Risks of plant damage caused by natural enemies introduced for arthropod biological control.

Abstract

Although the capacity to feed on both prey and plants is relatively widespread among pest natural enemies, mostly in predators, crop damage has rarely been reported. Little is known about the mechanisms governing crop damage occurrence by predators that can also facultatively feed on plants. This chapter aims to provide guidance on how to assess the risks of crop damage by introduced invertebrate biological control agents. Risks of crop damage do not seem to be characteristic and constant for each species but variable, depending on external factors. Based on the experience gained with the management of native facultative predators in conservation biological control, we discuss the role of variables linked to the predator, the crop plant and the target habitat when assessing risks of crop damage by introduced natural enemies. Among the variables related to the predator, capacity to consume and to injure plants and to vector plant pathogens are associated most with high risk of crop damage. When this information is not reliably available in the literature, pre-release tests must be carried out. These should include observations on plant-feeding activity and its confirmation by using chemical or immunological markers and gut content analyses. Specific trials, designed to test whether damage is caused, should take into account the variables linked to the crop that may affect its susceptibility: crop species, cultivar, growth stage and tissue. Risks posed by plant-feeding predators should be analysed in relation to the potential benefits expected from such predators for biological control.