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Page:Popular Science Monthly Volume 72.djvu/413

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INSECTS INJURIOUS TO AGRICULTURE

inally from Australia, where it had rendered inestimable service in destroying mealy-bugs (Dactylopius, Eriococcus, etc.), and which, introduced into the Hawaiian Islands, developed with a surprising rapidity, comparable to that of Icerya in California. This ladybird is there considered as one of the most important enemies of the scale insects of the coffee plantations, and particularly Pulvinaria psidii, one of the greatest enemies of this crop. Coccinella repanda is also naturalized and is to-day one of the most common ladybirds, and most efficacious among those which attack orange plant-lice and the plant-lice of Hibiscus and sugar cane.

In 1899, Koebele left for Australia and the Fiji Islands and made numerous sendings of ladybirds and different parasites to the Hawaiian Islands, notably to combat Ceroplastes rubens Mask.

At the end of 1902 the attention of planters was particularly directed to an injurious leaf-hopper on the sugar cane, Perkinsiella saccharicida Kirk. It was introduced from Australia in about 1897 and has since that time increased and spread and become a perfect plague for this important crop. The attempts made to introduce living parasites in California at the expense of similar leaf-hoppers having given unsatisfactory results, Koebele and Perkins left in the spring of 1904 for Australia, and during the course of that year sent to Hawaii a great number of insects parasitic or predaceous, and among them a considerable quantity of enemies of Perkinsiella.

Considering that the money appropriated by the government was insufficient, the Hawaiian Sugar Planters' Association did not hesitate to advance important sums in order to further the study of the question, and created itself a section of entomology in its experimental station, and has started a series of investigations exclusively upon the enemies of sugar cane and their parasites. Some remarkable monographs are now in course of publication.

The method of utilizing beneficial insects has been, during fifteen years, used with such activity that the list of useful insects which have been imported from one country to another, in order to combat the plagues of agriculture, is already very long.

We have already spoken of some of them in giving a resumé of Koebele and Compere. Omitting those which up to the present time have given only uncertain results, or which have not succeeded in naturalizing themselves, we will limit ourselves to a mention of some interesting species, either because they have fully justified the hopes founded upon their introduction, or because they appear likely to soon play an important role in the struggle against the enemies of agriculture.

Rhizobius in California.—Among the ladybirds must at once be mentioned Rhizobius ventralis Erichs. This little ladybird, of a spe-