methods – temperature dependent development
DESCRIPTION
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 36 o C at 14:10, 60-70% RH recorded days to molting - PowerPoint PPT PresentationTRANSCRIPT
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
ResultsTemperature 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 -
Egg to Pupae 47.9 29.8 23.1 17.8 19.2
0
20
40
60
80
100
14 16 18 20 22 24 26 28 30 32 34 36 38
Temperature (0C)
% M
orta
lity
Effect of temperature on survival
0
0.01
0.02
0.03
0.04
0.05
0.06
10 15 20 25 30 35 40
Temperature
De
ve
lop
me
nta
l ra
te (
1/D
)
Observed
Predicted
13.4
DD = 1/slope = 355
Linear model
All immature
Temperature (oC)
Dev
elop
men
tal R
ate
(Day
s
15 20 25 30 35
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
34.8
Non-linear model
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
Per
cent
age
surv
ival
(%
)
Days
0 1 2 3 4 5 6 7 8 9 10
0
20
40
60
80
100
0oC
Ltime90 ≥ 10 days at 0oC
Ltime50 ≥ 4 days at 0oC
Limitation of prediction: - we used summer insects - diapause insects may be more cold tolerant
