REPORT OF THE ENTOMOLOGIST AND BOTANIST 179 



SESSIONAL PAPER No. 16 



The above life history will show how complex and difficult to understand are the 

 habits of some of our injurious insects. The importance of this knowledge, however, 

 cannot be over-estimated ; for it is plain that, if the Hop Plant-louse passes the winter 

 in the egg form upon plum trees, by having no plum trees near the hop yard, the op- 

 portunities for the insect to increase in a certain district are much reduced, and, fur- 

 ther, that, if plum trees near hop yards are treated during the winter to destroy the 

 eggs, a very large proportion of the infestation can be wiped out. It has frequently 

 been noticed by farmers and others with what enormous rapidity the different kinds of 

 plant-lice sometimes increase. Dr. Wm. Saunders, in the annual report of the Ento- 

 mological Society of Ontario for 1878, refers to this matter as follows : — 



' Some idea may be formed of the numbers to which in a short time plant-lice 

 increase, from a calculation of Curtis, the celebrated English entomologist, who com- 

 puted that from one egg only there would be produced in seven generations, taking 

 thirty as the average of each brood, the enormous number of 729,000,000, so that, were 

 they all permitted to live, everything on the face of the earth would in a short time be 

 covered with them. Indeed, sometimes the possible rate of increase is even greater 

 than this. Dr. Fitch, the state entomologist of New York, ascertained by actual ex- 

 periment, that the wingless females of the Grain Aphis became mothers at three days 

 old, and thereafter produced four young ones every day, so that even in the short 

 space of twenty days the progeny of one specimen, if all were preserved from destruc- 

 tion, would number upwards of two millions.' 



Some of the useful facts derived from a knowledge of the life history of the Hop 

 Aphis, are that, as the eggs are laid upon plum trees and pass the winter there, it is 

 important not to allow wild or useless cultivated plums to grow round hop yards ; but, 

 if these trees are growing in the vicinity and it is impracticable to destroy them, the 

 value of treating these before the eggs hatch, or just at the time the young plant-lice 

 are hatching in May, with kerosene emulsion, or a whale-oil soap solution, is manifest. 

 As the males are only produced at one season of the year and this on the hop plants 

 after the females have migrated to plum trees, the utility is plainly shown of burning 

 up at once after the crop is picked all the vines and leaves of the hop plants. In this 

 Vv'ay, it is believed that so many of the males will be destroyed that there will not be 

 enough left to fertilize all the females which have ilown away to the plum trees. Al- 

 though plant-lice can produce young for a long time without the intervention of males, 

 when the time comes for the perfectly sexed females to be produced, the males are 

 necessary for the fertilization of the over-wintering eggs. 



As tliere are three broods produced upon plum trees subsequent to the hatching 

 of the eggs, it is not until comparatively late in the season that the plant lice appear 

 upon the hop vines. It is an important observation then to know exactly at what date 

 this migration from the plum trees to the hops takes place, because these insects are 

 exceptionally prolific and multiply with enormous rapidity as soon as they reach the 

 hops. Consequently the sooner the plants are sprayed to destroy the aphides the easier 

 that work will be accomplished and naturally at a much smaller loss of vitality to the 

 plants. In New York State the migration from the plum trees to the hops takes place 

 in the month of jVIay, so it is probable that this may also be expected about the end 

 of that month, or early in June, in southern Ontario. 



As to the best insecticide for controlling the Hop Aphis, there are several which 

 may be used. Kerosene emulsion diluted to as weak a wash as one part to twenty-five 

 of soft water, will kill the insects upon the foliage at the time they migrate to the 

 hop plants. This strength will not injure the leaves, which it is stated is the case with 

 stronger mixtures. To destroy the winter eggs on plum trees a much stronger mixture 

 . of the emulsion, viz., one to six, is necassary. Instead of the above, whale-oil soap, 

 one pound to six gallons of water, may be used on the hop vines. The remedy, however, 

 which is by far most generally used by hop growers in England, California and Bri- 

 tish Columbia, is the one which has been styled the 'English wash,' and is the Btan- 



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