specifieity for S. invicta exhibited by the Formosa biotype is the result of a higher

proclivity to attack or attempt oviposition on S. invicta than on S. xyloni.

 Comparisons between the Formosa and Las Flores biotypes with S. gentinata,

demonstrate that hovering flies in the no-choice tests (Table 2-1) were more host specific

to S. invicta in the Las Flores biotype than the Formosa biotype (89% vs. 36%).

However, in regard to pupal production, the Formosa biotype was 100% host specific to

S. invicta while the Las Flores biotype was 94% host specific (Table 2-1); in other words,

a few of the Las Flores flies were able to develop on S. gentinata but none of the Formosa

flies were able to develop. In the paired preference tests, percent preference for S. invicta

over S. gentinata was higher in the Formosa biotype than the Las Flores biotype (87% vs.

78%; Table 2-1). Host specifieity as calculated by attack rates was also higher in the

Formosa biotype than the Las Flores biotype (94% vs. 86%; Table 2-1). Since the rate of

pupal production was zero in both the no-choice and paired preference tests for S.

gentinata (Figs. 2-1 and 2-2), I conclude that the Formosa biotype will not be a threat to

S. gentinata. These trials demonstrate that the Formosa and Las Flores biotypes differ

substantially in host specificity.

 Vink et al. (2003) also observed variability in host specificity between two biotypes

of2~icroctonZus acrlib~'iopside (Hymenoptera: Braconidae). Other studies on the host

specificity of parasitoid biotypes have shown that geographic variation in host specificity

between biotypes was due to the presence of cryptic species (Heimpel et al. 1997,

Alvarez and Hoy 2002). Although my results demonstrate that there is geographic

variation between the Formosa and Las Flores flies, I cannot rule out the possibility that

the variability seen is due to the presence of a cryptic species.