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BENEFICIAL VERSUS INJURIOUS INSECTS. 
Beneficial versus Injurious Insects. 
By EWEN . MACKINNON, B.A., B.Sc. 
Insects, though small in size, are capable of causing considerable 
damage and of producing much loss, but the enormity of the losses 
is not generally recognised. Their depredations are so varied, and 
yet so extensive, that all sections of the commun‘ty directly experience 
their attacks at some time or other. Let figures speak. The United 
States of America estimates for the annual losses on animal and plant 
producis average over 10 per cent. of the total value, and for 1915 are 
given as approximately £236,000,000; and for 1917, £260.000,000. On 
a similar estimate, the losses in Australia must have been in the vicinity 
of £18,000,000 in 1917, when the production was £183,000,000. 
While the damage done by insects is admitted to be enormous, it 
must not be supposed that all insects are injurious. As a matter of - 
fact, there are more insects that are either beneficial or non-injnrions 
than there are injurious forms, and man owes much to the beneficial 
insects, especially those that render good service in keeping the injurious 
forms in check. 
Beneficial insects have been broadly classed into five groups, as 
follows :— ae 
(1) Insects that prey on or are parasitic upon injurious forms. 
Many examples are to be found in the ladybirds, ground 
beetles, hymenoptera, and diptera (Hies). They are said 
to be entomophagous insects. 
(2) Insects that pollinate flowers, e.g., bees, ants, wasps, moths. 
(3) Insects that feed on dead or decaying organic matter, hence 
called Scavengers. : 
(4) Insects that serve as food for fish, birds, and other animal 
life. 
(5) Insects that secrete or elaborate substances of commercial 
value to man, ¢@.g., the honeybee, lace insect, silkworm, 
cochineal insect, 3 
It is the first group that interests us at the present time, though — 
reference may be made to two things before dismissing the other 
groups. he Soar be : 
(1) In connexion with the Sheep Blowflly problem, it has been 
suggested that greater use might be made of scavenger beetles. As the 
blowfly, and certain other flies that carry disease, breed in animal dung, 
it is possible that carrion beetles may help largely in the prevention of 
fly development by the destruction of much of the carrion—and jinei- 
dentally destroy many fly eggs and larve—in which flies develop. 
(2) The Gernians have always been most expert in their application 
of science to industry. In their search for fats during the war, they 
were practically exploiting. the blowfly. Millions of blowflies were 
induced to breed in fish waste. After the larve had reached a certain 
stage of development, they were used as a source of oil. As much as 
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