GARDEN PESTS IN NEW ZEALAND 



appears with all its characteristics. Some species take two years to 

 reach maturity. In this type of insect there is, therefore, no pupal or 

 resting stage, and the larval habits and food are the same as those of 

 the adult insect, while there is but little difference in structure through- 

 out all the stages. 



There are many winged insects (e.g., cockroaches, crickets and 

 earwigs) that show a slight advance toward a metamorphosis. Though 

 their larvae differ from the adults principally in the absence of wings, 

 there are stages between the younger larvae and the adults in which the 

 wing rudiments appear. These rudiments first appear after one of the 

 moults as small bud-like structures on each side of the thorax (earwig, 

 Fig. -t), becoming larger after each succeeding moult, when the 

 developing wings may be seen enclosed in a sheath of the cuticle; ait 

 the final moult the wings, no longer enclosed in their coverings, 

 straighten out and become functional. A very pronounced difference is 

 here noted between the wing development of such insects and that of a 

 moth, in that the wing rudiments of the former develop externally and 

 those of the latter internally. 



A decided advance toward a metamorphosis is exhibited by insects 

 known, as thrips (Fig. 4). Though readily overlooked on account of 

 their minute size (one-twenty-fourth of an inch and less), they are 

 nevertheless conspicuous on green foliage and white flowers owing to 

 their blackish or yellowish colour. Thrips, when magnified, are easily 

 recognised by their peculiar wings; each is feather-like, being formed 

 of a narrow rib-like membrane clothed along the margins with long 

 and delicate stiff hairs. Thrips' eggs are laidjipon the plant surface 

 or within the tissues, according to the species, and are very minute 

 (about one-twenty-third of an inch long). The larvae puncture the 

 plant tissues and feed upon the juices just as do the parents, which they 

 resemble in general form, except that there are no wings and the 

 antenna? are very short and the eyes small. There are two or three larval 

 moults, after which the insect is more like the adult, though still 

 resembling the larva. It now differs from the latter, however, in the 

 antennae being considerably shortened, and in the appearance of a pair 

 of finger-like processes on each side of the body attached to the thorax 

 and lying along the sides of the abdomen ; these processes are the sheaths 

 enclosing the wing rudiments of the future adult. The insect again 

 moults, changing to a form resembling the preceding stage in many 

 respects, but differing in the wing sheaths being much longer, and in 

 having the antennae, enclosed in sheaths of cuticle, turned back over 

 the head. Although during these two stages the insect is capable of 

 moving about, it is nevertheless sluggish and does not feed; from this 

 second semi-quiescent stage the adult emerges. In the thrip's cycle, 

 therefore, although the habits of the larva and adult are similar, the 

 presence of the two intermediate semi-quiescent stages, during which 

 feeding ceases, shows a decided advance toward a true metamorphosis 

 and represents a pupal stage. 



In the case of those insects not involved by a metamorphosis, as 

 discussed above, the structure and habit of both adult and the immature 

 stages differ but little, the development of wings being the principal 

 change, except in the case of the thrips, where there is a definite 

 tendency toward a pupa. However, passing on to a consideration of 



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