^21 



Imms (A. D.) & HrsAiN (M. A.). Field Experiments in the Chemotropic 

 Responses of Insects. — Ann. App. Biol., Cconbridge. vi, no. 4. 

 April 1920, pp. 269-292. 



The results of preliminary studies on the subject of chemotropism 

 in insects are described. A summary of the Hterature already published 

 on this question shows that previous observations have been directed 

 to finding out the responses of some particular species. The work 

 here discussed on the other*hand is quantitive in aim -^^th a view to- 

 obtaining the data on the attractiveness of various substances in 

 various conditions, their optimum attractive strength and relative 

 powers of attraction in relation to other substances, the species 

 attracted, their numbers and the proportion of the sexes, and meteoro- 

 logical data. 



The experiments were conducted during July and August 1918, 

 and for the most part during wet and apparently unfavourable 

 climatic conditions. The most noteworthy features of the investigation 

 may be summarised as follows. 



The insects attracted consisted almost exclusively of Diptera. 

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

 Hymenoptera responded. Rhynchota, Coleoptera and Xeuroptera 

 {sens, lat.) were unrepresented. A small number of Noctuid moths 

 entered the traps, but for the purpose of conducting experiments with 

 such relatively large insects, as are many Lepidoptera, it would be 

 necessary to alter slightly the construction of the traps used in order to 

 allow of greater facihties for ingress. 



Beer, sugar-cane molasses, and mixtures of these two substances are 

 powerful chemotropic agents for various Diptera. Ethvl 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 chemotropic 

 properties. 



Out of considerably over 3,000 Diptera attracted during the course 

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

 other of the five families Ehyphidae, Mycetophilidae, Sepsidae, 

 ^lusciDAE and Anthomyidae. 



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 

 disproportion greater than 2*9 males to 1 female. 



Rhyphus punctatus, Hylemyia strigosa and Calliphora erythrocephala 

 were the dominant species attracted. 



Havilaxd (M. D.). On the Sexual Forms of Aphis saliceti, Kaltenbach. 

 —Ann. App. Biol, Cambridge, vi, no. 4, April 1920, pp. 311-313. 



Of a number of Aphis saliceti, Kalt., collected on sallow {ScUix 

 caprea) in June 1919 the majority were foimd to be sexual males and 

 females, and not parthenogenetic indi\'iduals as might have been 

 expected. This has been observed before with regard to this species 



