CHAP. X.] [NSECT PESTS. 77 



of food being the main checks on its increase; climate per se may 

 be neglected, for it may be assumed that an insect living under 

 natural conditions is adapted to the climate of the locality in which 

 it lives. Taking as an example a moth which depends for its 

 existence upon a wild jungle plant, its eggs may be parasitized before 

 they hatch or may be discovered and eaten by sonic predaceous 

 enemy, such as an ant; the caterpillars are also liable to be para- 

 sitized or carried off by birds, wasps, ants or other predators before 

 they have finished feeding and, if too many eggs have been laid on 

 tin- one plant, they may starve or be exposed to special dangers 

 whilst wandering in search of more food ; when full-fed, many 

 caterpillars leave the fond-plant and descend to the ground to 

 pupate and at sue!; times they are especially liable to attack by 

 ants and predaceous birds and insects, whilst even after pupation 

 they may be dug out and devoured by birds such as Hoopoi 

 burrowing mammals or insects ; finally, when the insect has survived 

 all these dangers and emerged as a moth, it has not only to feed 

 but to search out scattered plants on which to lay its eggs and at 

 this time especially a slow-flying egg-laden female is a special mark 

 for attack by birds and other enemies. On the other hand an i' 

 which feeds on a cultivated crop is spared many of these dangers. 

 The crop is generally grown closely and therefore of itself provides 

 a certain measure of shady security, so that pre ! I parasites 



are at an initial disadvantage, whilst the influence of dry, hot winds 

 or other climatic factors is reduced to a minimum both as regards 

 the direct effect on the insect and indirectly as reducing the avail- 

 able moisture in the foodplants. There is no lack of food and this 

 fact consequently eliminates all necessity for searching for another 

 plant when one has been eaten up, whilst the adult female insect 

 also is practically exempted from danger in searching for the 

 requisite foodplants on which to lay ! 



The destruction of forests and other alterations of natural features 

 at tin- hand lit man have far-reaching and often quite unforeseen 

 influences on the flora and fauna of the areas affected. An imme- 

 diate effect is often the washing away by rain of the soil which is 

 the accumulation of the natural decay of vegetation during probably 

 thousands of years and which has hitherto acted like a vast sponge 

 tain a stable condition of moisture throughout the year, so that 

 the climate of the disafforested area tends to become less equable. 

 After some time a secondary jungle may spring up. or very often the 

 land is placed under a crop, but the old condition of things has been 

 irretrievably altered and many plants and animals which lived in 

 the forest are unable to adapt themselves to the altered conditions 

 and die out. The interrelations between various if animals 



