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

Heat Requirements for the Development of the Black cutworm, Agrotis ipsilon 119
temperature increased. The means of incubation periods were 6.18, 3.67 and 2.81
days at 20, 25 and 302C, respectively. Statistically, there are obvious significant
differences in A. ipsilon incubation period at all the tested constant temperatures.
Table (1): Development of A. ipsilon eggs under different constant temperatures and its thermal requirements.
Temp.
( °C)
Incubation
period
(days ± S.E) Expect
duration (days)
Rate of
development
%
Expect rate of
development
%
20 6.18 ± 0.04 a 6.02 16.18 16.61
to
(˚C)
Degree days
(dd΄s)
25 3.67 ± 0.18 b 3.79 27.24 26.37 11.49 49.6
30 2.81 ± 0.02 c 2.77 35.71 36.14 51.8
Average 51.3
L.S.D 0.16
The threshold of egg development was calculated and illustrated in Fig. (1);
it was found to be 11.49C. The average of thermal units in degree – days required
for the completion of development of this stage was 51.3 dd's. The three observed
values of eggs rate of development at the constant temperature range (20 - 30C)
gave a remarkable good fit to the calculated temperature – velocity line having the
formula Y = 1.95 x - 22.4 (Fig. 1).
R a t e o f d e v(1/t e l ox1 p0 ) m0 e n t
4 0
3 5
3 0
2 5
2 0
1 5
1 0
5
0
r = 0 . 9 9 K = 5 1 . 3
y = 1 . 9 x5 - 2 2 . 4
0 5 1 0 1 5 2 0 2 5 3 0
T e m p e r a t u r e ( ° C)
F i g . ( 1 ) : 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 e g g s a n d d i f f e r e n t
Fig. (1): The regression line of the relation c o nbetween s t a n t t e mthe p e rate r a t u rof e s development .
of A. ipsilon eggs and
different constant temperatures.
Larval stage:
Table (2) indicated that the average larval duration varied from 33.06 days
at 20C to 15.81 days at 30C. The analysis of variance showed significant
differences (P < 0.01) between the means of larval duration at all tested
temperatures. The lower threshold of development (t 0) for the larval stage was
10.63C as indicated in Fig. (2).
The same Table showed that the average thermal units required for larval
developmental till pupation was 303.5 dd's as determined by the thermal
summation equation.
52.6