Essays Upon Heredity and Kindred Biological Problems. Weismann August

9.

      II. Neuroptera

      Phryganids ‘live in the imago stage for at least a week and probably longer, apparently without taking food’ (letter from Dr. Hagen).

      According to the latest researches Phrygane grandis10 never contains food in its alimentary canal, but only air, although it contains the latter in such quantities that the anterior end of the chylific ventricle is dilated by it.

      III. Strepsiptera

      The larva requires for its development a rather shorter time than that which is necessary for the grub of the bee into the body of which it has bored. The pupa stage lasts eight to ten days. The male, which flies about in a most impetuous manner, lives only two to three hours, while the female lives for some days. Possibly the pairing does not take place until the female is two to three days old. The viviparous female seems to produce young only once in a lifetime, and then dies: it is at present uncertain whether she also produces young parthenogenetically (cf. Siebold, ‘Ueber Paedogenesis der Strepsipteren,’ Zeitschr. f. Wissensch. Zool., Band. XX, 1870).

      IV. Hemiptera

      Aphis. Bonnet (‘Observations sur les Pucerons,’ Paris, 1745) had a parthenogenetic female of Aphis euonymi in his possession for thirty-one days, from its birth, during which time it brought forth ninety-five larvae. Gleichen kept a parthenogenetic female of Aphis mali fifteen to twenty-three days.

      Aphis foliorum ulmi. The mother of a colony which leaves the egg in May is 2‴ long at the end of July: it therefore lives for at least two and a half months (De Geer, ‘Abhandlungen zur Geschichte der Insekten,’ 1783, III. p. 53).

      Phylloxera vastatrix. The males are merely ephemeral sexual organisms, they have no proboscis and no alimentary canal, and die immediately after fertilizing the female.

      Pemphigus terebinthi. The male as well as the female sexual individuals are wingless and without a proboscis; they cannot take food and consequently live but a short time,—far shorter than the parthenogenetic females of the same species (Derbès, ‘Note sur les aphides du pistachier térébinthe,’ Ann. des sci. nat., Tom. XVII, 1872).

       Cicada. In spite of the numerous and laborious descriptions of the Cicadas which have appeared during the last two centuries, I can only find precise statements as to the duration of life in the mature insect in a single species. P. Kalm, writing upon the North American Cicada septemdecim, which sometimes appears in countless numbers, states that ‘six weeks after (such a swarm had been first seen) they had all disappeared.’ Hildreth puts the life of the female at from twenty to twenty-five days. This agrees with the fact that the Cicada lays many hundred eggs (Hildreth states a thousand); sixteen to twenty at a time being inserted into a hole which is bored in wood, so that the female takes some time to lay her eggs (Oken, ‘Naturgeschichte,’ 2^ter Bd. 3^te Abth. p. 1588 et seq.).

      Acanthia lectularia. No observations have been made upon the bed bug from which the normal length of its life can be ascertained, but many statements tend to show that it is exceedingly long-lived, and this is advantageous for a parasite of which the food (and consequently growth and reproduction) is extremely precarious. They can endure starvation for an astonishingly long period, and can survive the most intense cold. Leunis (‘Zoologie,’ p. 659) mentions the case of a female which was shut up in a box and forgotten: after six months’ starvation it was found not only alive but surrounded by a circle of lively young ones. Göze found bugs in the hangings of an old bed which had not been used for six years: ‘they appeared white like paper.’ I have myself observed a similar case, in which the starving animals were quite transparent. De Geer placed some bugs in an unheated room in the cold winter of 1772, when the thermometer fell to -33°C: they passed the whole winter in a state of torpidity, but revived in the following May. (De Geer, Bd. III. p. 165, and Oken, ‘Naturgeschichte,’ 2^ter Bd. 3^te Abth. p. 1613.)

      V. Diptera

      Pulex irritans. Oken says of the flea (‘Naturgeschichte,’ Bd. II. Abth. 2, p. 759) that ‘death follows the deposition of the eggs in the course of two or three days, even if the opportunity of sucking blood is given them.’ The length of time which intervenes between the emergence from the cocoon and fertilization or the deposition of eggs is not stated.

       Sarcophaga carnaria. The female fly dies ten to twelve hours after the birth of the viviparous larvae; the time intervening between the exit from the cocoon and the birth of the young is not given (Oken, quoting Réaumur, ‘Mém. p. s. à l’hist. Insectes,’ Paris, 1740-48, IV).

      Musca domestica. In the summer the common house-fly begins to lay eggs eight days after leaving the cocoon: she then lays several times. (See Gleichen, ‘Geschichte der gemeinen Stubenfliege,’ Nuremberg, 1764.)

      Eristalis tenax. The larva of this large fly lives in liquid manure, and has been described and figured by Réaumur as the rat-tailed larva. I kept a female which had just emerged from the cocoon, from August 30th till October 4th, in a large gauze-covered glass vessel. The insect soon learnt to move freely about in its prison, without attempting to escape; it flew round in circles, with a characteristic buzzing sound, and obtained abundant nourishment from a solution of sugar, provided for it. From September 12th it ceased to fly about, except when frightened, when it would fly a little way off. I thought that it was about to die, but matters took an unexpected turn, and on the 26th of September it laid a large packet of eggs, and again on the 29th of the same month another packet of similar size. The flight of the animal had been probably impeded by the weight of the mass of ripe eggs in its body. The deposition of eggs was probably considerably retarded in this case, because fertilization had not taken place. The fly died on the 4th of October, having thus lived for thirty-five days. Unfortunately, I have been unable to make any experiments as to the duration of life in the female when males are also present.

      VI. Lepidoptera

      I am especially indebted to Mr. W. H. Edwards11, of Coalburgh, W. Virginia, and to Dr. Speyer, of Rhoden, for valuable letters relating to this order.

      The latter writes, speaking of the duration of life in imagos generally:—‘It is, to my mind, improbable that any butterfly can live as an imago for a twelvemonth. Specimens which have lived through the winter are only rarely seen in August, even when the summer is late. A worn specimen of Vanessa cardui has, for instance, been found at this time’ (‘Entomolog. Nachrichten,’ 1881, p. 146).

      In answer to my question as to whether the fact that certain Lepidoptera take no solid or liquid food, and are, in fact, without a functional mouth, may be considered as evidence for an adaptation of the length of life to the rapid deposition of eggs, Dr. Speyer replies:—‘The wingless females of the Psychidae do not seem to possess a mouth, at any rate I cannot find one in Psyche unicolor (graminella). They do not leave the case during life, and certainly do not drink water. The same is true of the wingless female of Heterogynis, and of Orgyia ericae, and probably of all the females of the genus Orgyia; and as far as I can judge from cabinet specimens, it is probably true of the males of Heterogynis and Psyche. I have never seen the day-flying Saturnidae, Bombycidae, and other Lepidoptera with a rudimentary proboscis, settle in damp places, or suck any moist substance, and I doubt if they would ever do this. The sucking apparatus is probably deficient.’

      In answer to my question as to whether the males of any species of butterfly or moth are known to pass a life of different length from that of the female, Dr. Speyer stated that he knew of no observations on this point.

      The following are the only instances of well-established direct observations upon single individuals, in my possession12:—

      Pieris napi, var. bryoniae [male] and [female], captured on the wing: lived in confinement ten days, and were then killed.

      Vanessa prorsa lived at most ten

10

Imhof, ‘Beiträge zur Anatomie der Perla maxima,’ Inaug. Diss., Aarau, 1881.

11

Mr. Edwards has meanwhile published these communications in full; cf. ‘On the length of life of Butterflies,’ Canadian Entomologist, 1881, p. 205.

12

When no authority is given, the observations are my own.