NO. 10 TROPISMS OF LEPIDOPTERA — McINDOO I9 



III. GEOTAXIS 



I. REVIEW OF LITERATURE 



Frank in 1870, according to Mast (56, p. 12) , invented the term geo- 

 tropism to designate the reactions of parts of plants to gravity. Loeb 

 (42, p. 85 ; 43, p. 125) in 1888 claims to be the first to call attention 

 to the influence of gravity on the orientation of animals. Caterpillars 

 of Bomhyx neusfria were found to be geonegative, for, when confined 

 in a wooden vessel with the opening at the bottom, they crept upward. 

 Loeb says that " geotropism," like " heliotropism," is evident only at 

 certain epochs in the life of an animal, for the result of the geotactic 

 tests were not at all times consistent in the same animals. Loeb (42, 

 pp. 33, 44) confined caterpillars of Euproctis chrysorrhoea in test 

 tubes in a dark room and found them to be geonegative. He remarks 

 that strongly negative geotaxis is no isolated phenomenon in insects 

 at the hatching time and immediately after the adults have emerged 

 from the pupa cases. Caterpillars of butterflies, like freshly emerged 

 moths, are also geonegative, though not so markedly. Immediately 

 after emerging geotaxis is much stronger than phototaxis in the butter- 

 fly, but later these reactions are usually reversed. 



Mayer and Soule (59) found three species of caterpillars to be geo- 

 negative. Geonegative and photopositive reactions serve to maintain 

 the caterpillars of the milkweed butterfly near the upper part of their 

 food and to lessen the risk of their wandering down the stem and 

 starving before being able to find another milkweed. Two species of 

 moth caterpillars were geonegative when about to pupate, but they 

 always pupated head downward. 



Dewitz (9) remarks that geotaxis may frequently combine with 

 phototaxis, thereby forcing the animals to locate themselves on the 

 extreme ends of tree branches and on the crowns of trees (negative 

 geotaxis), or to descend into the soil (positive geotaxis). 



Lammert (40) used an electric light beneath a special apparatus and 

 found all the caterpillars tested to be geonegative with the light turned 

 ofif. When the stimuli from light and gravity were simultaneously 

 tested the light stimuli were the stronger. 



The latest paper known to the writer which deals with geotaxis in 

 insects is by Crozier and Stier (7). Their tests were conducted in a 

 ventilated dark room the temperature of which ranged from 21° to 

 24° C. A weak nondirective red light was used and the observer's 

 breathing currents were excluded by a screen. Tent caterpillars 

 {Malacosoma mnericana) were tested and each was caused to creep 

 diagonally across an inclined plane, which rested on a horizontal one. 



