Can Eretmocerus eremicus Assess Oviposition Sites with Varying Host Densities and Predation Risks, and Make Decisions Based on Scent Cues?

Parasitoids use different signals to locate their hosts, and these signals can modulate their behavioral decisions. Thus, patch selection and foraging in patches with different characteristics depend on their ability to gather and use such information efficiently. In this study, we evaluated whether the parasitoid <i>Eretmocerus eremicus</i> (Hymenoptera: Aphelinidae), a natural enemy of <i>Trialeurodes vaporariorum</i> (Hemiptera: Aleyrodidae) on tomato plants (<i>Solanum lycopersicum</i>), uses scent cues to select and forage in patches that differ in host density and predation risk. Using choice bioassays in a wind tunnel under a continuous airflow, we recorded selection patch and selection time, as well as foraging parameters, including residence time, oviposition events, and attacks. Our results show that <i>E. eremicus</i> discriminated between sites with and without hosts using scent cues, but discrimination between patches with different host numbers was not detected under our assay conditions. It also distinguished between patches with maximum risk and those without risk, but not between subtle differences in risk. These findings suggest that <i>E. eremicus</i>, responded mainly to contrasting olfactory cues rather than to subtle odor differences. From an applied standpoint, our results motivate deeper investigation into how host- and predator-associated olfactory cues could fine-tune parasitoid deployment in biological control.