236 THE entomologist's record. 



Tetraneura idmi fed on the rootlets of maize [Zea mais), and his 

 observations showed that the " fundatrix" comes out of eggs deposited 

 in the crevices of the trunks of ehns in the beginning of May, and 

 forms a gall on a leaf. He also showed that in the gall the "funda- 

 trix " deposits a great number of young, which all acquire wings. 

 These migrate and deposit young, which are apterousand subterranean, 

 feeding on roots of maize for a fortnight. The descendants of these 

 apterous forms develop wings and return to the elm trunks. Here 

 they produce sexual forms, which copulate and lay eggs, and thus 

 complete the cycle. 



Lichtenstein later proved that Pemphigus indlida of the elm 

 migrated to mint, and produced the form previously known as 

 lihizohius menthae, which in turn went back to elm. Also that 

 l'em2)higus bm-sarius migrated from poplar to Sonchus, producing 

 Tlhizobiiis sonchus, which in turn went back to the poplar, etc. 



The migration of Phylloxera vastatrix is somewhat difi'erent. 

 This species winters on the roots of the grape-vine, in an apterous 

 condition, and the apterous form commencing to grow rapidly in 

 spring, produces viviparous young, which are also wingless and 

 sexless, and continue to produce young asexually. About midsummer 

 some individuals acquire wings, and migrate to other vineyards in their 

 vicinity. These migrants lay eggs of two sizes, the larger of which 

 produce sexual females, the smaller, males. These sexual insects 

 exhibit many modifications when compared with the asexual form. 

 They cannot fly nor feed, for they have no wings, and the mouth 

 organs are aborted. After pairing, a single egg is produced by the 

 female, and this produces an asexual form, which will be ready to go 

 on with the work of reproduction (and destruction) the following spring. 



In these cases it will be observed that the migration of the gall- 

 making aphides and Phylloxera is directly connected with the food- 

 supply, the winged forms selecting a plant on which the asexual forms, 

 resulting from the " stem-parent " emerging from the fertilised egg, 

 will find nourishment for their parthenogenetic progeny. 



The general dispersal movements of aphides, i.e., those instances 

 in which large numbers of winged aphides change their location in- 

 vast swarms, are of an entirely different character. These swarms are 

 the parthenogenetic progeny of the "stem-mothers," which are 

 produced in spring from fertilised eggs. The "stem-mother" is 

 wingless, and grows rapidly by sucking the juices from the leaves of 

 the plants on which it finds itself. All the young born of this " stem- 

 mother " are also without sex, i.e., they are not sexually developed 

 females, and each is capable, in a few hours, of producing viviparous 

 young. The fecundity of aphides is almost incredible. It has been 

 estimated that many millions are produced from a few parents in the 

 course of a few weeks at most, under favourable conditions. Un- 

 favourable meteorological conditions, however, soon check their in- 

 creas-e, and the influence of the weather in early spring is often such 

 that it determines whether or not the insect will be a pest later in 

 the year. 



Assuming the weather conditions, however, to be favourable, 

 viviparous reproduction goes on at a very rapid rate. By means of 

 artificial heat Kyber kept up the viviparous reproduction of certain 

 aphides for four years, the progeny of which, at the end of that time, 



