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THE Al^HIDES OR PLANT LICE. 



Bt W. Satjnders, London, Ont. 



Under the common term aphis or plant louse is embraced a number of distinct species 

 belongino; sometimes to different genera, but all resembling each other so closely in appear- 

 ance or habits as to lead to their being grouped under one common name. So closely do 

 many of the species resemble each other, that their distinguishing features cannot be made 

 out without the u.'^e of a magnifying lens. There are very few plants, shrubs, ornamental or 

 fruit trees, but are more or less affected by these insects, and on many of them they luxuriate 

 and thrive to such an extent as sometimes to threaten their destruction. These plant lice 

 are not restricted to any part of a plant ; often they are found on the leaves, but sometimea 

 on the stems, or again on the roots of plants, while other species roll up the leaves, or 

 form gall like swellings on them. This troublesome tribe of insects holds a position in regard 

 to the vegetable world, somewhat analogous to that of some well known parasites on animals; 

 hence the popular name plant lice. They belong also to the same great order of insects, 

 Hemiptera, all of whom obtain their livelihood in a similar manner, viz : by suction. Phey 

 are all furnished with a beak-like mouth, sometimes hard and solid, which is thrust into the 

 plant or animal they are feeding on, and used to extract its fluids. 



Plant lice are remarkable for their fecundity. People are often puzzled at finding their 

 plants or trees swarming with plant lice, where a week or two before there was scarcely one to 

 be found. As a general rule an aphis, during the summer season, reaches maturity in ten 

 or twelve days from birth, after which it produces every day two young ones, which, contrary 

 to the general rule with insects, are born alive. This rate of increase is maintained for a con- 

 siderable period, from fifteen to twenty d;iys or more ; the young begin to produce in like 

 manner in from eight to ten days, and so on through the third, fourth and sometimes up to 

 the twentieth generation in one season. Some idea may be formed of the numbers which in 

 a short time this rate of increase would produce, from a calculation of Curtis, a celebrated 

 English Entomologist, who has computed that, from one egg only, there would be produced 

 in seven generations, taking thirty as the average of each brood, the enormous number of 

 seven hundred and twenty-nine millions, so that were they all permitted to live, everything 

 on the face of the earth would in a short time be covered witii them. Indeed, sometimes the 

 possible rate of increase is even greater than this. Dr. Fitch, late State Entomologist of 

 New York, has ascertained by actual experiment that in the case of the grain aphis, the wing- 

 less females become motiiers at three days old, and thereafter produce four little ones every 

 day, so that even in the short spice of twenty days the progeny of one specimen, if all were 

 preserved from destruction, would number upwards of two millions. 



It may be urged in objection to these calculations, that no allowance is made for a cer- 

 tain percentage being males, but strange to say all through the summer there are no males 

 born, but all are fertile individuals, giving birth to others, and these to others still, inde- 

 pendent of any influence from the opposite. With m.my species, some individuals of each 

 brood acquire wings, while others arc wingless; the wingless ones remain, of course upon the 

 plant upon which they were produced, while the winged specimens fly to other plant.s, where 

 they establish new colonies. About the middle uf September, the last generation fur the year 

 is produced, which consists of males and females, the males generally becoming winged On 

 reaching maturity, the sexes pair, when the females no longer bring forth ymuig, but lay eggs, 

 which arc able to rcsi.st the severe cold of winter, and these hatching in the following spring, 

 produce mothers which bring forth their young alive. The individuals composing the late 

 brood having provided for the continuation of their race, generally die on the approach of 

 winter. 



