Heat Requirements for the Development of the Black cutworm ...

122
Hassan F. Dahi et al.
The three observed values for pre-oviposition rate of increase at rang of
temperature from 20 to 30C, gave also a remarkable good fit to the calculated
temperature – velocity line having the formula Y = 2.619 x - 28.96 (Fig.4).
Fig. ( 4): The regression line of athe n d drelation i ffe r e n t c obetween n s t a n t t e mthe p e rrate a t u r eof s . development of A. ipsilon
pre-oviposition period and different constant temperatures.
The generation
The mean duration of generation at different constant temperature regimes
could be calculated using the total of mean duration of different developmental
stages (i.e. incubation period, larval stage, pupal stage and pre-oviposition period).
Theoretically, the results obtained from are method showed an approximate value
for mean duration of generation at different constant temperature regimes.
In the present study, the data in Table (5) indicate that the mean duration of
generation for A. ipsilon was 61.59, 38.96 and 29.73days at 20, 25 and 30 C,
respectively. Data revealed that the increasing of temperature accelerated the
developmental rate of A. ipsilon where it reached a maximum velocity at 30 C.
Table (5): Duration of A. ipsilon generation under different constant temperatures and its thermal
requirements.
Temp.
(°C)
R a te o f d e v e lo p(1/t m ex1 n t0
0)
Duration of
generation
(days ± S.E)
Expected
duration (days)
Rate of
increase
%
Expected
rate of
increase %
t o
(˚C)
Degree
Days
(DD΄s)
20 61.59 ± 1.37 a 60.97 1.62 1.64
583.3
25 38.96 ± 0.94 b 39.84 2.57 2.51 10.53 563.8
30 29.73 ± 0.66 c 29.58 3.36 3.38 578.8
Average 575.3
L.S.D 1.23
5 0
4 0
3 0
2 0
1 0
0
r = 0 . 9 9 K = 3 8 . 1
y = 2 .6 1 9 x - 2 8 .9 6
0 5 1 0 1 5 2 0 2 5 3 0 3 5
T e m p e ra t u re ( ° C)
F i g . ( 4 ) : T h e r e g r e s s i o n l i n e o f t h e r e l a t i o n b e t w e e n t h e
r a t e o f d e v e l o p m e n t o f A . i p s i l o n p r e - o v i p o s i t i o n p e r i o d
The lower threshold of development (t 0) could be estimated graphically
by extrapolation from Fig. (5), it was 10.53C and the average thermal summation
was 575.3 dd's.
These results agreed with the findings obtained by Kajanshikov (1946)
who found that the linear relationship between temperature and rate of development