﻿ON ECONOMIC ENTOMOLOGY. 34? 



Australia the termites build their earth heaps in long rows from north-west to 

 south-east, which corresponds with the direction of the prevailing wind. 



The sense of smell and the power of attraction exercised by smelling 

 substances play a most important part in insect life. J. Perez and F. Plateau 

 have made exhaustive researches into the power of attraction exercised by 

 flowers and their scents upon insects. And it must not be lost sight of here that 

 the two sexes find each other by the sense of smell. That fact has long ago 

 been turned to practical use for catching and destroying insects ; and in 

 particular, collectors have utilised scented liquids for such purposes. Since 1910 

 this method has been applied for the first time against the moths of the 

 grape-worms (Clysia ambiguella and Polyclirosis botrana) — see J. Dewitz. 17 

 Efforts have been and are being made to discover by empirical methods those 

 substances which exercise the most powerful attraction upon the organs of smell 

 of these moths, and in connection therewith one fact seems to stand out as of 

 great practical importance. According to Standfuss 34 the catching of insects by 

 artificial scents yields to the lepidopterologist the richest harvest of fertilised, 

 egg-laden females. We find here the reverse results to those obtained by 

 catching insects with artificial light-traps, and we are inclined to think that in 

 the same way as the females of different species only lay their eggs after they 

 have been feeding, these egg-laden females are tempted to fly to their doom by 

 the iufluence of some attractive scent similar to that of a favourite food of theirs 

 or of other stimulating substances. 



The influence of external and internal factors on the development and life 

 of insects. 



It is almost needless to re-affirm here the very powerful influence which 

 climatic and atmospheric conditions exercise upon insects. Yet how small is our 

 positive knowledge of the physiological processes and changes which are 

 continously proceeding in the organisation of growing and full-grown animals ! 

 It is quite clear that such influences must combine with the physiological 

 conditions existing at the time in the organism, and that such combinations of 

 external and internal factors are liable to produce the most varied results. If I 

 were to enter exhaustively into these questions I could only do so in a voluminous 

 work ; hence I must confine myself here to making a few observations. 



It is generally understood that a hot and dry summer has upon many insects — ■ 

 including the much dreaded grape-worm, C. ambiguella — a most destructive effect. 

 Generally it is assumed that the eggs and larvae dry up, and this is undoubtedly 

 true to a certain extent. But the heat alone may be sufficient to account for the 

 sudden decrease and destruction of insect pests. Some years ago I 12 was 

 experimenting in order to ascertain exactly at what temperature eggs and larvae 

 of insects die ; and further what physiological processes take place in connection 

 therewith. Eggs and larvae in different stages of development were, while 

 maintaining the necessary quantity of humidity, kept under various degrees of 

 heat and then safely stored away. The results of these experiments led me to 

 arrive at the following conclusions : 



" The degree of heat which here comes into question is fairly constant and, 

 which is specially interesting, somewhat low. Side by side with this, in 



