none Various aspects of the parasitism of caterpillars of Ascia monuste orseis by Cotesia ayerzai, were studied in laboratory choice tests. Individual female female were found to be extremely variable in ovipositional duration, as well as in the number of eggs oviposited. To stimulate parasitoid dispersal, or low host density, we isolated female female for 60 min following initial exposure and compared our tests female female which had not been isolated. No differences in (1) the number of eggs oviposited per host instar; (2) the conditional probability of host encounter; (3) host acceptance; and (4) the conditional probability of instar specific parasitism were found between these groups. Held female did, however, reject host after ovipositor insertions in a higher proportion.