potential

On-site climatic measurements were used to model red pine ( Pinus resinosa Ait.) shoot elongation. Three study sites each consisting of three 0.2-ha plots were cleared and planted with red pine. Shoot growth was measured weekly for 2 years. Incremental seasonal growth of the leading shoot was estimated using a difference form of a modified Chapman-Richards growth function. Weekly growth was estimated as a function of air temperature degree days (4.4°C basis), soil water potential, and total expected seasonal growth. An example using the model compares varying site and climatic conditions and their effect on the pattern of seedling height growth during the growing season as well as their effect on the total amount of height growth realized at the end of the growing season.