142 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8 = 



determining the abundance or scarcity of insects as a whole than are 

 other natural checks such as parasitic and other enemies, or even 

 fungous or bacterial diseases " (p. 63). 



Recent studies have only crystallized long-held views to the effect 

 that the grand overwhelming factors of insect control are climatic.' 

 Thus Uvarov in discussing " Weather and Climate in their Relation 

 to Insects," ^ says : 



Apart from the seasonal rhythm in the appearance and activities of insects, 

 there is a more or less strongly marked periodic fluctuation of a species from 

 year to year. Only relatively few insect pests are equally numerous and injurious 

 every year, while most of them are practically negligible, except in certain 

 years, when mass outbreaks occur. It would be out of place to discuss here 

 all the causes for these periodic fluctuations, but I would like to point out that 

 recent researches in this direction tend to throw some doubt on the commonly 

 accepted idea that the chief controlling factor is the parasites, since a number 

 of cases have become known in which the factors normally keeping an insect 

 species down are almost entirely of meteorological order. This has been ad- 

 mitted for the cotton boll weevil in America (Hunter and Pierce, 1912), for 

 the corn-borer in Europe (Thompson and Parker, 1928), for the almond sawfly 

 in Palestine (Bodenheimer, 1928), for the cotton seed bug in Egypt (Kirk- 

 patrick, 1923), for plague fleas in India (Hirst, Rogers), for vine-moths in 

 Europe (Stellwaag, 1925), and for some other notorious pests. 



Again Bodenheimer in answering ' the question " Welche Faktoren 

 regulieren die Individuenzahl einer Insektenart in der Natur ? " states 

 that parasites, predators, and scarcity of food, are rarely or only 

 secondarily of regulatory significance, but that climatic factors are 

 the real controlling influences. 



Accepting the great superiority of meteorological phenomena as 

 regulative factors we may make some inquiry as to the relative im- 

 portance of other controlling agencies. Diseases sometimes are 

 dramatically destructive, but they rarely have a steady regulatory 

 influence. 



Among parasitic and predacious organisms it must be presumed, 

 except for specific limiting factors, that their effectiveness as control 

 agencies will be more or less in keeping with their total numbers. 

 Thus we can deduce from a table such as that on page 9 that most 



^This statement has general validity, for insects are nine-tenths of the 

 terrestrial animals above the size of nematodes, and probably a large proportion 

 of the smaller animals, as well as part of the tenth of larger size are subject to 

 similar checks. 



'Uvarov, B. P., Conference of [ British | Empire meteorologists, 1929, Agri- 

 cultural Section, pp. 17-18. 



° Bodenheimer, F. S., Biol. Zentralbl., vol. 48, pp. 714-739, T928. 



