BENEFICIAL VERSUS INJURIOUS INSECTS. 
Beneficial versus Injurious Insects. 
“By EWEN MACKINNON, B.A., B.Sc. 
(I) 
There are three good examples of American work on an extensive 
scale on the control of injurious insects by the use of beneficial ones. 
They are (1) Californian work with: the “ladybird Hippodamia con- 
vergens, (2) work in the New England. States on the Gipsy and 
Brown-tail. Moths, and (3) work in the south-east with the Cotton 
Boll Weevil. 
The first is an example of the third phase previously mentioned, .e., 
the use of a native species, increasing by artificial means the number of 
individuals already present. Each year the State Insectary of Cali- 
fornia distributes several tons of Hippodamia convergens Guer., a native 
ladybird, to growers of apples, pears, prunes, cantaloupes, vegetables, 
seeds, and garden crops, for the destruction of many species of aphids. 
Previous to the adoption of this method of control the melon aphid 
(Aphis gossypii Gloy.) had practically prevented the growing of canta- 
loupes in California, as whole fields were ruined in three or four days. 
No mechanical or other means had been found effective, and it was only 
possible to get rid of the aphids by destroying the infected vines. The 
best results are obtained by placing colonies of ladybirds in the fields 
or orchards at or just before the first appearance of the aphids, the 
object being to prevent their increase. .The female ladybird, if the 
natural food is scarce, is thus forced to.search for the aphids, and will 
distribute her eggs in proportion to the number of aphids present. If 
the colonies were not placed until after the aphids had become 
abundant, she would deposit practically all her eggs at the same place. 
Orchards and fields have thus been kept clear of the aphid, and so great 
has been the demand for ladybirds that the State Insectary has been 
forced to organize upon a considerable scale and collect the Hippodamia 
in ever increasing quantities. 
Such numbers are not propagated at the Insectary. The numbers 
concerned are enormous, and the food required would be impossible to 
provide. A consideration of some of the figures will show this. A 
single consignment or a colony generally consist of 30,000 insects for an 
area of 10 acres, and is delivered by express trains and coaches, all 
charges paid, and with a free return for empty crates. | Approximately 
1,500 adult ladybirds weigh an ounce. Now 1,000 colonies containing 
approximately 30,000,000 individuals have been prepared for delivery 
at a time, and in the season 1918-19 as many as 75,000,000 were sent 
out, chiefly to grain and cantaloupe growers. The thousand colonies 
weigh about 4 ton, and the 75,000,000 weigh about 13 tons. That this 
number of ladybirds could be obtained, conserved, and distributed at the 
most favorable times is due to the scientific study of the question over 
a period of five or six years. Under the influences of many stimuli (e.g., 
temperature, moisture, hunger, light, and odour, &¢.), Hippodamia 
hibernates in enormous numbers in sunny well drained spots usually in 
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