GARDEN PESTS IX NEW ZEALAND 



In their life-histories and habits aphides present many variations, 

 sometimes of considerable complexity, but fundamentally the processes 

 are as follows: Eggs are laid on the host plant during the autumn, 

 and give rise to windless females in the spring; these females (being 

 asexual or parthenogenetic, since they reproduce without being ferti- 

 lised) a?e viviparous, producing living forms similar to themselves. 

 Some of these forms remain wingless, while others may develop wings, 

 upon which a wider dispersal of the species depends, but in both cases 

 such females are asexual and viviparous. Several such generations ma} r 

 develop until the autumn, when males and females appear, the latter 

 being oviparous, producing the over-wintering eggs when fertilised by 

 the males. Very often, however, the life-cycle is considerably compli- 

 cated by the winged forms flying to other host plants and establishing 

 there colonies differing in many respects from the parent stock; from 

 these secondary hosts there is a return migration to the original species 

 of plant. Again, the migrations may be restricted to different parts of 

 the same plant, from the leaves or branches to the roots, for example. 

 Most aphides are readily controlled by means of insecticides, such as 

 nicotine-sulphate, or kerosene-emulsion. They are also very often held 

 in check by natural enemies, such as aphis lions, hover-flies, ladybirds, 

 and numerous forms of hymenoptera. The following species are some 

 of the commoner aphides met with in Xew Zealand : 



BLACK PEACH APHIS (Aphis persico'-riiger). From early spring, 

 even before the foliage develops, this aphis may be found heavily 

 infesting the young, succulent shoots of peach; it also occurs on cherry, 

 plum and nectarine. The adult insects are black and the immature 

 stages pale reddish-brown, dull brown, or lemon-yellow. During the 

 winter the insect lies underground about the roots of the host plant, and 

 thence migrates to the young growth in spring. At first only wingless 

 forms are seen, but as the season advances the winged migratory aphides 

 develop; at that time the foliage is so severely attacked that it becomes 

 crumpled and functionless (Fig. 9, 1), while the developing fruit is 

 distorted and rendered useless. The heat of the late summer destroys 

 the aphides still on the foliage, but sufficient numbers descend under- 

 ground for protection, where they live over winter. 



GKEKX PFACH APHIS (Rhophalosiphum persicce). - - This aphid 

 occurs on a wide range of plants, including the pea.ch, and, as a rule, is 

 most abundant during summer and autumn; as the name implies, the 

 general colour is green, though some individuals are reddish or brownish- 

 yello'W; the wingless forms have black-tipped "cornicles," and on the 

 abdomen of the winged insects are dark markings. 



BLACK CHERRY APHIS cm FLY (Myzus cerasi). This aphid has now 

 a world-wide distribution. In Xew Zealand it has been found on 

 cherry and plum, though in other countries its hosts include peaches, 

 red and black' currants, and cruciferous plants, such as common mustard, 

 shepherd's purse, etc. This species exudes copious honey-dew, upon 

 which sooty mould develops, thus rendering fruit unfit for use. The 

 principal injury, however, is due to the destruction of shoots and leaves, 

 the latter frequently curling up when the insect clusters in dense 

 colonies upon the infested plant. The complete life-cycle has not been 

 followed under Xew Zealand conditions, but the shiny black eggs occur 



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