304 THE PRACTICAL APPLICATION OF ECOLOGY 



attribute of nymphs in the gregarious phase. Faure gave the 

 tentative name of " locustine " for the products of the excessive 

 metaboHsm which lead to the development of the gregaria 

 coloration. He points out that the black coloration appears in 

 nymphs of the gregaria phase an hour or less after hatching. It 

 could not, therefore, he says, be possibly due to the activity of 

 the nymphs themselves and concludes that it is due to the passing 

 on of locustine from the female to the embryo in the nutritive 

 yolk of the eg^. The interesting problem of the biochemical 

 nature of the pigments concerned is as yet unexplored. The 

 morphological characters of the thorax which differentiates the 

 two extreme phases are also an expression of this activity. Strains 

 and stresses accompanying muscular exertion appear to exercise 

 an influence which moulds the thorax into the form characteristic 

 of gregaria — the more typical or ancestral form being retained 

 by individuals in the solitaria phase. The hypothesis that the 

 characteristic pigmentation of the gregaria hoppers is produced 

 as a by-product of high metabolic activity receives support from 

 recent experiments by Husain and Mathur (1936). These authors 

 found that when hoppers of the locust Schistocerca gregaria, in 

 the solitaria phase, were forced to crawl a certain distance daily 

 in revolving gauze drums and cylindrical cages that rotated 

 vertically at intervals, they assumed the black coloration 

 characteristic of hoppers in the gregaria phase. The pigmentation 

 of the latter phase was also induced when individual solitaria 

 hoppers were placed in cages crowded with hoppers of Poecilocerus 

 pictus and adults of Chrotogonus. 



In the phase solitaria the nymphs are relatively sluggish : 

 they sit about the food-plants quietly eating and undergo little 

 movement unless disturbed. We are still in the dark, however, 

 as to why mere crowding exercises an influence which appears to 

 activate a gregarious instinct — whether the actual stimulus 

 involved is, for example, contact, visual or odour, etc. Within 

 the limited space available it is not possible to discuss at all 

 adequately the immense and rapidly growing literature dealing 

 with the different aspects of locust life. The reader is referred 

 to the useful abstracts which appear monthly in the Review of 



