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Psyche 14:80-86, 1907.

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ow YSYCHIS [August
MIXOGASTEE BREVIVENTRIS Kahl.
M. breviventris Kahl, Kansas Univ. Quart., VI, p. 137, 1897. A male and female of this interesting species were collected by Mr. Erich Daecke, at Lucaston, N. J., August 27, 1905.
The type, a female, was described from Law- rence, Kans. The male differs but little from the female except that the fourth segment is nearly twice the length of the third, the posterior border on both being greatly dilated towards the lateral margins; the fifth segment and hypopygium (in the specimen before me) seem to be injured or forced within the abdomen, so that they cannot be accurately described.
TRICHOGRAMMA PRE TIOSA RILEY: SEASONAL HISTORY. BY A. A. GIRAULT, WASHINGTON, D. C.
TEE paper here presented for publication is one of a series on this insect based on observations and studies made during the Cotton Bollworm Investigations in Texas in 1904, by the U. S. Department of Agriculture. The observations were made in the laboratory at Paris, latitude 33O, 45' north and the host of the parasite was Helio- this obsoleta Fabricius, unless otherwise stated in the text. In their report on the bollworm, Quaintance and Brues (1905) have already given the substance of much that is to follow, but I believe the observations of enough importance to justify elabora- tion, an impossibility in connection with an economic report of that kind. The species under consideration is a remarkable example of an hymenopterous insect having multiple generations, and to this fact may be largely attributed its efficiency as a parasite. From the beginning to the end of the breeding season of 1904, it was under constant observation, and in the laboratory many successive generations were bred, so that actual records were obtained for fifteen consecutive cycles from the latter part of May to the first week in November. In addition to this direct evidence, there was also obtained much supplementary data, which war- rants a positive statement to the effect that there were at least eighteen distinct gener- ations of the little egg-parasite in the vicinity of Paris in 1904. The records show that the parasites began to appear about May 3rd, corresponding to the first noticeable Pnrhe 14330.86 (1937). hup //psyche cntclub org/14/14-080 html



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19071 GIRAULT-TRICHOGRAMMA PRETIOSA RILEY 81 appearance of the host eggs on corn, and they were present throughout the season in increasing numbers until about November 20th. To obviate further unnecessary discussion and for the sake of clearness and convenience, the generations are tabulated as follows:
Table I.
Generations at Paris. Texas. 1904.
Generat ion
No.
1.
2.
3.
4.
5.
6.
7.
8.
9 :
10.
11.
12.
13.
14. .
15.
16.
17.
18.
18a.
18b.
18c.
Eggs
deposited.
May 3
May 16
May 26
June 4
June 14
June 22
July 1
July 11
July 20
July 29
August 6
August 14
August 25
September 2
September 11
September 21
October 1
October 14
October 14
October 14
October 14
Sums
Averages
Adults out.
May 16
May 26
June 6
June 14
June 22
July 1
July 9
July 20
July 28
August 6
August 14
August 23
September 2
September 11
September 20
September 30
October 14
November 2
November 7
November 8
November 10
Approximate 1engt.h
of cycle.
13 days.
10 '(
11 '(
10 <'
8 ('
9 ('
8 "
9 "
8 '(
8 "
8 "
9 '(
8 "
9 "
9 "
9 "
13 '(
19 ('
24 ''
25 "
27 "
. 254 days.
. 12 days. .
Sums of
effective temperature.
324.1å Fahr.
313.2
354.7
318.4
297.2
330.9
298.9
365.7
300.
298.7
298.4
364.0
308.4
308.
314.2
323.1
408.1
365.0
449.
465.
480.
7285.0
346.6' Fahr.
By consulting table I, it is seen that the developmental period of a generation



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0.4 PSYCHE [August
varied considerably, from about 8 to 27 days, according to the season. Upon the
approach of warm weather, it gradually decreased and remained practically constant from about the middle of June to about the middle of September, or during the warm summer months. In the fall, it rapidly increased in length, becoming twice as long in November as it was for the first generation in May, as would be expected from the fact that the mean daily effective temperature at that time of the year was very low. Table I1 is introduced to show as accurately as possible the lengths of the life cycles at different dates in 1904.
Table II.
Lengths of the Life Cycle, Paris, Texas, 1904. Lot No.
Dates.
May 3-May 16
May26-June6
May 27-June 7
June 1- June 12
June &June 14 ,
June14ÌÔJune2
June 14ÌÔJun 22
June20-June28
June 22-June 30
June 22-July 1
July 1-July 9
July 20-July 28
July 29-August 6
Sept. 12-Sept. 20
Sept. 21-Sept. 30
Sept. 26-Oct. 4
Sept. 28-Oct. 6
Oct. 1-Oct. 14
Oct. 14-Nov. 2
Oct. 14-Nov. 7
Oct. 14-Nov. 8
Oct. 14-Nov. 10
Eggs deposited.
May 3
P. M. May 26
P. M. May 27
A. M. June 1
P. M., June 4
A. M., June 14
A. M., June 14
A. M., June 20
Noon, June 22
P. M., June 22
A. M., July 1
P. M., July 20
Noon, July 29
P. M., Sept. 12
A. M., Sept. 21
A. M., Sept. 26
A. M., Sept. 28
Noon, Oct. 1
A. M., Oct. 14
A. M., Oct. 14
Oct. 14
P. M., Oct. 14
Adults out.
May 16
Noon, June 6
A. M. June 7
A. M., June 12
Noon, June 14
A. M., June 22
A. M., June 22
P. M., June 28
Noon, June 30
A. M., July 1
A. M., July 9
A. M., July 28
A. M., August (
P. M., Sept. 20
A. M., Sept. 30
A. M., Oct. 4
P. M., Oct. 6
Noon, Oct. 14
A. M., Nov. 2
P. M., Nov. 7
Nov. 8
P. M., Nov. 10
Approximate length
of cycle.
Days.
Hours.




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Table III.
Hibernation Statistics, Oct. 11-20, J904. late tagged
and known
parasitized.
Hosts not ex-
luding pamsitei
by Nov. 20.
Host,
Lot No.
Total
hibernating.
hosts. Location.
I
Condition when last exam-
ined (Nov. 20.)
Hosts excluding par-
asites and date.
October 11
12
14
14
14
14
14
17
17
19
19
Cotton leaves
Dead corn leaves
Dead corn leaves
Cotton leaves
Corn leaves
Corn leaves
Corn leaves
Corn leaves
Young corn
Young corn
Corn
2 - Oct. 19
0
1 - Oct. 18
3 - Oct. 21
3 - NOV. 2-6
11 - NOV. 2-15
5 - NOV. 7-10
8 - Oct. 20-NOV, 4
2 - NOV. 6
0
3 - Oct. 23-NOV. 4
Healthy.
Healthy.
it
On ground; healthy.
On ground.
Healthy.
Totals
8 - Oct. 18-Nov. 151 15 1 15 ' IFoliage wilted and dead. Planted for experimental purposes.
2 28.3 per cent.
Table IV. Hibernation Statistics, Oct. 21-Nov. 3, 1904. Date tagped
and known
parasitized.
Hosts not ex-
luding parasites
by Nov. 20.
Host
Lot No.
Total
hibernating.
No.
l0StS.
Condition when last exam-
ined (Nov. 20).
Hosts excluding par-
asites and date.
Location.
Cotton leaves
i 1
it
it
(f
October 21
22
22
22
24
24
24
24
25
28
Nov. 1
3
1 - Oct. 23
1 - NOV. 15
10 - Oct. 29, Nov. 14
4 - NOV. 4-7
0
1 - NOV. 6
0
0
0
0
2 - NOV. 16
0
Healthy
6 healthy; 1 washed off.
Healthy.
it
11 healthy; 3 washed off
Healthy; 7 on ground.
On ground
Healthy.
t i
it
it
a
-
Young corn
it
Cotton leaves
ii
it
it
t i
Totals
-
1 Planted for experimental purposes.
78.4 per cent.
Summary of Tables 111 and IV.




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1907,1 GIRA ULT-TRICHOGRAMMA PRETIOSA RILEY 85 The tables serve to make clear the fact that at least as early as October 12th, hibernation had commenced, but that by October 20th only 28.3 percent were in that state, the remaining eventually emerging as adults. After October 20th, how- ever, table IV shows that nearly 80 per cent of the parasites had not emerged up to the time of killing frosts (Nov. 20th and a few days earlier), or were hibernating. The data is not as conclusive as desirable, for it may be urged that the observations were not continued late enough to state definitely whether or not the adults issued after November 20th, and then hibernated. But as evidence against this, I offer the fact that adults failed to issue from 10 of these tagged hosts up to the middle of December, they having been carried to Washington, D. C., in vials and confined in the laboratory.
Another fact indicating hibernation as a larva in the host, is that no material increase in length of life could be noticed in the adults in the late part of October and in November. In reality, they seemed to perish more easily at that time than in the summer. During the observations, most of the adults issued during warm spells. Assuming that the average number of eggs deposited by a female is 30, a con- servative estimate, and that at least half of these will produce other females, the progeny of a single pair for such a season as 1904 in Texas would total to the un- thinkable number of 3,031,721,260,073, 800,781,250, as shown in the accompany- ing table by generations.




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86
Generation
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
PSYCHE
[August
Table V. Progeny of a Single Pair, by Generations. No. of descendants. Remarks.
30 Descendants of hibernating female.
450
6750
101,250
1,518,750
22,781,250
341,718,750
5,125, 781, 250
76,886,718,750
1,153,300,781,250
17,299,511,718,750
259,492,675,781,250
3,892,390,136,718,750
59, 885, 852,050, 781, 250
898,287,780,761,718, 750
13,474,316,711,425,781,250
202, 114,750,671,386,718,750
3,031, 721, 260,073, 800, 781,250
All of this, of course, is purely speculation, for we have no means of actually obtaining vital statistics of this kind. No allowances have been made for mortality in the reproducing females, or in the young, and in order to make the calculation as conservative as possible, the totals should probably be halved, on the theory that but half of the female descendants in any one generation survive to reproduce. This would still leave us in a maze of unthinkable totals. The figures are merely intro- duced to show the possibilities in rapid reproduction present in this important egg- parasite, and no claim is made that they represent anything like actual fact. LITERATURE REFERRED TO.
1892.
Howard, 'Leland Ossian.
Proc. U. S. Nat. Museum, Washington, XIV (1891), p. 577.
1905. Quaintance, Altus Lacy and Charles Thomas Brues. The Cotton Boll- worm. Bull. No. 50, Bureau Ent., U. S. Dep. Agric., Washington, p. 117. 1906. Froggatt, Walter. Agric. Gazette New South Wales, Sydney, XVII, pp. 390-391.