A REVISION' OF THE GENUS LOCUSTA, L. 149 



According to the routine of the control work adoj^ted in Russia, all the swarms 

 were closely watched during their wanderings by the trained staff, and all the spots 

 where oviposition took place were marked out and also noted on the maps. Owing 

 to this procedure there was no doubt that in the following spring we had to conduct 

 the destruction work against the immediate progeny of those swarms. As soon as 

 the larvae in 1913 reached their third stage, when differences between migratoria 

 and danica are more apparent than in the earlier stages, it became evident that 

 although the bulk of the larval swarms consisted of migratoria, there were many 

 individuals which were certainly danica, these being different in coloration and showing 

 a tendency to desert the swarms. In spite of the intensive control measures, several 

 small swarms escaped destruction and attained their final moult ; these adult 

 specimens proved to be rather different from those of their parental swarms (see 

 line 6 of the table, p. 139). A rather large admixture of typical danica was very 

 obvious, but still more numerous were specimens of an intermediate character which 

 could not be identified either with rfawzca or with migratoria ; the bulk of the insects, 

 however, might have been referred to migratoria, but showed an obvious inclination 

 towards danica. in fact they had the pronotum more compressed laterally, the median 

 keel more raised, the elytra longer and the femora relatively shorter^ than in the 

 specimens from the parental swarms ; their coloration was also more variable. 

 The proportions are especially instructive when compared with those for the swarms 

 of 1912 ; in studying these figures one may see that the extent of variation was far 

 larger than in 19i2, and the average figures also changed in the direction of danica. 

 The swarms were not so dense as in 1912, and the individual insects showed obviously 

 less developed gregarious habits ; numerous single individuals of danica were scattered 

 all over the steppe, without any connection with the swarms ; the latter did not 

 undertake any migrations and gradually dispersed. 



Similar, though less striking examples are given in lines 7 and 8, 9 and 10 of 

 the table, in compiling which precautions were also taken to obtain the series most 

 likely to represent two successive generations. Unfortunately, I could not secure 

 rehable examples of more than two such generations from one spot. 



Breeding Experiments by V. PSotnikov. 



Though field observations like those described above are of great value, they 

 have the disadvantage of not affording absolute proof, and the only way to obtain 

 this is by breeding experiments. Such experiments have been undertaken by my 

 friend V. Plotnikov, in Tashkent, and, though conducted on a very moderate scale, 

 have yielded some most interesting and valuable results. Since all the actual 

 specimens from these experiments were given to me by V. Plotnikov, and are before 

 me now, I am able to give a httle more detailed account of the results than were 

 recorded in his original communication. 



In the summer of 1913 several specimens of both sexes of very typical danica 

 were isolated in cages, in which copulation and oviposition took place ; the eggs 

 hatched without hibernation, as is not uncommon with danica, but so far as we know^ 

 never occurs in migratoria. The description of the larvae and adults bred from them 

 is given by V. Plotnikov, as follows : — 



" The larvae had in the first stage a dark grey coloration, and not black as in 

 migratoria. In later stages they acquired various colorations — rmiformly green, 

 dark grey or brownish — but a number of them had the typical colouring of migratoria, 

 namely, a general reddish brown colour (sometimes greenish), with velvety black 

 stripes (broad or narrow) along the sides of the pronotal keel and black stripes on 

 the sides of the abdomen. The adults presented no characters typical of danica ; 

 the profile of the pronotal keel was usually straight, sometimes even concave. The 

 males were, however, smaller than the females." 



