February, '17] HEWITT: INSECT BEHAVIOUR 85 



gations of Howlett on the fruit-flies of the genus Dacus in which the 

 males are attracted by the eugonol oils, iso- and methjd-eugonol, which 

 are constituents of oil of citronella. 



The control of outbreaks of the larvae of Arctiid moths in India by 

 the captm-e of the adult moths in bait traps of the Andres-Maire 

 pattern is an example of the manner in which practical advantage 

 may , be taken on a large scale of a chemotropic response. 



The negative chemotropic reaction of insects is illustrated in the 

 practical use of repellent odors. Musca domestica is repelled by certain 

 coal-tar products such as phenol; the protection of cattle from biting 

 flies and of man from mosquitoes is secured by the use of repellent 

 mixtures. 



Turning now to a problem of great biological interest and practical 

 importance, namely, the different behaviour of the same species of 

 insect to difl'erent plants, we find that what would appear to be funda- 

 mentally a chemotropic reaction is sometimes responsible for the 

 creation of a biologically different race of the same species. In his 

 investigations on blueberry insects in Maine, Wood has found a form 

 of Rhagoletis pomonella infesting blueberries {Vaccinium) and huckle- 

 berries {Gaylusaccia baccata) that is below normal size, and this form 

 appears to be long-established as efforts to get the apple-bred race to 

 oviposit on blueberry and vice versa, failed. The physiological influence 

 of the host plant upon the insect feeding upon it and the creation of 

 biologically different races which may differ sufficiently to be separated 

 as species by the tendency of members of a single polyphagous species 

 of insect to become adapted to a particular food plant is strongly 

 suggested by Cameron's study, of the leaf-miner Pego?nyia hyoscyami 

 Panz. which feeds on belladonna (Atropa belladonna). Within this 

 category we should also include, I believe, the case of the Arizona wild 

 cotton weevil (Anthonomus grandis thurbericv Pierce). The production 

 of morphological changes by a change in food plants has been observed 

 in like manner in the case of Aphides. These chemotropic responses, 

 for that is essentially their nature, have as important a relation to 

 the work of the taxonomist as to that of the applied entomologist. 



A subject which promises results of great practical value is the study 

 of the resistance of plants to insect attack with a view to the produc- 

 tion of insect-resisting varieties in crops subject to injury. Com- 

 paratively little attention has been paid to this further example of 

 chemotropic reaction, but the development of strains or varieties com- 

 pletely or even partially resistant to the attacks of particular insects 

 attacking them, would place a valuable preventive measure in our 

 hands. This is a field for joint investigation by the entomologist and 

 the plant-breeder. 



