i66 THE BIOLOGY OF INSECTS 



or ** suckers " are active little insects with firm cuticle, a 

 body of considerable depth dorso-ventrally, relatively long 

 feelers and legs, and well-developed wings (Fig. 43, a) ; they 

 fly and leap on the shoots of plants whose sap they suck for 

 food. These insects in their young stages are found between 

 the leaves of partially opened buds or clinging to the under 

 surface of the foliage, or in cavities due to the folding or 

 crumpling of leaves apparently resulting from a response 

 evoked by the irritation of the insect's presence, or in 

 definite galls arising in the same manner. In corre- 

 spondence with such environment, the young sucker has a 

 flattened body relatively broader than that of its parent, 

 rounded in front and behind. The early stages of the 

 Apple Sucker {Psylla malt) have been described by Carpenter 

 (1910) and by Awati (191 5). In the newly hatched young 

 the feelers and legs are short with fewer segments than in 

 the adult, and the head seems to be fused with the thorax, 

 as there is no division dorsally between crown and pronotum, 

 while ventrally the beak lies between and behind the bases 

 of the fore-legs. The cuticle is relatively soft and thin, 

 and the young insect diff"ers so markedly from its parent 

 that it may be called a larva — the general term (meaning 

 literally a *' mask ") applied to any young creature which 

 has to undergo transformation before it reaches the adult 

 state. The larval apple sucker (Fig. 43, c), after hatching 

 from its curiously stalked egg, wanders to a blossom-bud 

 outside which it waits until the scale-leaves open sufficiently 

 to allow it to crawl inside. Then amid the soft, crowded, 

 developing young leaves it finds shelter and abundance of 

 food, so that it grows quickly, passing through five stages 

 within the bud. In the second of these, as in the first, no 

 wing-rudiments are evident, but in the third and subsequent 

 stages wing-rudiments appear on the thorax ; the creature 

 has now become a nymph whose general body-form is still 

 markedly different from its parent, the prothorax not yet 

 marked off from the head, though the feelers and legs begin 

 to approach the adult proportions. Each of the first three 

 stages lasts about a week, the two later nymph stages 



