Werner Marchand.
First Account of a Thermotropism in Anopheles punctipennis, with Bionomic Observations.
Psyche 25:130-135, 1918.

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130 Psyche [December
strongly punctate. Head emarginate in front and consequently very thin anteroposteriorly. Antennae brown-black, hairy. Legs brown, trochanters, tips of tibiae and tarsi pale or whitish. Wings hyaline, fringed with long hairs, forewings with a brown band ex- tending across the stigma1 region and another at the apical margin." FIRST ACCOUNT OFATHERMOTROPISM IN ANOPHELES PUNCTIPENNIS, WITH BIONOMIC OBSERVATIONS. BY WERNER MARCHAND.
Department of Animal Pathology, Rockefeller Institute for Medical Research, Princeton, N. J.
In the fall of 1915, while taking part in a survey of the breeding- places of Anopheline mosquitoes in the neighborhood of Princeton, in cooperation with the local Mosquito Extermination Commission, the writer made certain observations on the mosquitoes encount- ered. This account is restricted to a few facts which appear to be new or serve to clear up some doubtful point in the life history of the mosquitoes.l
I. Bionomics of the Larvce.
In the Princeton region, only two species of Anopheles have been recorded, these being A. quadrimaculatus and A. punctipennis. The latter species is by far the more common, but, since King's experiments (1916); it cannot be regarded as entirely harmless. It is doubtful, however, whether this species, which has been found to occur as far north as Boston, Mass. (Th. Smith)? is also in the northern states a regular carrier of malaria. The larvae of A. punctipennis were kept captive in large numbers and lived best in a flat dish which was left uncovered in order to give free access to the air. In a dish about eight inches in diam- 1 The "writer wishes, on this occasion, to express his thanks for the kind helpfulness through which his work was facilitated by Professor E. G. Conklin and Professor Ulric Dahlgren of Princeton University.
Dr. Conklin also had the kindness to revise the English of the MS. 2 King, W. V. Experiments on the development of malaria parasites in three American species of Anopheles.
Jour. Exp. Med., Vol. 23, pp. 703-716,1916. 8Theobald Smith.
Notes on the Occurrence of Anopheles punctipennie and Anopheles quadrimaculatus in the Boston suburbs. Jour. Bost. Society of Medical Sciences, Vol. V, pp. 321-324.1901.




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19181 Marchand-A Thermotropism in Anopheles punctipennis 131 eter, filled to a depth of about one and one-half inches with water from a pond, more than two hundred Anopheles larvae, mostly collected in a half-grown stage, many of them in very young stages, developed into pupae. The pupae when formed were taken out with a pipette and transferred to another jar with provisions for the adults to hatch.
In order to rear Anopheles larvae successfully, it is necessary to feed them, and this fact has not been sufficiently emphasized. It was found that certain unicellular surface algae, the species of which could not be determined, form a very satisfactory food. These algae developed freely in one of the glass-covered aquaria in the Vivarium of Princeton University. In this aquarium they covered the whole surface of the water in a continuous green sheet, which was wrinkled and folded in places through the excessive develop- ment of the algse. In order to transfer these to the culture dishes it was sufficient to dip the finger into this stratum and then dip it into the Anopheles-basin; here the algse, upon reaching the clear surface of the water, would immediately spread out over the whole surface in the form of a thin, opaque, green layer. The Anopheles larvae would at once start feeding upon these minute algae, a clear area soon forming around the head and mouthparts of each larva. Before evening, the larvse had cleared the whole surface of algae. The procedure was repeated at night in order to provide food for the larvae to last until the next morning, when again the algse had been completely devoured. In this way they were fed regularly twice daily. Under ordinary conditions, when Spirogyra or other filamentous algae are given as food (C. A. Smith),l many larvae usually die, because, as a matter of fact, their natural way of feed- ing is at the surface. Howard, Dyar, and Knab (1912)2 suggest that, to provide food the jars in which Anopheles larvae are grown, should be kept uncovered, "in order that the dust from the air may settle continuously upon the water." Undoubtedly, the Ano- pheles larvae may feed on surface bacteria or protozoa, but in absence of green plants, the contamination of the water often causes death. When surface algae are given, as in the case here recorded, practically no larvae are lost, because these algae produce oxygen 1 Cora A. Smith. The Development of Anopheles punctipennis Say. Psyche, Vol. XXI, p. 1. 2 Howard, Dyar, and Knab.
The Mosquitoes of North and Central America and the West Indies. Vol. I, 1912.




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182 pmche [December
in abundance, and the water does not nave to be renewed at all. The quantity of algte devoured by the lam was quite considerable, Lack of attention to this detail may perhaps explain the frequent failures in rearing Anopheles larvse.1 On the other hand, the use of surface alp as food may serve to determine with exadness the quantity of food coniumed by a single larva, since the algse, under carefully chosen conditions, covet the surface quite evenly in a layer of measurable thickness, and therefore the quantity of algse present on a surface of given dimensions and consumed in a given time may be estimated or calculated, and, divided by the number of larvae feeding on this surface, would give the quantity consumed by a. single larva. However, as the season was advanced, and the larvae were transforming into pupse, this experiment was not carried out.
The larvse showed in a remarkable degree the characteristic in- stinct spoken of by 7atek,2 to drop to the bottom when a shadow passed over their heads. When the writer came near them, in the morning, after they had been completely undisturbed for many hours, the phenomenon was particularly striking. The larvae would drop almost simultaneously and then would remain at the bottom for several minutes.
In this connection, it may be noted that Graham has stated that, in the Sudan, microscopic fresh-water algse form the principal food of Anopheles, a fact not unimportant for their control, since it may be that the mosquitoes may be kept in check by methods aiming at a destruction of the algse.#
II. BWnomics of the Adult Stage.
The resting position of Anopheles has often been used as a char- acteristic to distinguish the malarial mosquito from other species, the Anopheles holding the body, as a rule, at a certain angle to the surface on which they are resting. This angle is, in A. pitnetipmnia, usually about 45'; Nuttall and E hipley's illustration as reproduced 1 W. M. Graham (A study af Moaquita larva, Jaw.-Ent. Reaearcli, Vol. I, W10) toa BUM torreotly that failure to real the iiu-vie in not to bÌ wondered at when It if recognized that mm- quito k m require a coastant supply of awdal food. conaiating uaiialty of li'ring fresh-watef dm. In the abaende of algm the lam become cannibalistic and dmhy one another. * iiettk, James. Behavior of Amphifff a.I6(manå´t1 Wiedfimmn KtA taiaiin&culatun Go*. Ann. Est, 8oc. of AlaCTica, ViTI, 1915, p. 221 ff. 8 Graham, Ion. ait.: these aim were not mrfm aIga but were auspenctod in the water: a> stated, however, the Anopheles lama is mainly a surface feeder.



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19181 Marchand-A Thermotropism in Anopheles punctipennis 133 by J. B. Smith (Mosquito-control exhibit, N. J. State Museurn),l in which it is represented to form a right angle with the surface, is Fig. 1. Resting
position of hiber-
nating female of
Anopheles quadri-
maculatus.
Sketch-drawing
from Life.
an extreme case and not quite typical.
It seems,
however, that mosquitoes which rest for many hours in the same place, assume a more oblique position than do these which have just alighted. These characteristics apply only to Anopheles punctipennis, not to A. qu,adrimaculatus. Hiber- nating females of the latter species were ob- served beyond doubt in a resting position in which the body was held about parallel to the resting surface, as illustrated in the accompany- ing drawing from nature (Fig. 1).
Hence, they
can be easily mistaken for Culex if only the resting position is taken as a ~riterion.~
Concerning the biting position of Anopheles, Nuttall and Shipley's illustration (J. B. Smith, N. J. State Museum exhibit) is not entirely correct (Washburn),3 and H. P. Johnson4 is in error in assuming that the mosquito must necessarily bite with proboscis inserted at a right angle.
As a matter of fact, A. punctipennis
will insert the proboscis usually at an oblique angle, the mosquito biting in a position much like the resting position, and the line of the proboscis forming the continuation of the longitudinal axis of the body. This is evidently of advantage for the sucking mech- anism.
111. , The Biting Instinct due to a Thermotropic Reaction. Observations were also made on the biting instinct, which as it seems, is determined mainly by thermotropism. Patton and Cragg (1913) have reported5 that Howlett observed that females of 1 Nuttall and Shipley. The structure and biology of Anopheles miculipennis, Jour. of Hygiene, 1901.
Howard (loc. cit. p. 205) has recorded the same fact for A. quadrimaculztus hibernating in barns in southern Idaho.
8 Washburn, I?. L. Economic Entomology at the World's Fair. Science N. S., Vol. XX, No. 518, 1904, and "The Biting position of Ano.-.heles." Science, N. S., Vol. XXI, p.
228, 1905.
4 J. B. Smith. How doea Anopheles bite?
Science, N. S., Vol. XXI, pp. 71-72, 1905. 5 Patton and Cragg.
Textbook of Medical Entomology. London, Madras and Calcutta, 1913.




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[December
Stegomyia scute0a.k were attracted by the hot air radiating from a test tube filled with hot water. On the other hand, shed blood and sweat did not attract the Q 9 of this species sad Cidesfafigans any more than -water.
Hewlett's experiments were not known to
me at the time when these observations were made, and since they were obtained independently of other observers, and the phenom- enon was not known to apply to Anopheles, I may briefly report on them here, especially as data on thermotropism in insects are very scanty. The Anopheles which were kept in lamp chimneys for other purposes, were fed on apple jelly which was spread out on a glass plate. In order to prevent the mosquitoes soiling their legs and wings, the jelly was covered with filter paper. In the inten-
tion of providing a food as natural as possible, I heated the apple jelly on the glass assuming that it would then be taken more readily. This was in fact the case.
The mosquitoes came quickly
to the filter paper and would bite through it as if it were human. ,f'
Pig. 2. Antnigement used in demonstrating the thermotropism of mosquitoes. &in.
The question suggested itself whether they were attracted by the odor of the jelly or, possibly, by the heat radiating from it. Being curious whether the mosquitoes would be attracted also by heat alone, I substituted for the glass plate which was covered with jelly, a c1can one which was heated to a degree fillr1y above human body temperature but, of course, not excessive, and covered with



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filter paper in the same way as before, in order to provide a foot- hold for the insects. The mosquitoes were attracted under these conditions in the same way as if food had been present, each one attacking the surface of the filter paper which covered the glass plate, and all bending their proboscis in repeated efforts to pierce the surface. The number of mosquitoes used was about five or six at a time. The arrangement was that given in the diagram (Fig. 2). If several mosquitoes are used in biting experiments, there will usually be some individuals which will show no inclina- tion to bite, but the percentage of individuals not attracted by the heated glass plate, was about the same, and not greater than in the biting experiments. The males showed the same tropism as the females but much less strongly. As soon as the glass plate had cooled off, the mosquitoes became indifferent. However, the experiment could be repeated with the same mosquitoes as also with different sets and always with the same results. These observations, taken together with those made by Howlett, indicate that this thermotropic reaction is a very important factor to be considered in the analysis of the bloodsucking instinct. I have, since, tried to confirm these facts by observations on other species of mosquitoes, but so far have used only the hiber- nating females of AZdes sylvestris.
These, however, did not show
even a trace of the thermotropic reaction observed in A. puncti- pennis. On the other hand they also consistently refused to bite, though various food other than blood was readily accepted. Fe- males of Anopheles are known to bite occasionally in winter, and therefore, usually hibernate in stables where blood can be obtained (Grassi and others; see Howard, Dyar and Knab),l while Aedes which hibernates in cellars, seems not to bite at all during the winter even if brought into a heated room.
The absence of thermotropism
would, therefore, in this case, be only an adaptation to the con- ditions of hibernation, during which no blood food is taken, and it is perfectly possible, that Ai?des sglvmtris will be found thermo- tropic during the "biting season" unless, in this genus, other tropisms are involved.




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