290 Chemotroplc Respoiises of Insects 



bulb thermometer, for example, are of little comparative value, and could 

 not be obtained during the night. The most noteworthy features of the 

 experiments enumerated in the preceding pages may be summarised 

 as follows. 



1. The experiments were conducted during July and August 1918, 

 and for the most part during wet and apparently unfavourable climatic 

 conditions. 



2. The insects attracted consisted almost exclusively of Diptera. 

 With the exception of one or two examples of Vespa vulgaris, no Hymen- 

 optera responded. Rhynchota, Coleoptera and Neuroptera {sen. lat.) 

 were unrepresented. A small number of Noctuid Lepidoptera entered the 

 traps, but for the purpose of conducting experiments with such relatively 

 large insects, as many Lepidoptera, it would be necessary to slightly 

 alter the construction of the traps used in order to allow of greater 

 facilities for ingress. 



3. Beer, cane molasses, and mixtures of these two substances are 

 powerful chemotropic agents for various Diptera. Ethyl alcohol, in 

 various concentrations, exhibited little or no chemotropic properties 

 but with the addition of small amounts of butyric, valerianic or acetic 

 acids it exercised a powerful stimulus. Aqueous solutions of the above 

 acids were not attractive, the respective esters probably being the 

 attractive agents in each case. The remaining substances utilised in 

 these experiments were found to exhibit little or no positive chemo- 

 tropic properties. 



4. Out of considerably over 3000 Diptera attracted during the course 

 of these observations, by far the greater number pertained to one or 

 other of the five families Rhyphidae, Mycetophilidae, Sepsidae, Muscidae 

 and Anthomyidae. 



5. As a general rule members of both sexes of a species were attracted 

 irrespective of the chemotropic agent employed. In the majority of 

 instances males predominated over females, but in no case where the 

 number of individuals of a species attracted exceeded 20 was the dis- 

 proportion greater than 2-9 males to 1 female. 



6. Rhyphus punctatus, Hylemyia strigosa and Calliphora erythro- 

 cephala were the dominant species attracted. 



