Canadian Forcslnj Journal, Mai/, HihS 



1675 



f rom larvae or from oggs will know how 

 effective the parasites often are. 

 In the northern woods, under average 

 conditions, these insects cause an 

 immense annual mortality among 

 such pests as the fall webworm, 

 forest tent caterpillar, and spruce 

 budmoth. I'nder particularly favor- 

 able conditions these parasites may 

 so supplement the work of other 

 factors in control as to all but elim- 

 inate such an injurious insect as the 

 forest tent caterpillar from an area 

 as large as New Brunswick. 



Thus the actual killing value of 

 insect parasites is fully as great 

 as that of any of the various factors 

 making for numerical reduction of 

 injurious forest insects. It may be 

 noted, moreover, that the parasites, 

 and, to a lesser extent, the predacious 

 insects, are distinguished by having 

 a regulative value in control. When 

 the forest tent caterpillar, for instance, 

 is scarce in a district it is usually 

 true that the percentage of parasitism 

 is low; when such a caterpillar in- 

 creases so, as a rule, does the per- 

 centage of parasitism. Thus the 

 tendency of these organisms is to 

 keep their food supply neither ex- 

 ceedingly scarce nor overly plentiful. 



A Disturbed Balance 

 With this kaleidoscopic and neces- 

 sarily sketchy review of the more 

 important restraining influences upon 

 insect activity in the woods, we have 

 a clue to the causes of insect out- 

 breaks. Outbreaks result when for 

 some reason one or more of these 

 restraining influences have not come 

 into play. Probably more often than 

 not, the prime cause of an outbreak 

 is a lack of insect parasites before 

 the insect host concerned is notice- 

 ably abundant. When an. abundant 

 insect is suddenly eliminated by 

 clirriatic vagaries, or epidemic dis- 

 eases, or what not, over a compara- 

 tively large area such as Prince 

 Edward Island, the parasites are 

 also eliminated from the same area, 

 that is, they perish of starvation. 

 If into such a parasite-free area a few 

 moths be subsequently blown, their 

 progeny in a few years' time may 

 produce an outbreak. 



With a consideration of the nature 

 of an insect outbreak in mind it is 

 now possible perhaps to answer the 

 question as to whether or not any- 

 thing can be done in a practical 

 way to control, or better still to pre- 

 vent, insect outbreaks. Man is im- 

 ])olent to manipulate the vagaries 

 of weather or to do very much in the 

 way of starling epidemic diseases. 

 He can, however, and should to 

 the utmost of his ability encourage 

 and protect insectivorous birds. 

 Distributing Parasites 



Moreover, through a knowledge 

 of the insect parasites and insect 

 predators of given destructive species 

 throughout their geographical range, 

 he may in many cases discover that 

 certain of these parasitic or predatory 

 species present in one part of the 

 insect host's range are lacking in 

 another. By collecting, transporting 

 and colonizing such species, he may 

 help to check or may even prevent 

 outbreaks. Such operations must of 

 course be based upon careful study. 

 The Dominion Entomological Service, 

 has an unusually clear-cut case of 

 this kind under consideration at 

 present. The forest tent caterpillar 

 which ranges from coast to coast 

 through the Canadian forest regions 

 is at present comparatively uncom- 

 mon in most of this range. At 

 Sylvan Lake, Alberta, however, an 

 outbreak of the insect has been in 

 progress for some three years. Upon 

 investigation it was discovered that 

 none of the insec": parasites efTecting 

 this forest pest in other parts of the 

 country were operating there. It 

 is proposed that certain of these 

 parasites, know^n to be abundant 

 on the lower end of Vancouver Island, 

 be colonized at Svlvan Lake. 



WOOD MEAL MANUFACTURE 



The production of wood meal as a 

 foodstuff will soon be realized. A 

 factory for this purpose is connected 

 with the eastern army headquarti.^ 

 at Souvalki; there are two factories 

 using Steffen's method, and another 

 being built. The War Commit 

 for Cattle Food Substitutes controlls 

 the use of this meal. — German officar 

 renort. 



