GREENHOUSE PLANTS INSECTS 135 



pound to I gallon of warm water, is efficient for 

 those species on palms, ficus and similar plants; it 

 is unsafe on ferns ; fir-tree oil, i part to 20 parts of 

 water, is useful for the species on ferns ; fumigation 

 with hydrocyanic acid gas is most effective for the 

 mealy bugs; one should consult Farmers' Bulletin 

 880 of the U. S. Dept. Agr. 



The red spider ^" (Tetranyclius felarius) 

 Order — Acarina 



This pest has been discussed at length under pests 

 of cotton ; in greenhouses it attacks the rose, violet, 

 carnation, clematis, salvia, phlox, and other plants. 



Control — Washing plants with clear w^ater un- 

 der pressure is one of the best methods of control ; 

 ivory soap, ^ pound dissolved in 6 gallons of 

 water, is very satisfactory; nicotine sulphate plus 

 soap is also effective; fumigation with tobacco and 

 painting pipes with sulphur are not effective. 



The GREENHOUSE THRiPS ^^ (HeliofJirips ■ 

 hcemorrhoidalis) 

 Order — Thysanoptera 



The adult is a tiny, dark-brown insect only 1-24 

 of an inch in length; the young are whitish at first 

 but become reddish later; they extract the juices 

 from the leaves and the leaves become spotted and 

 covered with drops of. a reddish fluid excreted by 

 the insects; the eggs stuck in the leaves hatch in 8 

 days and the young become mature in 14 to 26 days. 



Control — Fumigation with nicotine papers or 

 with volatile nicotine extracts is effective if carried 

 on at night and repeated every week or ten days; 

 fumigation with hydrocyanic acid gas, i ounce so- 

 dium cyanide to 1000 cu. ft., for carnations for i 

 hour at a temperature of 54°, has been successful; 



12 Ewing— Oregon Expt. Stat, Bull. 121. 



13 Russell— U. S. Bii. Ent, Circ. 151. 



