Host-Range Extension by Native Parasitoids to Weed Biocontrol Agents Introduced to South Africa

The impact of host-range extension of native parasitoids to biological control agents of weeds in South Africa was investigated. Postrelease information was obtained for all of the insects released against weeds. Native parasitoids were recorded from 40% of the agents that established on their target weeds. All host-range extensions by native parasitoids were from native herbivores and occurred within 3 years of release. Susceptibility of the agents to attack by native parasitoids was influenced by their level of concealment and taxon. Poorly concealed endophytic agents were most susceptible to attack, whereas exposed feeders were fairly free from attack. However, native parasitoids did not strongly influence the populations of weed biocontrol agents and it was concluded that no biological control agent should be rejected solely on its susceptibility to attack by native parasitoids.