Rearing immatures of Euschistus tristigmus tristigmus in 8L:16D, 8L: 4D:8L;4D, and 16L:8D showed that the length of each photophase, rather than an accumulated total of shorter photophases, during each 24 hr period was the determining factor in producing adult dimorphism in shoulder shape and number of midventral abdominal spots

McPherson, J. E

English

ValpoScholar

The Great Lakes Entomologist 
Volume 12 
Number 2 - Summer 1979 Number 2 - Summer 
1979 
Article 4 
June 1979 
Effects of Continuous and Split Developmental Photophases 
During Each 24 Hour Period on Adult Morphology in Euschistus 
Tristigmus Tristigmus (Hemiptera: Pentatomidae) 
J. E. McPherson 
Southern Illinois University 
Follow this and additional works at: https://scholar.valpo.edu/tgle 
 Part of the Entomology Commons 
Recommended Citation 
McPherson, J. E. 1979. "Effects of Continuous and Split Developmental Photophases During Each 24 
Hour Period on Adult Morphology in Euschistus Tristigmus Tristigmus (Hemiptera: Pentatomidae)," The 
Great Lakes Entomologist, vol 12 (2) 
Available at: https://scholar.valpo.edu/tgle/vol12/iss2/4 
This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. 
It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. 
For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 
1979 THE GREAT LAKES ENTOMOLOGIST 79 
EFFECTS OF CONTINUOUS AND SPLIT DEVELOPMENTAL 
PHOTOPHASES DLlRlNG EACH 24 HOUR PERIOD ON 
ADULT MORPHOLOGY IN EUSCHISTUS TRISTIGMUS TRlSTlGMUS 
(HEMIPTERA: PENTATOMIDAE)' 
ABSTRACT 
Rearing immatures of Euschistus tristigmus tristigmus in 8L:16D, 8L: 4D:8L;4D, and 
16L:8D showed that the length of each photophase, rather than an accumulated total of 
shorter photophases, during each 24 hr period was the determining factor in producing adult 
dimorphism in shoulder shape and number of midventral abdominal spots. 
Euschistus tristigmus occurs from northern Canada to southern Mexico (Van Duzee, 
1904) and contains two subspecies, luridus Dallas and tristigmus (Say) [= pyrrhocerus 
(Hemch-Schaeffer)]. E. t .  tristigmus is seasonally dimorphic (McPherson, 1975a). Adult 
dimorphism results from developmental photoperiod (McPherson, 1974; 1975b) with a 
threshold photoperiod of ca. 14.5L:9.5D (1ight:dark) involved in the dimorphic response 
(McPherson, 1979); animals reared in photophases above and below the threshold develop 
into pyrrhocerus (spinose shoulders, 0-2 midventral abdominal spots) and tristigmus (sub- 
triangular shoulders, 3-4 spots) form adults, respectively. 
All of the photoperiods used in the above experiments involved a 24 hr day and con- 
tinuous periods of light and dark (e.g., a 16 hr photophase followed by an 8 hr scotophase). 
Not determined previously was the necessity of these continuous periods for it was possible 
that the same results could be obtained by split photophases during each 24 hr period. The 
results of an experiment to determine this are presented here. 
MATERIALS AND METHODS 
Thirty males and 30 females from F3 generation laboratory stock were placed in an 
incubator (23.9 ? 1.1" C) under an 18L:6D photoperiod; the stock was established with 
individuals collected June-July, 1977, in Jackson County, in southern Illinois. They were 
maintained in mason jars (10 of each sexljar) provided with cheesecloth as an oviposition 
site, paper toweling strips and fdter paper, and fed green snap beans (Phaseolus vulgaris L.) 
as described by McPherson (1971). 
Each resulting egg cluster was placed in one of the following three photoperiods and the 
individuals reared to adult as described by McPherson (1971): 8L:16D, 8L:4D:8L:4D, and 
16L:8D. The 8L:4D:8L:4D photoperiod exposed the animals to only 8 hr of continuous light 
but a total of 16 hr of light124 hr. All individuals were reared at 23.9 + 1.1" C during the light 
and dark phases, and in about 130 ft-c during the light phases (Ken-Rad, 15W Daylight, 
F15T81D). 
Adult characters compared were shoulder shape (ratio of lengthlwidth) and number of 
midventral abdominal spots (McPherson, 1974). These characters had previously been 
shown to be dimorphic between adults reared in 8L: 16D and 16L:8D (McPherson, 1979), 
Shoulder ratios were compared with Duncan's multiple range test (Table l), and number of 
spots with Fisher's exact probability test (Table 2). The 0.01 level of significance was chosen 
for all comparisons. 
l~inancial support was provided by the Office of Research Development and Administration, Southern 
Illinois University, Carbondale Graduate School. Project No. 2-10631. 
Z~epartment of Zoology, Southern Illinois University, Carbondale, IL 62901. 
1
McPherson: Effects of Continuous and Split Developmental Photophases During
Published by ValpoScholar, 1979
80 THE GREAT LAKES ENTOMOLOGIST Vol. 12, No. 2 
Table 1. Comparison of shoulder shape (lengthlwidth) between E. t .  tristigrnus adults reared 
in continuous or split photophases during each 24 hr period. 
- - 
ShouldeP 
- Shouldera - Photoperiod Sex No. x Sex No. x 
aMeans followed by same letter within columns are not significantly different at the 0.01 level of probability 
by Duncan's multiple range test. 
Table 2. Comparison of number of midventral abdominal spots between E. t .  trisrigmus adults 
reared in continuous or split photophases during each 24 hr period. 
No. spots No. spots 
Photoperiod Sex 0-2 3-4 Pr0b.a Sex 0-2 3-4 P r ~ b . ~  
aFisher exact probability test. 
RESULTS AND DISCUSSION 
There was no significant difference in shoulder ratios between males or females reared in 
the 8L:16D and 8L:4D:8L:4D photoperiods; all had shoulder ratios less than 1.00 (subtrian- 
gular shoulder = tristigrnus form) (Table 1). Those reared in 16L:8D had shoulder ratios 
greater than 1.00 (spinose shoulder = pyrrhocerus form). There was also no significant 
difference in number of spots between males or females reared in the 8L:16D and 8L:4D: 
8L:4D photoperiods; most had 3-4 spots (= trisrigrnus form) (males, 90-95%; females. 95%) 
(Table 2). Those reared in 16L:8D generally had 0-2 spots (= pyrrhocerus form) (males, 
75%; females 80%). 
These results show that the length of the developmental photophase, rather than the total 
amount of light, during 24 hr determines the adult morph. They also help to explain the 
function of the dark period. 
In previous experiments it had been assumed that the observed dimorphism resulted from 
the length of the photophase, not the scotophase. For example, in the experiments to 
determine the threshold photoperiod (McPherson, 1979), animals were reared in photo- 
periods ranging from 8L: 16D to 18L:6D. It was possible that the range of scotophases, not 
photophases, determined the results. 
In the above experiment. scotophases of 16 and 4 hr were involved in the production of 
the tristigmus form and 8 hr, the pyrrhocerus form. Thus, it appears that photophase does 
determine the morph, that scotophase is functioning only to break the photophase, and that 
the length of the scotophase is unimportant between 16 and 4 hr, perhaps less. 
LITERATURE CITED 
McPherson, J. E. 1971. Laboratory rearing of Euschistus tristigmus tristigmus. J .  Econ. 
Entomol. 64:1339-1340. 
. 1974. Photoperiod effects in a southern Illinois population of the Euschistus 
tristigmus complex (Hemiptera: Pentatomidae). AM. Entomol. Soc. Amer. 67:943-952. 
2
The Great Lakes Entomologist, Vol. 12, No. 2 [1979], Art. 4
https://scholar.valpo.edu/tgle/vol12/iss2/4
1979 THE GREAT LAKES ENTOMOLOGIST 8 1 
. 1975a. Life history of Euschistus tristigmus tristigmus (Hemiptera: Penta- 
tomidae) with information on adult seasonal dimorphism. Ann. Entomol. Soc. Amer. 
68:333-334. 
. 1975b. Effects of developmental photoperiod on adult morphology in 
Euschistus tristigmus tristigmus (Say) (Hemiptera: Pentatomidae). Ann. Entomol. Soc. 
Amer. 68:1107-1110. 
. 1979. Effects of various photoperiods on morphology in Euschistus tristig- 
mus tristigmus (Hemiptera: Pentatomidae). Great Lakes Entomol. 1223-26. 
Van Duzee, E. P. 1904. Annotated list of the Pentatomidae recorded from America north of 
Mexico, with descriptions of some new species. Trans. Amer. Entomol. Soc. 30:l-80. 
3
McPherson: Effects of Continuous and Split Developmental Photophases During
Published by ValpoScholar, 1979


Effects of Continuous and Split Developmental Photophases During Each 24 Hour Period on Adult Morphology in \u3ci\u3eEuschistus Tristigmus Tristigmus\u3c/i\u3e (Hemiptera: Pentatomidae)

Valparaiso University

The Great Lakes Entomologist Volume 12 Number 2 - Summer 1979 Number 2 - Summer 1979 Article 4 June 1979 Effects of Continuous and Split Developmental Photophases During Each 24 Hour Period on Adult Morphology in Euschistus Tristigmus Tristigmus (Hemiptera: Pentatomidae) J. E. McPherson Southern Illinois University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation McPherson, J. E. 1979. "Effects of Continuous and Split Developmental Photophases During Each 24 Hour Period on Adult Morphology in Euschistus Tristigmus Tristigmus (Hemiptera: Pentatomidae)," The Great Lakes Entomologist, vol 12 (2) Available at: https://scholar.valpo.edu/tgle/vol12/iss2/4 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1979 THE GREAT LAKES ENTOMOLOGIST 79 EFFECTS OF CONTINUOUS AND SPLIT DEVELOPMENTAL PHOTOPHASES DLlRlNG EACH 24 HOUR PERIOD ON ADULT MORPHOLOGY IN EUSCHISTUS TRISTIGMUS TRlSTlGMUS (HEMIPTERA: PENTATOMIDAE)' ABSTRACT Rearing immatures of Euschistus tristigmus tristigmus in 8L:16D, 8L: 4D:8L;4D, and 16L:8D showed that the length of each photophase, rather than an accumulated total of shorter photophases, during each 24 hr period was the determining factor in producing adult dimorphism in shoulder shape and number of midventral abdominal spots. Euschistus tristigmus occurs from northern Canada to southern Mexico (Van Duzee, 1904) and contains two subspecies, luridus Dallas and tristigmus (Say) [= pyrrhocerus (Hemch-Schaeffer)]. E. t .  tristigmus is seasonally dimorphic (McPherson, 1975a). Adult dimorphism results from developmental photoperiod (McPherson, 1974; 1975b) with a threshold photoperiod of ca. 14.5L:9.5D (1ight:dark) involved in the dimorphic response (McPherson, 1979); animals reared in photophases above and below the threshold develop into pyrrhocerus (spinose shoulders, 0-2 midventral abdominal spots) and tristigmus (sub- triangular shoulders, 3-4 spots) form adults, respectively. All of the photoperiods used in the above experiments involved a 24 hr day and con- tinuous periods of light and dark (e.g., a 16 hr photophase followed by an 8 hr scotophase). Not determined previously was the necessity of these continuous periods for it was possible that the same results could be obtained by split photophases during each 24 hr period. The results of an experiment to determine this are presented here. MATERIALS AND METHODS Thirty males and 30 females from F3 generation laboratory stock were placed in an incubator (23.9 ? 1.1" C) under an 18L:6D photoperiod; the stock was established with individuals collected June-July, 1977, in Jackson County, in southern Illinois. They were maintained in mason jars (10 of each sexljar) provided with cheesecloth as an oviposition site, paper toweling strips and fdter paper, and fed green snap beans (Phaseolus vulgaris L.) as described by McPherson (1971). Each resulting egg cluster was placed in one of the following three photoperiods and the individuals reared to adult as described by McPherson (1971): 8L:16D, 8L:4D:8L:4D, and 16L:8D. The 8L:4D:8L:4D photoperiod exposed the animals to only 8 hr of continuous light but a total of 16 hr of light124 hr. All individuals were reared at 23.9 + 1.1" C during the light and dark phases, and in about 130 ft-c during the light phases (Ken-Rad, 15W Daylight, F15T81D). Adult characters compared were shoulder shape (ratio of lengthlwidth) and number of midventral abdominal spots (McPherson, 1974). These characters had previously been shown to be dimorphic between adults reared in 8L: 16D and 16L:8D (McPherson, 1979), Shoulder ratios were compared with Duncan's multiple range test (Table l), and number of spots with Fisher's exact probability test (Table 2). The 0.01 level of significance was chosen for all comparisons. l~inancial support was provided by the Office of Research Development and Administration, Southern Illinois University, Carbondale Graduate School. Project No. 2-10631. Z~epartment of Zoology, Southern Illinois University, Carbondale, IL 62901. 1McPherson: Effects of Continuous and Split Developmental Photophases DuringPublished by ValpoScholar, 197980 THE GREAT LAKES ENTOMOLOGIST Vol. 12, No. 2 Table 1. Comparison of shoulder shape (lengthlwidth) between E. t .  tristigrnus adults reared in continuous or split photophases during each 24 hr period. - - ShouldeP - Shouldera - Photoperiod Sex No. x Sex No. x aMeans followed by same letter within columns are not significantly different at the 0.01 level of probability by Duncan's multiple range test. Table 2. Comparison of number of midventral abdominal spots between E. t .  trisrigmus adults reared in continuous or split photophases during each 24 hr period. No. spots No. spots Photoperiod Sex 0-2 3-4 Pr0b.a Sex 0-2 3-4 P r ~ b . ~  aFisher exact probability test. RESULTS AND DISCUSSION There was no significant difference in shoulder ratios between males or females reared in the 8L:16D and 8L:4D:8L:4D photoperiods; all had shoulder ratios less than 1.00 (subtrian- gular shoulder = tristigrnus form) (Table 1). Those reared in 16L:8D had shoulder ratios greater than 1.00 (spinose shoulder = pyrrhocerus form). There was also no significant difference in number of spots between males or females reared in the 8L:16D and 8L:4D: 8L:4D photoperiods; most had 3-4 spots (= trisrigrnus form) (males, 90-95%; females. 95%) (Table 2). Those reared in 16L:8D generally had 0-2 spots (= pyrrhocerus form) (males, 75%; females 80%). These results show that the length of the developmental photophase, rather than the total amount of light, during 24 hr determines the adult morph. They also help to explain the function of the dark period. In previous experiments it had been assumed that the observed dimorphism resulted from the length of the photophase, not the scotophase. For example, in the experiments to determine the threshold photoperiod (McPherson, 1979), animals were reared in photo- periods ranging from 8L: 16D to 18L:6D. It was possible that the range of scotophases, not photophases, determined the results. In the above experiment. scotophases of 16 and 4 hr were involved in the production of the tristigmus form and 8 hr, the pyrrhocerus form. Thus, it appears that photophase does determine the morph, that scotophase is functioning only to break the photophase, and that the length of the scotophase is unimportant between 16 and 4 hr, perhaps less. LITERATURE CITED McPherson, J. E. 1971. Laboratory rearing of Euschistus tristigmus tristigmus. J .  Econ. Entomol. 64:1339-1340. . 1974. Photoperiod effects in a southern Illinois population of the Euschistus tristigmus complex (Hemiptera: Pentatomidae). AM. Entomol. Soc. Amer. 67:943-952. 2The Great Lakes Entomologist, Vol. 12, No. 2 [1979], Art. 4https://scholar.valpo.edu/tgle/vol12/iss2/41979 THE GREAT LAKES ENTOMOLOGIST 8 1 . 1975a. Life history of Euschistus tristigmus tristigmus (Hemiptera: Penta- tomidae) with information on adult seasonal dimorphism. Ann. Entomol. Soc. Amer. 68:333-334. . 1975b. Effects of developmental photoperiod on adult morphology in Euschistus tristigmus tristigmus (Say) (Hemiptera: Pentatomidae). Ann. Entomol. Soc. Amer. 68:1107-1110. . 1979. Effects of various photoperiods on morphology in Euschistus tristig- mus tristigmus (Hemiptera: Pentatomidae). Great Lakes Entomol. 1223-26. Van Duzee, E. P. 1904. Annotated list of the Pentatomidae recorded from America north of Mexico, with descriptions of some new species. Trans. Amer. Entomol. Soc. 30:l-80. 3McPherson: Effects of Continuous and Split Developmental Photophases DuringPublished by ValpoScholar, 1979

https://scholar.valpo.edu/cgi/viewcontent.cgi?article=1362&amp;context=tgle

Effects of Continuous and Split Developmental Photophases During Each 24 Hour Period on Adult Morphology in \u3ci\u3eEuschistus Tristigmus Tristigmus\u3c/i\u3e (Hemiptera: Pentatomidae)

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