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Insects can be excluded from control plants by caging them before the agent establishes on those plants, or by spraying them with a non-residual insecticide after they have been caged. The reverse approach may also be made of adding insects to some cages but not to control cages. Cages are usually made with a metal or timber frame covered by gauze with apertures small enough to prevent entry by the agent. Particular attention must be paid to sealing joins in the gauze, the junction between the cage base and the soil, and the entry point allowing access for sampling.
The advantages of exclusion by cages are that:
 | controls and treatments can be at the same site; |
| it can be used when the biological control agent is already widespread. |
The disadvantages of exclusion by cages are that:
| cages are susceptible to damage by wind, livestock and vandals; |
| cages can significantly modify plant growth; |
| insect behaviour and population growth can be significantly altered by confinement in the cage, and protection from predators, parasitoids
and weather; |
| experiments are restricted to the spatial scale of the cages. |
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Grant Farrell and
Mark Lonsdale
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