

PRESIDENT'S ADDRESS. Ixxxvii. 



the individuals of the same species would acquire wings at about 

 the same date, and then fly on the first suitable day, whilst the 

 others might all attain their imago state at the later date. 



I have always understood that these small ponds were believed 

 to be stocked with water-beetles (and I suppose any other 

 winged water insects such as water-boatmen) by immigrants 

 flying from other pieces of water, but I have not come across 

 any account of a migration such as the present one, though it 

 must surely be of not infrequent occurrence, and likely to be 

 observed by those who keep their eyes open for such things. It 

 is not even mentioned by Mr. Tutt, whose valuable papers on 

 "The Migration and Dispersal of Insects" (Entomologist's 

 Record, Vols. X., XL, XII., XIII.), have brought together an 

 immense number of observed instances in the case of many 

 species, and to whom any writer on the subject must be greatly 

 indebted. 



The only other insects in this order which appear to be known 

 as migrants are the cuckoo-spits, of which one case of migration 

 is recorded, and the Aphides or plant-lice, more familiar to many 

 under the name of green-fly. Of these migrations there are two 

 totally distinct sorts. In the first, which is, I believe, confined 

 to certain species, there is a regular annual movement from one 

 species of plant to another, caused by the dying away of the first 

 kind of plant and the necessity of seeking fresh food. Lichten- 

 stein has traced, amongst others, this migration in the hop Aphis 

 (Phorodon humuh\ which feeds on the hop plant whilst it is 

 green, but in the autumn, when the hop plant dies back, it 

 migrates to plum trees (Prunus sp.), on which it remains until 

 the hop is again fit for its reception. Parthenogenetic viviparous 

 reproduction takes place on both plants, but eggs, which survive 

 the winter, are laid only on the Prunus. Many of these species 

 which migrate in this manner have been known for long and 

 supposed to be distinct species, attached to two distinct 

 plants. 



