176 PROTECTION AGAINST INSECTS. 



every 10 yards along their floor. They cost IJd. to 2d. a 

 meter, or about 12s. per acre enclosed. The trenches must be 

 inspected every morning, and the insects which have been 

 caught should be killed. 



(c) Greased barriers. A line of barked poles, covered with 

 grease, is made, so as to exclude affected woods from sur- 

 'rounding hitherto immune woodlands,- or to enclose small 

 areas of unaffected woods. This method is applicable only 

 for larvae that come down to the ground. 



(d) Swine may be driven into woods which are attacked, and 

 they kill numbers of larvae and pupae which are in the soil- 

 covering. The swine must be given other food and driven 

 daily to water. As a rule, they eat only hairless larvae (Noctua 

 piniperda, Panz., Geomctra p iniaria, L.). 



(e) Pulling-up plants and burning shoots which have been 

 attacked ; or buds attacked may be pruned off. Infested 

 branches should be cut off. 



Stems full of insects, or their eggs, etc., may be cut down 

 and barked, and the bark burned or exposed to the sun. This 

 should be done before the perfect insects emerge, usually in 

 May and June. Great care must be taken as to the proper 

 season for barking such trees, which form so many tree traps. 

 If it be done too soon, before the bark-beetles have finished 

 breeding, there is danger of other standing trees being attacked, 

 and if it be done too late, after the perfect insects have forced 

 their way out and flown away, then the very institution of 

 tree-traps will have multiplied instead of diminishing the 

 numbers of the insects. It is therefore better to bark the 

 traps before the larvae have pupated, and to be informed when 

 this happens, infected trees should be observed, about every 

 14 days, in order that the development of the larvae may be 

 known and the right moment chosen for destroying them. 



(f) Preparation of tree-traps. Trees may be specially girdled 

 to serve as traps before the eggs are laid. For such purposes 

 stunted or sickly trees should be selected as for thinning 

 purposes. After the insects have visited them they should be 

 treated like trees attacked in the natural course. 



(g) Grease bands made of various substances such as tar, 

 glue, and grease, may be painted on trees, about chest high, 



