GARDEN PESTS IN NEW ZEALAND 



insects that destroy vegetation ; they are of much greater value in thife 

 respect than birds. In. recent times the utilising of beneficial insects as 

 a means of pest control has developed as one of the most important 

 branches of entomological research. 



From a general viewpoint, the beneficial insects are to be found 

 mainly among the groups, including wasps, beetles, flies (two-winged 

 insects) and lace-wings. The following are some examples : 



Common examples of parasitic insects are the ichneumon wasps 

 (Fig. 14a), chalcid wasps (Fig. 14b), and ensign wasps, the first being 

 the most conspicuous, the others less so owing to the minute size of 

 many of them. A characteristic feature of these forms is the stalk-like 

 attachment of the abdomen to the thorax and the sting-like ovipositor of 

 the female, which may be of short or moderate length, sometimes pro- 

 jecting as a tail-like appendage beyond the end of the abdomen. Para- 

 sites deposit their eggs either upon or within the body of their victims 

 or hosts, which are eventually destroyed by the larvae hatching from the 

 parasites 7 eggs. Destructive caterpillars and their pupa?, and also 

 aphides, are attacked by these wasp-like parasites, which in many cases 

 restrict their depredations to one or a limited number of host species, 

 while others are more general in their selection. Another group, the 

 predaceous wasps, should be mentioned here. These insects in the adult 

 state are hunters, and capture and paralyse by stinging such insects as 

 caterpillars and flies, as well as spiders, which are stored in nests or 

 cells for the nourishment of the predators' offspring. 



Important natural enemies of aphides and young caterpillars are the 

 hover-flies, which can be easily recognised by their manner of flight. 

 They are two-winged insects (Fig. 14c), and when on the wing hang 

 motionless, as if suspended by some unseen means, to suddenly dart off 

 with marvellous rapidity, until they hang motionless as' before. These 

 flies lay their eggs upon the foliage of plants infested by aphids or 

 caterpillars, and from these eggs legless and headless larva? emerge 

 (Fig. 14d), and commence to search for and feed upon their victims. 



Another important group of two-winged flies is the tachinids. They 

 are rather robust, usually very bristly (Fig. 14e) ; they vary in size from 

 that of a large blue-bottle to comparatively minute forms. The 

 tachinids lay their eggs either upon their hosts or on the food plants of 

 the latter, where they can be swallowed; some tachinids give birth to 

 living larvae, which crawl about in search of their victims. 



Among the beneficial beetles are the well-known ladybirds ( Fig. 

 14f ) ; they are mostly oval in outline, dome-shaped above and flat below, 

 while many of them are spotted by yellow, red, or white in a char- 

 acteristic manner, though others are of one uniform colour. The eggs 

 are laid on plants infested by the aphides and scale insects upon which 

 the beetles and their larvae (Fig. 14g) feed. There are other kinds of 

 beetles of importance as predators, such as the common tiger-beetle, but 

 they are not especially selective in their types of victims. 



A very valuable group of insects includes the lace-wings or aphis- 

 lions. The adult insects (Fig. 14h) carry the seemingly over-large 

 lace-veined wings roof -like over the small body; the larvae are alligator- 

 like (Fig .14i), and possess a pair of caliper-shaped jaws, by means of 

 which they capture their prey. The eggs are laid directly on plants or 

 are attached at the end of long stalks. 



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