GARDEN PESTS IN NEW ZEALAND 



CHAPTER V. 



Sucking Insects. 



THE term "sucking insect" is applied to all insects that have the 

 mouth parts modified as delicate stylets, by means of which the 

 plant tissues are punctured and the nutrient sap sucked up. Not only 

 may such insects weaken the infested plants, but they also cause the 

 destruction of chlorophyll, interfere with the normal functioning of the 

 stomata, and have a toxic effect upon .the tissues; further, many sorious 

 plant diseases are earned and spread by sucking insects, whilst the 

 punctures made when feeding may allow the entry of disease spores. 



Among sap-sucking insects are scale insects, mealy-bugs, aphids. 

 leaf-hoppers, white-flies, thrips, etc. Infestation by most of these 

 insects (especially in the case of scale insects, mealy-bugs, and aphids) 

 is very often detected by the sticky nature and blackened appearance 

 of the plants; this is due to the fact that the insects excrete a sweet, 

 sticky substance known as "honey-dew," which collects! on the foliage 

 and branches, whilst upon it grows a black, sooty mould. 



Scale Insects and Mealy-bugs. 



Scale insects and mealy-bugs, collectively known as coccids, are of 

 very great economic importance on account, not only of their widespread 

 depredations upon plants, few being free from infestation, but also of 

 the commercial value of some species e.#.; in the production of lac. 

 cochineal, Chinese wax, etc. ; it is with the injurious forms that the New 

 Zealand horticulturist is concerned. The term "scale insects" is derived 

 from the appearance of many of the species that are protected by a 

 scale-like covering, which forms a conspicuous scaly incrustation when 

 a plant is heavily infested. 



Of the several kinds of insects injurious to vegetation, the coccids 

 as a family are undoubtedly of major importance, because they infest 

 not one group, or allied group, of plants, as do so many other injurious 

 insects, but an extensive range of widely different plants. Some coccids 

 are much more injurious than others, the San Jose Scale, for example, 

 having a very virulent toxic influence, while the Greedy Scale may 

 cause but little damage, even when the plant is completely encrusted by 

 it; further, some plants may be more susceptible to injury than others 

 by the same species of coccid. 



Coccids, as a whole, are highly specialised insects, and among 

 themselves exhibit a great variety of forms. Throughout the group the 

 sexes differ to a marked degree. The adult males, which vary but little 



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