96 INDIRECT INJURIES CAUSED BY INSECTS. 
country both these plants suffer most are the Aphides, commonly called 
leaf-lice, but which properly should be denominated plant-lice. As almost 
every animal has its peculiar ouse, so has almost every plant its peculiar 
~~. plant-louse ; and, next to locusts, these are the greatest enemies of the 
vegetable world, and, like them, are sometimes so numerous as to darken 
the air.1 The multiplication of these little creatures is infinite, and almost 
incredible. Providence has endued them with privileges promoting fecun- 
dity which no other insects possess: at one time of the year they are 
viviparous, at another oviparous; and, what is most remarkable and 
without parallel, the sexual intercourse of one original pair serves for all 
the generations which proceed from the female for a whole succeeding 
year. Reaumur has proved that in five generations one Aphis may be the 
progenitor of 5,904,900,000 descendants; and it is supposed that in one 
year there may be twenty generations.? This astonishing fecundity ex- 
ceeds that of any known animal; and we cannot wonder that @ creature 
so prolific should be proporticnably injurious : some species, however, seem 
more so than others. Those that attack wheat, oats, and barley, of which 
there are more’ kinds than one, seldom multiply so fast as to’ be very 
noxious to those plants ; while those which attack pulse spread so rapidly, 
and take such entire possession, that the crop is greatly injured, and some- 
times destroyed by them. ‘This was the case with respect to peas in the 
year 1810, when the produce was not much more than the seed sown; 
and many farmers turned their swine into their pea-fields, not thinking 
them worth harvesting. The damage in this instance was caused solely 
by the Aphis, and’ was universal throughout the kingdom, so that a suffi- 
cient supply for the navy could not be obtained. The earlier peas are 
sown the better chance they stand of escaping, at least in part, the effects 
of this vegetable Phthiriasis. Beans are also often great sufferers from 
another species of plant-louse, in some districts, from its black colour, 
called the Collier, in others the Dolphin, which begins at the top of the 
plant, and so keeps multiplying downwards. The best remedy in this case, 
which also tends to set the beans well, and improves both their quality 
and quantity, is to top them as soon as the Aphides begin to appear, and 
carrying away the tops to burn or bury them, In a late stage of growth 
~_-great havoe is often made in peas by the grub of a small beetle (sruchus 
granarius), which will sometimes lay an egg in every pea of a pod, and thus 
destroy it. Something similar, I have been told (I suspect it is a short- 
snouted weevil), occasionally injures beans. In this country, however, 
the mischief caused by the Bruchus is seldom very serious; but in North 
America another species (B. pisi), which is also found here, but not to 
any very injurious extent, is most alarmingly destructive, its ravages 
having been at one time so universal as to put an end in some places to 
the cultivation of that favourite pulse. No wonder, then, that Kalm should 
have been thrown into such a trepidation upon discovering some of these 
pestilent insects just disclosed in a parcel of peas he had brought from 
that country, lest he should be the instrument of introducing so fatal an 
evil into his beloved Sweden.2 In the year 1780 an alarm was spread in 
1 Tsay this upon the authority of Mr. Wolnough of Hollesley (late of Boyton) in 
Suffolk, an intelligent agriculturist, and a most acute and accurate observer of 
nature, 
2 Reaum. vi. 566, 5 Kalm’s Travels, i, 178. 
