Almost no information is available on the host specificity of introduced insect natural enemies. Over the years, records have been kept on the numbers, identity, and hosts of biological control agents that have been introduced into South Africa. Here we illustrate that only seven of the 45 species of chalcidoid agents introduced into South Africa are recorded as monophagous, the rest being oligophagous or polyphagous. In Africa, at most, 33% of the 145 described indigenous species of Aphelinidae and 49% of the 372 described species of Encyrtidae for which host information is available, are tentatively considered as monophagous. This lack of host specificity among most of these chalcidoids provides ample evidence that there should he a phasing-in of prescreening trials, using a small selection of possible nontarget species for each agent.