21 



mean time it will be well that as much local knowledge regarding in- 

 sect and other pests should be accumulated as possible. 



Before passing on to the more practical matters of how best to co,.e 

 with the attacks of scale insects, it will be well here to give a short 

 sketch of their life and development on Citrus trees. 



We are indepted to American entomologists for much of what tg 

 known of the life history of scale insects, ai d the general account given 

 below will give some idea of how carefully they have studied this group. 



It must be understood that there is great variation exhibited in the 

 life histories within the group, but the following account will give a 

 general idea of their life and development 



With very few exceptions, scale insects are derived from eggs, the ex- 

 ceptions being in a few cases where the young appear to have been pro 

 duced aliv« , that is to say they emerge irom their shells or envelo es at 

 the moment of birth, and so seem to have been born alive. The eggs 

 are minute oval bodies, of various colours When just hatched the 

 insect is very small, oval in outline, with a flattened body, and furnished 

 with three pairs of legs, a pair of antennae, and a delicate sucking ap- 

 partus, consisting of three or four long fine threads by which to extract 

 the juices of plants. 



Although the larvae of scale insects are very minute, it is possible to 

 make them out with the naked eye as they run over the leaves, twigs 

 and fruit. At this stage of their existence they are usually of a light 

 lemon colour, and present the more typical insect form, by possesing an 

 articulated head, thorax and abdomen. Very soon after hatching, ge- 

 nerally within two hours, they seek suitable places on the leaves or stems, 

 in which to bury their sucking threads, and having done this, they soon 

 increase in size. As soon as they have started to feed they begin to 

 secrete and throw out waxy thread like secretions or filaments from the 

 upper surface of their bodies, which go to form, along with the cist or 

 mouiten skin, the beginnings of a scald covering, which is gradually en- 

 larged by further supplies of waxy filaments, as the increasing size of 

 the insect requires. 



After the first month they present a remarkable change, losing their 

 ant ; nnae, legs and eyes, they are degraded to not much more than a 

 mere sucking apparatus, appearing something like a sack possessed of 

 a beak-like process by which they adhere to the leaf or stem of the tree, 

 and through which they draw up its juices. 



The females cast their skins twice, and soon after the second 

 skin is cast they arrive at maturity. At the second moult the males 

 reach the pupal or chrysalis state, and unlike the females, they under- 

 go a complete metamorphosis, emerging from the pupa as minute 

 two-winged flies, possessed of eye*, antennae, and three pairs of legs, 

 but without mouth-parts. Their only function in life is to effect the 

 fertilisation of the females, which being done, the latter become dis- 

 tended with eggs, which are laid beneath the scale, and the body of 

 the female gradually shrivels up to make room for the eggs. 



General Observations. 



In tropical and sub-tropical countries where citrus trees are culti- 

 vated, scale insects are more or less active all the year round. In the 

 United States it has been observed that they produce three or four 



