February, '16] PATCH: APHID ECOLOGY 49 



cycle with its winter and spring habitation on the plum and its summer 

 residence upon various water plants. 



Aside from the idiosyncrasies of the aphids as regards their life 

 cycles, their careers are difficult to follow on account of their elusiveness. 

 A species needs to be very abundant, indeed, in order to give a field 

 demonstration of its migratory actions. During ordinary seasons 

 it is like looking for a needle in a haystack to obtain field data, even 

 when you know what vegetation to watch. 



And the difficulties are not by any means eliminated by bringing 

 the material into the laboratory. Aphids are exacting — they must 

 have succulent food plants with a good supply of sap or a "hunger 

 strike" ensues which means death to the colony and very likely an 

 indefinite postponement of the solution of the problem. Migratory 

 tests ought to be proved out on plants grown from the seed to be 

 absolutely sure of clean stock. Where this is impossible, the test 

 plant should be brought into the greenhouse at least several weeks 

 before migration begins, for two reasons: To secure uninfested material, 

 and to give it an opportunity to get well rooted and ready for growth. 

 It is not an easy matter to grow indoors some of the most common 

 weeds under control conditions satisfactory to the demands of the 

 experiment. I have had repeated failures (and but one success) try- 

 ing to establish cardui migrants from plum upon thistle apparently 

 only because I have not mastered the art of growing a healthy thistle 

 under an aphid cage. 



Even aside from the question of the health of the plant, there seems 

 often to be an individual immunity of certain plants against aphid 

 attacks. It is no uncommon thing to find one Norway spruce free 

 from galls of Chermes abietis although its branches may touch a second 

 Norway spruce heavily laden with these growths. One spring I 

 stocked about sixty apple seedlings with lanigera migrants from elm 

 rosettes and vigorous colonies were secured on but two of them. 



Again different species vary exceedingly as to the behavior of their 

 migrants. Some species, it is true, will plunge their beaks into the 

 proffered food plant within a few hours and begin to establish their 

 colony of young the first day and all is placid and straightforward. 

 Other migrants, when removed from their primary host, will rest for a 

 day or two or even longer quietly upon the leaves of anything that is 

 offered them, and then suddenly, when the hour for flight has arrived, 

 they take to their wings and fly as energetically away from their 

 proper food plant as toward it, for it is their instinct to fly, and fly they 

 must before they settle. Others are manageable when handled in 

 small numbers and will settle quietly under such circumstances when 

 they become excited if introduced into a cage in large numbers, and 



