Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: May 2, 2010
Publication Date: September 1, 2010
Citation: Sforza, R. 2010. Collecting and evaluating biocontrol candidates (in French). Book Chapter. Recherche et évaluation des candidats pour la lutte biologique classique. In “La lutte biologique. Vers de nouveaux équilibres écologiques". pp280-85. Lydie Suty (Eds). Collection Sciences en partage. Coéditions Quae-educagri. 324p.
An important criterion for selecting potential classical biocontrol agents for weeds and insect pests is that agents will be reasonably host-specific and not become pests themselves. It is commonly accepted that each invasive species is attacked by a minimum of 15 natural enemies in its native range, but all will not be appropriate as biocontrol agents because of lack of specificty. In order to evaluate the level of host specificity between a natural enemy and its target plant or insect, a variety of tests are undertaken for selecting the best candidates to be released in the area invaded by the pest species. In the case of weed biocontrol, evaluating the host-specifity of a seed feeding insect on a target species requires testing it against a list of close relatives of the target species. For that purpose, a list of 20 to 50 plant species is selected according to a centrifugal approach; starting with species and sub-species in the same genus, then related genera and related families as well as crops with high economic impact, endangered species, and native and protected species in the introduced range. Seeds of each species are obtained from botanical gardens and other sources, then grown and placed together with the natural enemy in controlled experiments. Feeding activity and oviposition tests are performed to assess the potential host range of a herbivore. No-choice tests (i.e. testing a single plant species) are conducted, providing an easy way to ascertain which plant species are definitely not suitable hosts and quickly eliminating them from further consideration. In comparison, biocontrol tests for natural enemies of insect pests are faster and easier. Parasitoid insects used against important crop pests such as scale insects, aphids, and moths, often present a high degree of specificity for their host. In addition, unlike phytophagous natural enemies, parasitoids cannot become pests.