301 



In dealing with outbreaks of S. calcarata on a large scale, the only 

 practical method is the cutting out and burning of more than 75 per 

 cent, of the worst affected trees, which should be done in winter 

 when the wood may be used for fuel. Dead trees are a menace only 

 in so far as they afford a breeding-ground for other harmful wood- 

 boring insects. If not finished during the winter, this work should 

 be completed by July to ensure the destruction of pupae and adults. 



In order to protect valuable ornamental trees in parks and gardens 

 a repellent wash to prevent oviposition should be used, the best 

 consisting of 1 gal. soft soap dissolved in 6 gals, saturated solution 

 of washing soda, 1 pint of carbolic acid being added and thoroughly 

 mixed ; enough lime slaked in 4 gals, water should be added to form 

 a thick whitewash and -} lb. Paris green should be mixed in thoroughly. 

 Young larvae burrowing in the cambium can be mechanically removed 

 by a sharp knife or bent wire, or carbon bisulphide may be sprayed 

 into the burrows by an atomizer, the holes being immediately lightly 

 sealed with putty. 



ToTHiLL (J.D.). The Meaning of Natural Control.— Proc. Entom. Soc. 

 Nova Scotia for 19 IS, Truro, February 1919, pp. 10-14. ^Received 



21st May 1919.] 



The influence of natural control in the case of a few well-known 

 insects is discussed. The factors of control are divided into two 

 classes, those that restrict an animal or plant to certain geographical 

 ranges, such as oceans, deserts, mountains, climate, etc., and those 

 that effect the increase or decrease of an organism within its natural 

 range ; the latter group comprise such factors as are dealt with in 

 the present paper. A table shows the chief of these as concerning 

 Lepidopterous insects. Parasites that limit insect abundance are 

 of various kinds and include protozoal and bacterial diseases, fungous 

 epidemics, Nematodes, predaceous mammals, birds and insects and 

 insect parasites. Typical instances are given of outbreaks of 

 Malacosoma disstria (forest tent caterpillar) and HypJiantria sp. 

 (fall webworm) and of the various factors that influence their control. 

 It is pointed out that insect parasites and predators occupv a somewhat 

 peculiar position in that they can ovei-take a numerically increasing 

 host and so have a regulative effect not possessed by any other factors. 

 They are also the only factors that can be manipulated by human 

 beings, and therein lies the possibility of preventing outbreaks of 

 certain injurious insects. The present outbreak of HypJiantria sp. in 

 Nova Scotia is undoubtedly due to a scarcity of the two chief parasites, 

 Varichaeta sp. and Limnerium sp., and might have been prevented by 

 the introduction of large numbers of these four or five years ago 

 from New Brunswick, where they could have been collected in large 

 numbers. In Alberta M. disstria has been occurring in great abun- 

 dance for three years and no parasite could be found in either larvae 

 or pupae during last year or the present year ; these outbreaks might 

 have been prevented by introducing about four years ago numbers 

 of Limnerium sp. or Blephari'peza sp. from either the Atlantic or 

 Pacific provinces , where they are abundant. Lepidosaphes idmi (oyster- 

 shell scale) is largely controlled in North America by a mite, Hemi- 

 sarcoptes. This scale reached British Columbia many years ago, but 



