The Garden Magazine, April, 1920 



101 



APPLE APHIS ON THE ELM 

 The "spring migrants" move into summer quarters on the 



leave the summer food plant and take flight — back to some 

 American Elm. 



Alighting on the bark, they seek a convenient crevice and 

 give birth to minute young, part of which are egg-laying females 

 and part males — this being the only time in the life cycle of this 

 insect that either of these forms is produced. These tiny "true 

 sexes" have no functional mouth parts and do not eat, their 

 chapter in the life history being concerned merely with mating 

 and providing for the deposition of the over-wintering egg. 

 Each female lays but one of these, the single egg nearly filling 

 her small body. 



This egg is the closing page of the life cycle for the fall, and 

 the opening one in the spring; because it is from this over- 

 wintering egg that the stem-mother hatches at the time of the 

 bursting leaf buds, in season to form the rosette of Elm leaves 

 for the spring habitation of herself and 

 her numerous progeny. And startling 

 as this life-round may seem, it is no 

 isolated example, for the histories of 

 many species of this family of insects 

 are most dramatic! 



TAKE that Elm leaf with a rolled- 

 under edge, for instance, hanging 

 on the branch not far from the rosette 

 just discussed. That leaf holds a story 

 as interesting as the one just told and 

 much like it, except that its spring 

 migrant seeks, instead of the Apple or 

 Hawthorn, the J uneberry or Shad-bush, 

 on the underground stems of which its 

 summer colonies dwell. And the simi- 

 lar rolled-under leaf of the English 

 Elm shelters an aphid that migrates 

 to the Currant to pass the heated 

 term. 



Nor are the Elms alone in serving 

 as winter and early spring residence 

 for aphids who spend their summers 

 in other parts. Among the common 

 spring leaf-feeding aphids which winter 

 in the egg stage on the Apple, for in- 

 stance, the migrant of one takes flight 



to Oats and certain other grasses, 

 where it has to be reckoned with as 

 one of the most serious of our grain 

 pests. Another species uses the Clover 

 as a summer resort — and for a change 

 in diet — after having wrecked the leaves 

 of the orchard it has inhabited early in the 

 season. The insect famous in economic 

 literature as the Hop aphid or Hop- 

 plant louse winters on the garden Plum, 

 as does a second species which migrates 

 to Thistles, and a third which eschews 

 the country for the greater refreshment 

 of a watering place during the hot 

 months — in other words a residence 

 aboard an Arrow-head or certain other 

 succulent plants (See The Garden 

 Magazine, December, 191 7) where it 

 enjoys a more or less complete change 

 of scene and diet. 



SO THE man who innocently plants 

 Lettuce near his or his neighbor's 

 Currant bushes is simply making mat- 

 ters convenient for one of the aphids 

 migrating from Ribes to members of 

 Apple the Compositae — and correspondingly 



difficult for the person who washes the 

 salad, for the leaf-green bodies of the apterous summer forms 

 of this species blend so well with the color of the Lettuce that 

 detection is almost impossible — and the insects cling more- 

 over, amazingly. 



All this considered, it is small wonder that the gardener ex- 

 claims, "where do these insects come from?" upon seeing aphid 

 colonies thriving where a few days before there were none; and 

 the question has as many answers as there are migratory species. 

 Which may seem distracting, though the knowledge is an ad- 

 vantage, for reference to the accompanyingtable will suggest that 

 not infrequently the dual personality of these remarkable insects 

 gives a double chance at their control; while with certain of 

 them, on the other hand, their opportunities of escape are 

 twofold because of added difficulties presented by their com- 

 plex existence. 



WHEN SUMMER COMES 

 A colony of woolly aphis that left the Elm and is established in its summer home on the Apple 



