12 BULLETIN 104, TJ. S. DEPARTMENT OF AGRICULTURE. 
August 19, 1912. — All spikes examined. 
Nos. 1, 2, and 3 in good condition; no signs of thrips or other insects; no injury 
from nicofume; good seed formed. 
No. 4. No injury from nicofume apparent; no evidence of thrips or other insects; 
emasculated July 24, 1912; pollinated July 27, 1912; of 10 flowers pollinated 8 pro- 
duced seed. 
No. 5. General condition similar to No. 4; emasculated July 24, 1912; not polli- 
nated; 13 flowers emasculated; all remained sterile. 
No. 6. Similar to No. 5; all flowers remained sterile. 
No. 7. Check; spike dead. 
This experiment shows that the treatment with nicotine solution 
did not perceptibly injure beet flowers and that it at the same time 
removed thrips from them. 
CONCLUSION. 
From these experiments it is seen that these minute insects, the 
numerous species of Thysanoptera, some of which more or less injuri- 
ously infest practically all our plants, are also active agents in pol- 
lination. Among beet flowers they are frequently very numerous 
indeed, effecting both close pollination and cross-pollination upon 
them. However, after taking into account the various forms of 
injury they do, it is doubtful whether the balance remains in their 
favor in regard even to beets. Under ordinary conditions, in fields 
of commercial seed beets, it is believed that on the whole their work 
is beneficial; but should they become excessively numerous, they 
sustain their reputation as one of our really destructive pests. To 
the horticulturist and plant breeder they are pests of the worst type, 
necessitating constant watchfulness and a refined technic in all 
pollination work. 
The suggestion is ventured that certain supposed mutations may 
really have been the result of unsuspected cross-pollination by means 
of one or another species of thrips, whether in cereals supposedly 
not susceptible to cross-pollination without the intervention of man 
or in flowers which were thought to have been isolated against 
cross-pollination. 
o 
WASHINGTON : GOVERNMENT PRINTING OFFICE : 1914 
