A. J. Mangelsdorf.
Color and Sex in the Indian Walking Stick, Dixippus morosus.
Psyche 33:151-155, 1926.

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19261 Color and Sex in the Indian Walking Stick 151 COLOR AND SEX IN THE INDIAN WALKING STICK, DIXIPPUS MOROSUS
Harvard University, Bussey Institution,
In cultures of the Indian walking-stick, Dixippus rnorosus, reared in the insectary at the Bussey Institution, it was observed that in each generation there was a wide range of coloration varying from a uniform green in some individuals to a brownish black in others. Since this insect usually reproduces partheno- genetically the question as to the behavior in inheritance of the several color types appeared to be one of considerable interest. Dobkiewicz (1912) had already shown that the color of these insects is influenced by their surroundings. He reared
them in cages lined with colored paper, and found that those in green and yellow cages remained light green throughout their lives, while those in red and black cages had become quite black by the time they had reached sexual maturity. However, the occurrence in our cultures under what appeared to be a uniform environment of green and dark brown individuals, in addition to a number which were intermediate between the two extremes, suggested that there might be inherent individual differences in reactivity to a background of a given color. . To obtain further information on this question two females, one a light green and the other a dark brown, were isolated and their eggs saved. The eggs are dropped at the rate of two or three a day, and egg-laying may extend over a period of three to five months. Over one hundred eggs were obtained from each female. They were placed in wide-mouthed bottles stoppered with a cptton plug, and were stored in a damp situation in the insectary. In about five months after the first eggs were laid, hatching began.
Four cages were constructed,-two were lined with light yellowish-green cheesecloth and two with the same material of a very dark red color. After a number of eggs from both the green



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152 Psyche [December
and the brown parent had hatched, twenty-four young from each female were selected and divided into two lot,s of twelve each. One lot was then placed in a green cage, the other in a red cage.
The insects at this stage were uniformly of a dull green color. They were fed each night with shoots of Tradescantia fluminensis, the remains of which were removed each morning to avoid obs- curing the background.
No change could be observed after 'either the first or the second moult. After the third moult, however, those in the green cages had taken on a clearer, lighter shade of green, while those in the red cages had become perceptibly darker. After the fourth moult the difference was striking,-those in the green cages remained a clear green, while those in the red cages were dark brown. There was but little difference in the rate of-change between the progenies of the two females. Those from the green parent showed, if anything, a more rapid change to brown than did those from the brown parent.
To determine whether the change to dark brown could be effected in the later stages of the life history, two individuals were transferred from each of the green cages and placed with their sisters in a red cage After passing through several moults, they became almost dark as those which had occupied the red ca,ges from the beginning of the experiment , At the same time two brown individuals were removed from each of the red cages and were placed with their sisters in the green cages t,o determine whether the color change to brown is reversible. In each case the middle pairs of legs of the transferred individuals were removed to distinguish them from the others. After several moults they had taken on a somewhat lighter shade, and when mature they were of an indefinite greyish color; but the dark pigment was never completely resorbed. The middle legs, however, which were regenerated under the in- fluence of the green background were of a peculiar bluish-green shade, their color presenting a striking contrast to that of the rest of the body.
In each of these cases no differences could be observed in the reactivity of the two progenies.




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19261 Color and Sex in the Indian Walking Stick 153 After the insects had attained sexual maturity, two other green individuals were transferred to red cages and two dark brown individuals to green cages. No color change was observed. Apparently the color present after the last moult is permanent. The question as to the reasons for the original variations in color of individuals occupying the same environment as found in our cultures remains unanswered. The only explanation which suggests itself is the following: The insects feed during the early part of the night attaching themselves before dawn to a branch or any other suit'able support, and remaining motionless in the same spot throughout the day. They show a marked tendency, in captivity at any rate, to return to the same support day after day. If the slight differences which exist in the il- lumination and background are sufficient to bring about the differences in color, this habit may be responsible for the ob- served variation.
Fryer (1913), working with a bisexual walking-stick, Cli- turnnus cuniculus, from Ceylon, in which both yellow and green forms are found, interpreted the color differences as being in- herited. The color, according to his hypothesis, is due to action of a single factor pair, yellow being dominant over green His data, however, do not furnish the necessary proof for his hypo- thesis. The males are uniformly of the same color, and he was thus able to assign to the male used in a given mating the par- ticular genetic constitution necessary to explain the proportions obtained in the progeny; but apparently the tests necessary to determine the correctness of his assumptions were not made. The fact, as shown by Pantel and de Sinety (1918), that coloration in several other species of walking-sticks in addition to Dixippus, is dependent upon the environment, suggests the desirability of reexamining the behavior in Clitumnus from this viewpoint.
Among a total of several thousand individuals reared in our cultures, two males and one gymandromorph appeared. The sporadic occurence of males and gyinandromorphs has also been reported by others. Nachtsheim (1922) has suggested that non-disjunction is responsible for their appearance. In the Or-
thoptera generally, the female is characterized by the presence of



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154 Psyche [December
two X-chromoson~es, the male by one.
The loss of one X-chro-
mosome by non-disjunction or in any other manner would presumably recult in maleness. If the loss occurred before the first somatic division, the entire individual would be male,-if it occurred later a gynandromorph would presumably result. In the gynandromorph mentioned, the left
side throughout the
entire length was typically typically female, the right side was male, suggesting that the loss of an X-chromosome had occurred at the first somatic division.
One of the males was placed in a cage with several females which had just attained sexual maturity. Only females appeared in t,heir progenies. Copulation was not observed, but the insects were seldom examined at night. Nachsheim niated one of the males which appeared in his cultures with females and observed repeated copulation but with no effect upon the sex of the pro- geny,-as in the progenies resulting from unmated individuals, all were females. Since, according to Pehani (1924) normal sper- matozoa were produced by one of t,he sporadic males studied by him, it appears that the eggs have lost their capacity for fer- tilization.
In fornis whose eggs have the ability to develop partheno- genetically and where parthenogenetic reproduction results exclusively "n females, a trend in the sex ratio is automatically set up, which must end in the ultimate elimination of males unless this effect is offsst by some factor or factors such as greater viability of males or of male-producing spermatozoa, which tend to distort the sex ratio in the opposite direction. In the Orthoptera, fornis having the capacity for parthenogenetic reproduction are known in which males are never found, others in which males are rare, and still others in which the sex ratio is near equalit'y. It must be concluded that forms in the last category have developed t,he capacity for parthenogenesis only recently or, as already suggested, that the trend toward an excess of females, which would otherwise be an inevitable conconimitant of thelyotokous parthenogenesis, is being offset by other factors tending toward an excess of males.




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19261 Color and Sex in the Indian Waldinq Stick 155 Literature.
Dobkiewicz, L. von. Einfluss der iiusseren Umgebung auf die Farbung der indischen Stabheuschrecken, Dixippus moro- sus Biol. Zentralbl., 32. 1912, pp. 661-663. Fryer, J. C. F.
Preliminary Note on some Experiments with a Polymorphic Phasmid. Journ. Genetics, 3, 1913-1914, pp. 107-111.
Nachtsheim, H. Parthenogenese, Gynandromorphismus und Geschlechtsbestimmung bei Phasmiden. Zeitschr. f. Abst. u. Vererbgsl., 30: 287-289. 1923.
Pantel, J. and de Sinety, R. (1918). Reaction chromatique et non chromatique de ' quelques phasmides (Orthopt.) Bulletin Biologique, 52 : 177-283.




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