﻿ON ECONOMIC ENTOMOLOGY. 345 



Gastine 21 and myself it is, however, permissible to conclude that the colder the 

 night the fewer the females (and, in particular, females with eggs) that are 

 caught by acetylene trap-lamps. Strange occurrences may be observed in this 

 respect. Of Porthesia chrysorrhoea not many specimens were generally caught 

 and rarely indeed females ; but then followed nights when very many specimens 

 were caught, and amongst them also some females. Altogether I caught during 

 such experiments 940 specimens of Porthesia of which only 24 were females. 

 Strange to say, nine catches, yielding altogether 562 specimens (averaging 62*4 

 specimens per catch) furnished me with 24 females, whereas 94 catches yielding 

 in all 378 specimens (averaging only four specimens per catch) did not supply 

 one single female. Hence one may conclude from such results that there exist 

 in the atmosphere peculiar conditions, so far unknown to science, which affect the 

 flying tendency of insects during night time according to their sex. 



I will mention here a case of phototropism which has been investigated by 

 E. Molz. 29 The experiments were carried out for the purpose of ascertaining 

 the reason of the well known fact that some insect larvae invariably rest on the 

 upper side of leaves, while others seek the lower side. The larva investigated 

 was that of Eriocampa adumbrata, which lives on leaves of the cherry tree. It 

 was found that these larvae always endeavour to orient themselves so that the 

 rays of light fall vertically upon their backs ; hence, under natural conditions, 

 they are only found on the upper surface of the leaf. 



I can only hint here at some of the effects of phototropism on insects and 

 their larvae ; how it dominates their choice of location ; how it forces them now 

 to live in full light and at other times under quite opposite surroundings, in order 

 to perform their metamorphoses ; how it causes some to go in search of food 

 during the day, others during the night. All these varying conditions are of the 

 utmost importance for the study of the life and destruction of injurious insects 

 and should in their various bearings be brought under one common physio- 

 logical aspect. We may, therefore, do well to bear in mind here that recently 

 Oswald 30 has connected phototropism of animals with certain enzymes which are 

 found in them. According to him photo tropic reactions are intimately connec- 

 ted with the respiratory action of the tissues. Positively phototropic animals 

 are rich in catalase and poor in peroxydase, whereas with negatively phototropic 

 animals the reverse conditions prevail. 



Reaction to contact or stereotropism is widely distributed amongst the lower 

 animals, and the mode of living and conduct of many species can be traced back 

 to it. With animal spermatozoa, which possess this attribute in a high degree, 

 it is perceptible, as Massart 28 and I 4 have demonstrated, in their desire either to 

 attach themselves closely to solid substances or to penetrate into porous ones ; 

 and similar reactions may be observed in the behaviour of snails, earth-worms, 

 nematode worms and other lower animals, which dispose themselves in response 

 to this stimulus. Insects and their larvae endeavour to fasten their bodies 

 tightly to corners or to sharp and prominent objects, or to squeeze themselves 

 between layers of folded dry goods. On these facts is based the employment 

 of belts round fruit trees in order to catch the larvae of Laspeyresia ( Carpocapsa) 

 pomonella ; also the use of paper bands or cloth strips for catching the caterpillars of 

 the Tortricidae of the vine ; likewise the use of flat stones or wooden boards in 



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