Observations on the Life History of Taphrocerus gracilis 11 



and continued until the sun was well up in the sky and the temperature 

 had risen to 24° C. The time is not given, for the beetles were tested as 

 they were found by searching about among the bulrushes. 



It is to be noted from table 2 that there was a gradual change of the 

 response until the beetles all responded by flying. July 7, 1917, was a windy 

 daj r and the bulrushes were being blown about, and in 46 experiments on 

 that day, 35 beetles responded bj r flying, 10 by clinging, and 19 by con- 

 tracting. In this case, the proportion that contracted was unusually 

 high, for the temperature varied from 27.5° C. at 10.15 a.m. to 30° C. 

 at noon. Of the 19 beetles that retracted their appendages, 6 first clung 

 to the leaves and had to be dislodged with the forceps when they fell. 



This change of response, correlated with a rising temperature, was so 

 marked that laboratory experiments were used to verify the field observa- 

 tions. The beetles were placed in a jar containing bulrushes and sur- 

 rounded by warm water. At a temperature of 30° C, they were very 

 active, responded positively to light, and when disturbed took to their 

 wings or clung tenaciously to anything that came in contact with them. 

 When cracked ice was substituted for the .warm water and the temperature 

 was lowered to 15° C, the beetles became much less active and responded 

 negatively to light, which resulted in their retirement to secluded places 

 such as the crevices in the axils of the leaves; and when disturbed, they 

 retracted their appendages and allowed themselves to fall instead of taking 

 to their wings as with the higher temperature. 



correlation of structure and habits 



From the field observations and the laboratory experiments described 

 in the preceding paragraphs, one may correlate the retractile appendages 

 of the beetles with their reactions. When the temperature is low, and the 

 inactive beetles, by reason of their negative reaction to light, are at the 

 base of the leaf, any disturbance will cause them to retract their appen- 

 dages and fall into the crevice between the leaf and the stem. Attempts 

 to remove a beetle will only serve to push the leaf sheath away from the 

 stalk of the plant and allow the smooth, flat body of the beetle to slide 

 farther down into the crevice. 



On warm, sunny days the active beetles are out on the foliage, in accord- 

 ance with their positive response to light. When disturbed, they take to 

 their wings and escape, whereas if they responded as they do in a low 

 temperature, they would in many cases fall into the water. 



The abdominal prolegs, or ambulatory ampullae, 2 of the larva may be 

 considered as a structure correlated with its habits. Unlike its wood- 

 boring ancestors, the larva of this species crawls about in a mine between 

 the upper and lower layers of the leaf epidermis. The mine, as previously 

 stated, often appears as a blister with a spacious interior, in which the larva 

 would be unable to move about without some organ of locomotion. 



A model of the posterior end of the abdomen was made, in order to 

 determine what modifications have taken place in the development of 

 this apparently new structure. As shown by the drawings (Plates III 

 and IV), which represent, respectively, the right side and a part of the 



2 Ambulatory ampullae is the name given by Craighead (1915) to somewhat analogous structures on 

 cerambycid larvae. 



