86 ' THE REPORT OF THE No. 36 



Another type of inter-relation is the galls seen on many plants, produced 

 by certain insects. The chief gall-producing families are the Cecidomyiidce 

 Trypetida.', Aphidida', Psyllida', CynipidcE and Tenthredinidce. Mites {Acarma) 

 also produce galls. Usually an egg is laid the growing tissue and the larva, 

 excites the surrounding tissue to abnormal growth. The transformations occur 

 within the gall, and the adult escapes. 



Galls are of various forms, often characteristic of the insects producing 

 them. The nutiiitive cells lying next to the contained larva contain both sugar 

 and starch and appear to function as feeders for both the larva and the growing- 

 cells of the gall, as our fellow-member Dr. Cosens has most admirably shown 

 in his recent studies. 



Insectivorous Plants. 



Certain plants such as the sundew, Venus's fly-trap, pitcher-plant and bladder- 

 wort entrap small insects and feed upon them. These plants secrete digestive 

 fluids which convert the tissues of the captured insects into liquid food capable 

 of being absorbed. 



Bacteria, and Fungi. 



Many caterpillars die from bacterial diseases. Silk-worms, cabbage worms, 

 army worms, gypsy moth caterpillars, grasshoppers and tent caterpillars are 

 frequently killed by bacteria. Certain fungi also destroy insects. Cordyeeps 

 destroys white grubs, wireworms and many caterpillars; Empusa is often respon- 

 sible for the destruction of house flies, plant lice, grasshoppers, crickets and 

 caterpillars; and Sporofrichum kills many kinds of insects. Attempts have been 

 made to control chinch-bugs and grasshoppers by artificial cultures of Sporo- 

 trichum and Coccohacilhis, but only with partial success. 



i 



Insects as Carriers of Plant Diseases. 



Flea-beetles by eating holes in the leaves of potato permit the entrance 

 of the spores of Early Blight (Macrosponum solani) and consequent partial 

 destruction of the leaves. It has also been shown fairly conclusively that certain 

 aphids and other insects* act as carriers of Twig Blight {Bacillus amylovorus) 

 of apples and pears, and it is now believed that the Squash-bag (Anasa Iristis) 

 the Striped Cucumber Beetle {Diabrotica vittata), the Twelve-spotted Cucumber 

 Beetle (D. 12-punctata) , the Cucumber Flea Beetle {Epitrix cucumeris), the Melon 

 aphis (Aphis gossypii), and the 12-spotted Ladybeetle {Epilmlma horealis) fre- 

 quently inoculate the stems of cucurbits with the cucurbit wilt {Bacillus trachei- 

 philus). Again, the punctures made by the Plum curculio in plum, cherry, and 

 peach permit the entrance of the spores of the Brown Rot disease {Sclerotinia 

 fructigema). Tree crickets {Oecanthvs spp.) are said to be responsible for the 

 inoculation of trees and shrubs with canker, of raspberries with the Cane Blight, 

 and probably for the production of other diseases. 



Inter-relations of Plants and Insects in Nature. 



The idea of inter-relations in Nature was first emphasized by Sprengel, 



Darwin and Miiller. and later ecological studies reveal still more clearly how 



— — — 1 



♦Gossard mentions among others Aphis avenw. Empoasca viali, Eccoptogaater rugu- 

 losus, and Lygus pratensis. " Any sucking insect can become a carrier, also any insect 

 with the bark^burrowing habit." 



