Alfalfa Leafcutting bees
Fahrenheit
Celsius
Pteromalus
venustus
Fahrenheit
Celsius
Lygus bug
Fahrenheit
Celsius
Alfalfa
Fahrenheit
Celsius
A Degree Day Primer
Degree-day concepts
Developmental thresholds
Degree-days
Accumulated degree-days
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*(Degrees Fahrenheit)*
 | Lower threshold: 60o F |
| Degree day accumulations required for
50% adult emergence: 493-560 DD F (at 85o F: 85-60=25 degree days
per day, or 21-22 days) |
| If bees must be cooled below 85o F, you can calculate manually how many
degree days have accumulated at the lower temperature. Open a few cells to see what
is the average condition of the pupae, and use the table below to calculate how many more
degree days are required: |
Pupal Stage
|
Degree Days to 50% emergence |
Days to 50% emergence
at 84o F |
| All white, recently molted |
264 |
11 |
| Eyes light pink to tan |
234 |
10 |
| Eyes dark red or brown |
189 |
8 |
| blackening pupa, body darkening |
108 |
4-5 |
| Black pupa, entire body pigmented |
72 |
3 |
For example, if the average stage of a sample of bees is dark-eyed, then an additional 8
days are required at 84o F for 50% emergence. If the incubator is held at
75o F for three days, and then brought up to 85o F, it will be
75-60=15 degree days per day for the three days at 75o F = 45 Degree
days. That leaves 189-45=144 degree days to go, or 5.8 days at 85o F.
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| Lower threshold: 59o F |
| Degree day accumulations required for
5% adult emergence: 182-272 |
| Degree day accumulations required for
50% adult emergence: ~292
|
- Question: Can you calculate how many
days it
would take for 50% parasite emergence at an incubator temperature of 85o F?
Consider that each day will be 85-59=26 degree days.
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| Lower threshold: 52o F |
| Degree day accumulations required for
50% egg hatch: 250o |
| Generation time, egg to adult:
623 degree days.
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|
Lower threshold: 41o
F |
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Degree day accumulations for bloom:
~1000-1600 ??? |
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*(Degrees Celsius)*
| Lower threshold: 15.5o C |
| Degree day accumulations required for
50% adult emergence: 274 - 311DD C
(at 30o C: 30-15.5=14.5 degree days per day, or 19-20 days) |
| If bees must be cooled below 30o C, you can calculate manually how many
degree days have accumulated at the lower temperature. Open a few cells to see what
is the average condition of the pupae, and use the table below to calculate how many more
degree days are required: |
Pupal Stage
|
Degree Days to 50% emergence |
Days to 50% emergence
at 29oC |
| All white, recently molted |
147 |
11 |
| Eyes light pink to tan |
130 |
10 |
| Eyes dark red or brown |
105 |
8 |
| Blackening pupa, body darkening |
60 |
4-5 |
| Black pupa, entire body pigmented |
40 |
3 |
For example, if the average stage of a sample of bees is dark-eyed, then an additional 8
days are required at 29o C for 50% emergence. If the incubator is held at
20o C for three days, and then brought up to 30o C, it will be
20-15.5=4.5 degree days per day for the three days at 20o C = 13.5 Degree
days. That leaves 105-13.5 =91.5 degree days to go, or 6.3 days at 30o C.
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| Lower threshold: 15o C. |
| Degree day accumulations required for 5% adult emergence:
105-151.5 |
| Degree day accumulations required for
50% adult emergence: ~162
|
- Question: Can you calculate how many days it
would take for 50% parasite emergence at an incubator temperature of 30o C?
Consider that each day will be 30-15=15 degree days.
-
| Lower threshold: 11o C |
| Degree day accumulations required for
50% egg hatch: 140o |
| Generation time, egg to adult:
346 degree days.
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Lower threshold: 5o
C |
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Degree day accumulations for
bloom: ~555-890???
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From University of California Statewide Integrated Pest Management Project
Temperature controls the developmental rate of many organisms. Plants and invertebrate
animals, including insects and nematodes, require a certain amount of heat to develop from
one point in their life cycles to another. This measure of accumulated heat is known as
physiological time. Theoretically, physiological time provides a common reference for the
development of organisms. The amount of heat required to complete a given organism's
development does not vary - the combination of temperature (between thresholds) and time
will always be the same. Physiological time is often expressed and approximated in units
called degree-days (oD).
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- Upper and lower developmental thresholds have been determined for some organisms through
carefully controlled laboratory and field experiments. For example, the lower
developmental threshold is 51° F and the upper developmental threshold is 90° F for the
San Jose scale (Quadraspidiotus perniciosus). Thresholds vary with different
organisms.
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The lower developmental threshold for an organism is the temperature below which
development stops. The lower threshold is determined by the organism's physiology.
- The total amount of heat required above the lower threshold for an organism to develop
from one point to another in its life cycle is calculated in units called degree-days
(°D). Sometimes called heat units, degree-days are the accumulated product of time and
temperature between the developmental thresholds for each day. One degree-day is one day
(24 hours) with the temperature above the lower developmental threshold by one degree. For
instance, if the lower developmental threshold for an organism is 51° F and the
temperature remains 52° F (or 1° above the lower developmental threshold) for 24 hours,
one degree-day is accumulated.
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- Each developmental stage of an organism has its own total heat requirement. Development
can be estimated by accumulating degree-days above the temperature threshold throughout
the season. Each species requires a defined number of degree-days to complete its
development. The accumulated degree-days from a starting point can help predict when a
developmental stage will be reached. The date to begin accumulating degree-days, known as
the biofix date, varies with the species. Biofix dates are usually based on specific
biological events such as planting dates, first trap catch, or first occurrence of a pest.
Accumulation of degree-days should be done regularly, especially when a control action
decision is near.
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