Effects Produced by Sucking Insects and Red Spider Upon Potato Foliage.

1 Definite and similar symptoms apart from any other cause were obtained as the result of infesting young plants raised from seed of the President variety of potato with Red Spider, Aleurodes, Aphis, Jassid, and Capsid under various experimental conditions at Wisley and Chelsea as follows: (a) Red Spider.–Leaves became mottled, plant turns brown and dies. (b) Aleurodes.–Effect gradual, plants weakened but did not die, (c) Aphis.–Leaves with discoloured veins, brown and dead leaf-ends, yellowing and death of the plant. (d) Jassid.–White spots, plants did not die. (e) Capsid.–Dark brown blotches on leaves and young growth, veins darken, young leaves and shoots killed rapidly. These symptoms did not develop in the controls except in the cases where the control plant became infested by the particular insect experimented with. 2 The effect on the foliage tissue in each case is as follows: (a) Red Spider.–Epidermal and sub-epidermal cells injured. (b) Aleurodes.–Conducting tissue tapped, not followed by vein discoloration. (c) Aphis.–Conducting tissue tapped followed by vein discoloration after nine or ten days. (d) Jassid.–Epidermis punctured, assimilatory tissue destroyed. (e) Capsid.–Tissue lacerated causing severance of the veins and leaving ragged, irregular pits which become rapidly discoloured as do the veins also within two days. 3 The markings caused by Jassids and Capsids proved distinctive and could be recognised as such for some time after the injury, but for the safe recognition of Aphis injuries the association of typical markings with Aphides or their remains is necessary. 4 Evidence has been obtained that Aleurodes select plants. 5 Definite symptoms due to Aphis, Jassid and Capsid, correlated with the presence or remains of these insects, have been found in the field crops in several districts in three consecutive seasons. During and after periods of wet weather the original injur) >s, especially those caused by Aphis and Capsid, frequently obtain se ondary extension, and the foliage is prematurely destroyed. 6 From field observations Aphides appear to exhibit a preference for certain varieties or races of potato, but the question of selection has not been experimentally studied by us.