Transcript Temperature dependent development, cold tolerance and

Temperature dependent development, cold tolerance, predicted numbers of
generations/year and predicted areas of establishment
Methods – temperature dependent
development
• insects reared from egg to adult at 16, 20.5,
25.5, 29, 33, 34, and 36oC at 14:10, 60-70% RH
• recorded days to molting
• analyses:
– linear regression to calculate degree day requirement
and lower development threshold.
– non-linear regression to estimate upper lethal
threshold
– use of historical weather data to map predicted
numbers of generations/year across North America
Results
Temperature oC
Stage
16.0
20.5
25.5
29.0
33.0
34.0
36.0
Egg
13.5
10.2
5.2
5.0
3.4
5.0
-
L1
3.8
3.1
8.2
1.9
2.4
3.4
-
L2
5.9
4.5
2.8
2.0
2.5
2.4
-
L3
17.3
6.2
4.1
1.8
1.7
3.4
-
L4
-
3.2
3.7
2.5
1.6
2.2
-
L5
-
8.3
4.8
4.9
2.1
2.8
-
Pupae
-
12.4
6.1
5.1
4.1
5.0
-
47.9
29.8
23.1
17.8
19.2
Egg to Pupae
Effect of temperature on survival
100
% Mortality
80
60
40
20
0
14
16
18
20
22
24
26
28
Temperature ( 0C)
30
32
34
36
38
Developmental rate (1/D)
Linear model
0.06
Observed
0.05
Predicted
0.04
0.03
0.02
0.01
DD = 1/slope = 355
0
10
15
13.4
20
25
Temperature
30
35
40
Non-linear model
0.07
Developmental Rate (Days
0.06
All immature
0.05
0.04
0.03
0.02
0.01
0.00
15
20
25
30
35
o
Temperature ( C)
34.8
Predicted number of generations/year
But.........
• Map prediction assumes continual development
throughout the year as long as temperatures are above
the lower threshold
• We know that this is not true due to reproductive
diapause during the winter
• Based on sampling data in Saint Lucie Co., we believe
that diapause is initiated by mid November and ends in
mid April. During this period, about 796 DD are
accumulated.
• Thus, the map overestimates the number of
generations/year in St. Lucie Co. Florida by about 2.2
(796/355).
Methods – cold tolerance
• young adults held at 0, 5, and 10oC for
0.5, 1, 2, 4, and 8 days.
• after chilling period, adults placed at room
temperature and status (alive/dead)
assessed after 24 hours
Results – cold tolerance
Temperature
(oC)
Ltime50
Ltime90
10
N/A
N/A
5
5.14
12.61
0
3.75
9.84
Percentage survival (%)
100
0oC
80
60
40
20
0
0
1
2
3
4
5
Days
6
7
8
9
10
Ltime90 ≥ 10 days at 0oC
Ltime50 ≥ 4 days at 0oC
Limitation of prediction:
- we used summer insects
- diapause insects may be
more cold tolerant