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THE INFLUENCE OF METEOROLOGICAL CONDITIONS 



UPON INSECT LIFE. 



By Robert Adkin, F.E.S. 



Mr. White suggests, in his notes on this subject (Entom. 

 vol. xxi. p. 217), that the influence of irregular or intermittent 

 temperature upon the emergence of insects has received less 

 attention than it deserves. No doubt this is so, and probably 

 one great reason for such being the case is the difficulty of 

 obtaining reliable data to woik upon. Accurate meteorological 

 records, it is true, are accessible in a conveniently tabulated form 

 for reference, not only temperatures, but also the amount of sun- 

 shine, rainfall and other matters calculated to affect insect deve- 

 lopment being given in detail. But can we place equal reliance 

 upon our entomological observations ? Are there not many other 

 conditions, besides those meteorological, that may escape our ob- 

 servation and yet have an important bearing upon the question ? 

 Notes of emergence in our breeding-cages, for instance, 

 appear to me likely to be particularly misleading. The con- 

 ditions under which insects are so kept, are to a greater or less 

 extent artificial. This is especially so in the case of sub- 

 terranean pupte. In nature these are surrounded by a consider- 

 able body of earth, which serves as a natural protection against 

 rapid changes of temperature, whereas under the artificial condi- 

 tions of the usual breeding-cage they have at best but a few square 

 inches of soil around them. Further, given, as is frequently the 

 case, that this soil is contained in a porous earthen pan, which 

 from any cause has become moistened, it is probable that a 

 refrigeratory action would be set up by evaporation, which would 

 create an abnormally low temperature in the interior of the 

 vessel containing the pupae, possibly resulting in late emergences 

 from purely artificial causes. As an example I will give the 

 following tabulated statement of the behaviour of three con- 

 secutive broods of Ptilophora plumigera, a species that performs 

 the whole of its metamorphoses during what are usually the 

 warmer months of the year. They were reared under as nearly 

 as possible similar conditions ; the cages containing them being 

 kept in a well-lighted outhouse, fully exposed to the air, but 

 sheltered from rain : — 



1886. 



Ova hatched April 26. 



Larvee full-fed May 28. 



First imago emerged... Oct. 9. 



Chief emergence ... Oct. 24. 



Last emergence Nov. 21. 



Assuming for the sake of argument that warm seasons induce 

 early emergences, we should expect to find the appearance of 



