SPRAY RESISTANT INSECTS.

Dominion, Volume 7, Issue 1874, 7 October 1913, Page 10

SPRAY RESISTANT INSECTS.

Something of a sensation has been produced among Californian fruit-grow-ers by tho suggestion of the Principal of Entomology of tho Washington Stat© Collego that possibly under continued spraying with insecticides hardier strains of insect pests aro being produced, which aro better and better able to withstand .tho effects of the 'poisons. "In other words," said Professor Melander in his address, "it is possible from a biological standpoint that we aro breeding tho resistant insects. If there is such a thing as this, it is a big, big thing in the fruit world. A few years ago we wore cocksure that sulpliur-limo would kill red spider eggs, would kill eggs of the green aphis, and yet I havo examined I don't know how many millions. of red spider eggs this year, and failed to find them dead after being 6prayed with sulphur-lime. The samo can be said of tho green aphis in a good many localities. Whether it is a biological fact that scalo and other j insects are becoming resistant by a

gradual process of weeding out tho individuals that aro not hardy I do not know; but I do know that somo of the standard sprays are not nearly so sure and effective as the.y used to be. That is tho main thing that I wanted to surprise you with at this ' time. If the biological theory is true, that wo are breeding up scales that aro resistant to this or that spray, it may bo that we shall have to switch our methods of fighting tho pests, we will say, every 20 years. We will spray with sulphurlime—that will bo tho best for 20. years; and thou we will switch over and take up the oil emulsion and spray with that for 20 years until wo get a scale that is resistant to oil emulsion, and then come back and switeh to the other. Biologically it is possible to rear up a breed that would be resistant."

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