DAMAGE CAUSED BY ANIMALS. 117 



pupal stage before succumbing from the effects of the attacks. 

 Whether or not any caterpillar has become infected may, in 

 the case of hairless and brightly-coloured caterpillars, be told by 

 the appearance of dark punctures where the eggs have been 

 deposited, but in other cases only by making sections to see 

 if any larvse have developed themselves. 



The importance of the role played by ichneumon-flies during 

 insect calamities has occasionally been over-estimated, occasionally 

 under-estimated. It is perhaps correct to say that they of them- 

 selves will never be able to suppress totally any serious devasta- 

 tion of woodlands caused by the voracity of swarms of caterpillars, 

 as the extent to which their reproduction can take place is 

 dependent on the presence of a still larger number of caterpillars ; 

 but, at the same time, it is certain that they contribute very 

 materially to reduce and shorten the calamity. If sections made 

 prove that a large number of caterpillars have been infected 

 with ichneumon parasites, it may be taken for granted that the 

 calamity is approaching its end, 1 and any direct destruction of the 

 caterpillars need no longer take place, as that would involve the 

 killing of a much greater number of useful allies among the 

 Ichneumonidse. 



60. Preventive Measures in general. 



In view of the extreme difficulty, and sometimes almost the 

 impossibility, of annihilating and exterminating injurious insects 

 when once they have obtained a footing in large numbers, it should 

 be the special care of the forester and the sylviculturist in the first 

 instance to prevent their numerical increase taking place on any 

 very considerable scale: PRINCIPIIS OBSTA must be a motto 

 never lost sight of. 



To begin with, he requires above all some knowledge of the 

 appearance, habits, and life-history of injurious insects ; and at the 

 same time, he must from time to time make a careful examination 

 of the woods, paying particular attention to all windfall areas, to 

 recently felled coniferous timber lying stacked for sale or removal, 

 and to all sickly plantations and backward crops, which may de- 



1 Experience of past calamities has shown that under such circumstances fungoid 

 diseases also break out largely among the caterpillars, such as that occasioned by 

 species of Botrytis (which also causes Muscardine in silkworms), Isaria, Cordiceps, 

 Micrococcus, Bacterium, Sacharomyces, and Torula. Trans. 



