1920 ENTOMOLOGICAL SOCIETY. 19 



EXPEKIMENT OF ChLOROPICKIN ON PLANTS IN A GREENHOUSE.. 



Capacity of greenhouse, 675 cubic feet approximately. Temperature in the 

 house (June) 90° F. Ten cubic centimetres of gas were used in each of three petri 

 dishes, two in opposite corners of the room on a table, and one on the floor. The 

 nearest dish was right amongst the plants, which were : Recently potted dandelion in 

 flower, Michaelmas daisy, wild vetch and curled dock, a geranium in a pot and cut 

 boughs of willow. Insects present: Thrips, geometrid larvae, leaf -rollers, Cer- 

 copidae, immature Jassidae and some Muscidae flying around the room. 



A gas mask was used throughout the experiment in order to observe the action 

 of the gas on the insects. 



The leaf-hoppers were the first to show signs of distress by falling off the 

 willow boughs six minutes after the gas was introduced. At the end of 10 minutes 

 and 20 minutes respectively 10 cubic centimetres more of gas were poured out, 

 this time on the floor making a total concentration of 50 c.c. After an exposure' 

 of 23 minutes the thrips were apparently all dead, although they had fallen out 

 of the flowers after 11 minutes. At this time the Jassids and the immature 

 Cercopids whose spittle masses, had not been disturbed at all were also on the table 

 moving feebly. 



The experiment terminated in 38 minutes with the thrips, Jassids and 

 Muscids all dead and the cercopids, the geometrid and leaf rollers very feebly 

 moving. The doors and windows were opened and kept open until the house could 

 be freely entered without discomfort, the gas being dispelled in 5 minutes. Next 

 morning, i.e. after 17 hours those insects which had been feebly moving the day 

 before were all dead. The cercopids alone, in untouched masses of spittle, were 

 apparently unharmed. But all the plants were drooping badly, Especially the 

 vetch and michaelmas daisy, and at the same hour the second day, all the plants 

 were dead. ' 



In this experiment the temperature was very high and the relative humidity 

 must have been high also as the floor of the house had been recently watered. 

 But the volume of gas was very low, being for half the experiment only 30 c.c. 

 and at the end of the experiment only 50 c.c. per 675 cubic feet, which amounts to 

 only 3.7 oz. per 1,000 cubic feet. 



With these results in mind, the following experiments were carried out at 

 Guelph, the relative humidity being determined in each case: 



1. Varying strengths of gas — other factors being equal. 



2. Shorter or longer period of exposure. 



3. Exposure by night and by day. 



4. The killing power of the gas on various insects. 



A good supply of Eed Spider on salvia and of mealy bugs on coleus was avail- 

 able in the greenhouses of the College and as both these host plants show great 

 susceptibility to killing by hydrocyanic gas, it was considered advisable to try 

 the comparative value of chloropicrin on them. 



Experiments were conducted at first in daylight, and proved that exposure 

 to an atmosphere at the rate of 3 pounds of gas per 1,000 cubic feet, relative 

 humidity 87, temperature 55.8° F. kill red spider effectively in 8 minutes — but 

 kill salvia host plants in 5 minutes. And while 40 minutes exposure kill^ coleus 

 and begonia, it does not kill all the mealy bug; those with their mouth-parts 

 inserted in the stem of the plant seeming to survive those that were moving about. 

 By next day young were issuing freely from the egg masses. 



