ABSTRACT
In the annual speech given by the President of the Washington Entomological Society, C. V. Riley chose to deal with an area that had no particular relationship with the events of the year in course or the life of the Society. A simple look at the living world shows the importance of the many diverse forms of parasitism in both animals and plants. The phenomenon of parasitism holds great interest from the perspectives of morphology, biology and evolution. The subject is so vast that only the parasitism of insects will be discussed. Among the vertebrates, some are affected, such as the primates, the carnivores, domestic herbivores and birds; elephants and bats are affected by specific parasites. Others are affected to a lesser extent, such as the insectivores and reptiles, or escape altogether, such as the marsupials and Edentatae. The other classes are relatively free of parasites. As for the arthropods, most orders of insects are preyed on by organisms from their own class. The etymology of the term “parasite” (“he who eats at the table of another”) is accurate enough, but applies more particularly to true parasites, which live off the host without necessarily harming it. A classification of parasites is proposed: true parasites (which would not exist without their host), fatal parasites (entomophages) and parasites which live off other insects. The study of parasitism in the Hexapoda will be done by order, beginning with the hymenoptera. (...)
[The part not presented deals successively with the following orders: Coleoptera, Diptera, Hemiptera, Lepidoptera, Platyptera, and Arachnida; the evolutionary origins of parasitism in insects and its harmful effects are then discussed.]
The economic impact of parasitism is then examined, in particular from the point of view of farmers and livestock breeders. It is clear that the harm caused to domestic animals by external parasites is insignificant compared to the economic benefits of parasites on herbivorous insects. Many swarms of harmful insects are stopped by the sudden multiplication of certain hymenoptera. The victory of Riley over the Australian cochineal Icerya purchasi by the introduction in California of its predator the ladybird Vedalia (Novius) cardinalis attracted attention to the economic importance of this type of method for fighting against crop enemies. In conclusion, the speaker points out that he has not been exhaustive; in particular, he did not deal with the question of insects that provoke galls on plant tissues, nor that of the modifications of cocoons by parasitism, nor the psychic impact of parasitism on the insect prey. Finally, the fact that parasitism is most marked in the most evolved forms might indicate that this phenomenon appeared late in the evolutionary history of insects on the planet.
