GARDEN PESTS IN NEW ZEALAND 



All insects do not follow the same method of development from 

 egg to adult, and the adaptations of structure and habit are many and 

 varied as well as simple and complex. Species having a complex 

 development, during which they pass through stages, each differing in 

 form from its predecessor,, undergo what is known as a metamorphosis; 

 contrasted with such insects are those developing in a simple manner 

 without pronounced differences in the form of successive stages, the 

 ycung resembling the adult in most features except size and maturity 

 these insects are without a metamorphosis. Intermediate between these 

 two extremes are other insects with a partial metamorphosis. 



A consideration of the life cycle of some common insects will serve 

 to illustrate the principles of development discussed above. Firstly, 

 will be taken examples of complex development or complete metamor- 

 phosis; secondly, examples of simple development or absence of 

 metamorphosis, followed by a review' of species having a partial 

 metamorphosis, thus linking the first two types. 



A convenient type of insect undergoing a complete metamorphosis 

 is any common moth (Fig. 4) ; one of the most suitable, most easily 

 obtained in all stages and commonest in any part of the country from 

 spring to autumn, is the magpie moth (Nyctemera amnulata) and its 

 caterpillar, the "woolly bear/"' The moth, unlike most oikits kind, is a 

 day-flying species, and is very conspicuous owing to its black colour 

 relieved by white wing spots, and orange-yellow bands on the abdomen ; 

 the equally conspicuous caterpillar, feeding on groundsel, ragwort and 

 cineraria, is black, with a very hairy body marked with narrow brick- 

 led lines. 



The eggs are laid in clusters by the female moth on the under side 

 of the leaves of the caterpillars' food-plant; at first the eggs are of a 

 pale green colour, but assume a darker yellowish tint within a few 

 hours, and finally a leaden colour some time later. These colour 

 changes are due to the developing embryo, and just before the young 

 insect (the caterpillar in this case) hatches, its outline as it lies curled 

 within the egg is easily seen through the transparent egg-shell; near 

 the top of the egg is a black spot marking the position of the cater- 

 pillar's head, while the numerous delicate black lines below the egg 

 surface are the black hairs with which the caterpillar is clothed. Accord- 

 ing to temperature and humidity, the incubation period that is, the 

 period between egg-laying and the hatching of the young caterpillar 

 varies from eight days to three weeks. The process of hatching occupies 

 about two 1 hours, the young insect using its jaws to eat an exit hole 

 through the egg. The caterpillar stage indeed, the first stage of all 

 insects is known as the larva. 



At first the larva of the magpie moth, measuring about one- 

 sixteenth of an inch long, is pale yellow in colour, except for the black 

 head and hairs clothing the body ; very soon, however, the body becomes 

 characteristically black, and develops the reddish lines. During growth 

 the larva feeds continuously day and night, undergoing from five to ten 

 moults before becoming fully grown. During a moult the cuticle of the 

 head is cast separately from that of the body. 



The body of the larva is worm-like, not only in general form, but 

 also in its segmented appearance ; it is, however, a very different animal 



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