INVESTIGATIONS ON THE MUTILLID WASPS 15 



The variation in size of individuals of the same species was noted 

 by Hoffer (1886) and he attributed this difference to the food supply 

 of the Mutillid larva. The following is a translation of his para- 

 graph on this subject. 



Regarding the size of single individuals of Mtitllla europaea, there is an 

 extraordinary difference in this respect ; it depends upon the size of the bum- 

 blebee pupa consumed by it ; therefore a female, which has developed from an 

 enormous female of Bombus mastrucatus, is extraordinarily larger than 

 another which has been forced to feed on the worker pupa of Bomhus agrorum, 

 so that one may mistake the two size differences very easily for species differ- 

 ences. The largest female of my collection (developed from a female pupa of 

 B. nmstrucatus) measures more than 26 mm. in length, the smallest (from a 

 nest of B. agrorum) is scarcely 10 mm. long. 



This kind of variation was also brought to the notice of the writer 

 very forcefully in the case of Dasymutilla Moculata Cresson, where it 

 was found that the individual specimens could be arranged in series 

 of two different sizes, apparently representing two different species. 

 A detailed study of this species was made in 1922 and 1923 and 

 reported on (1924) as follows: 



That there are variations in size among individuals of the same species of 

 insect is well known among entomologists and has been the subject of a number 

 of investigations. These have had as their object either collection of data re- 

 garding the character and extent of the variations, or the demonstration of 

 the causes for the phenomenon itself. The variations which are present in 

 various species of animals and plants may be divided into two very funda- 

 mentally different classes : those which are genetic in character, and those of 

 an ecological nature. Variations of the first class are due to some reaction that 

 occurs in the germ plasm, while those of the second class are due to the effect 

 of some stimulus in the environment, and are therefore ecological. The prin- 

 cipal ecological factors which have been suggested as causes for variation in 

 size are temperature, humidity, light, chemical stimuli, and nutrition, the last- 

 mentioned including both quantity and quality of food. An excellent review 

 of the literature on this subject has been made by Bachmetjew.' In the case 

 to be discussed the factors of temperature, humidity, light, chemical stimuli, 

 and quality of food apparently vary in a uniform manner, while the quantity 

 of food is small in some cases and large in others. 



The quantity of the food supply has been used by a number of authors to 

 account for the variations in size which occur within the same species of 

 insect. Koch^ studied the lepidopteron Vanessa io var. joides Dahl and con- 

 cluded that it was a variety based on small specimens of Vanessa io and that 

 their small size was due to the starvation of the larvae. Berlepsch ' performed 

 an experiment with the larvae of queen bees and states that he was able to 

 reduce the size of the queens by reducing the food supply of the larvae. 

 Kleine* states that worker bees of inferior size are produced from poorly fed 



1 Bachmetjew, P. 1907. Experimentelle Entomologische Studien, vol. 2, pp. 29&-312, 

 596-597, 765-768. Staatsdiuekerei, Sophia. 



2 Koch, G. 1856. Die Schmetterlinge des westlichen Deuschlands. Kassel. 

 'Berlepsch, A. v. 1860. Die Biene und die Bienenzucht in honigarmen Gegenden nach 



dem gegenwiirtigen Standpunkt der Theorie und Praxis. Muhlausen im Thiiringen. 



*Klelne, G. 1867. Uuber das Gesetz der Entwickelung der Geschlechter bei den 

 Insktn. Zeitschr. fiir wissnsch. Zool., vol. 17, pp. 533-558. 



