NO. 9 OLFACTORY SENSE OF INSECTS McINDOO 3I 



drew its antennae through its mouth. The reaction to turpentine and 

 acetic acid was more violent. Next he cut otT the antennae. On the 

 second day after the operation he re{)eated the experiments, l)ut the 

 insects failed to res])ond to any one of these three strong odors. After 

 the operation the beetles ate with a greater appetite and some of them 

 lived more than two months thereafter. From these experiments 

 he concludes that the beetles lost the olfactory sense by the removal 

 of the antennae. 



Experiments with species of several other genera gave the same 

 results but those with beetles of the genera Carabus, Mclolontha, and 

 Silpha were less satisfactory. These never completely failed to re- 

 spond to strong-smelling; substances. If they are exposed for a long 

 time to the odors the insects deprived of their antennse become restless 

 and walk away from the glass rod, yet all the movements are less 

 energetic. The entire reaction is indefinite and weakened. Experi- 

 ments with Hemiptera gave a still less favorable result. After the 

 loss of the antennae these insects reacted almost as well as they did 

 with their antennae intact. 



Hauser performed the following experiments to ascertain the 

 value of the antenna in the search for food. He placed beetles 

 (Silpha) in a large box whose bottom was covered with moss. In 

 one corner of the box he put a small glass with a small opening, 

 the glass containing foul meat. As long as the insects possessed 

 their antennas they regularly found the meat in the glass after some 

 time, while after the removal of the antennae they never came in 

 contact with it. Similar experiments were performed with flies of 

 three genera. A vessel containing spoiled meat was placed on a 

 table by an open window. Soon several flies came to the meat. Then 

 he closed the window and cut otif the antennae at the third joint. 

 Thereafter not one of these flies came in contact with this meat. 



Hauser next ascertained the value of the antennae to the male in 

 finding the females. Male and female beetles and butterflies were 

 placed in large boxes. As long as they were normal in every respect 

 they mated freely, but when the antennae were cut ofi^ they copulated 

 only occasionally. 



Hauser, who worked extensively and thoroughly on the antennae 

 of insects of all orders, found many difl^erences in the various orders 

 but among dift'erent Hymenoptera the differences in distribution and 

 structure of the antennal organs are comparatively slight. Accord- 

 ing to him, Vespa (a wasp) possesses about three times as many pegs 

 as does the honey bee, and for this reason J'^cspa has better olfactory 



