354 GROWTH OF PLANTS 



Plant products. A survey of plant products for insecticidal properties 

 has resulted in testing some 300 species and varieties of plants on mosquito 

 larvae {Culex quinquefasciatus Say). As mosquito larvae are relatively easy 

 to kill with insecticides, any substance that shows promise is likely to be 

 detected. Another advantage of mosquito larvae as test insects is that 

 they may be tested in an aqueous solution, thus insuring proper wetting 

 rather than having the spray atomized on the body of the insect, which 

 results in a variable coating even under the most precise conditions of 

 spraying. Both acetone and water extracts have been made of all the plant 

 products tested. Usually the products are tested at several concentrations. 

 Mosquito larvae tests are made at a temperature of 29° ± 1° C (84° ± 2° F) 

 for periods of 16 hours, following a standard method.^''' ^^ 



The median lethal dose (LD50) for mosquito larvae for balm of Gilead 

 {Populus sp.) buds was found to be 5.8 ppm,^^ for filicin, a product of male 

 fern (Aspidium filix-mas [L.] Sw.) 11 ppm,^^ for echinacea {Brauneria sp.) 

 root 16.5 ppm, for sage (Salvia officinalis L.) root 18.3 ppm,^^ for cubeb 

 (Piper cuheha) berries 25 ppm, for oil of sweet basil 28 ppm, for black 

 ' pepper (Piper nigrum) 29 ppm,io for oil of cypress 31 ppm, and for oil of 

 rosemary 78 ppm. In comparison the LD50 for mosquito larvae for the 

 isolated toxin rotenone is 0.06 ppm.^^ 



The fact that a plant extract is toxic to mosquito larvae does not neces- 

 sarily indicate that it possesses toxicity to other species of insects. An 

 acetone extract of balm of Gilead buds is very toxic to mosquito larvae but 

 possesses little or no toxicity to Aphis rumicis; on the other hand, filicin 

 possesses a toxicity comparable with pyrethrum to mosquito larvae, Aphis 

 rumicis, and houseflies. Satisfactory kills were obtained with Mexican bean 

 beetle (Epilachna varivestis Muls.) when bean plants were dusted with 

 black pepper and the adults allowed to feed on the foliage.^" The toxicity 

 of piperine, a product of black pepper, was discussed in the previous 



section. 



Synthetic products. The need for synthetic compounds as insecticides 

 has become very acute due to the shortage of natural products such as 

 pyrethrum and rotenone-containing plants as the result of the war. An 

 example of this type of research is the recently published paper by Harvill 

 and Arthur ^^ on the allyl phenols as fly sprays. AUyl phenols were found 

 to possess insecticidal properties. The median lethal dose of o-allylphenol, 

 o,o'-diallylphenol, and o,o',p-triallylphenol was 18.5, 10.5, and 2.63 per 

 cent respectively. 



The 7-thiocyanopropyl and /S-thiocyanoethyl esters of phenols were 

 found to be very toxic to houseflies and had a very rapid paralyzing effect. 

 Likewise, the T-thiocyanopropyl ether of 1,3,5-xylenol was found to be an 

 excellent fly spray because of its high toxicity, rapid paralyzing effect, 

 and lack of objectionable odor. 



