Spectral Preferences of Encarsia formosa: Unravelling Attraction to LED Monitoring Traps

LED-enhanced sticky traps improve monitoring of greenhouse whitefly, Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), but their effects on its parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), are unclear, which may compromise biological control. Methods: We quantified E. formosa visual responses in climate-chamber multiple-choice arenas using six LED colors at equal photon flux (8.1 μmol m ⁻² s ⁻¹) and in greenhouse choice/no-choice assays comparing a standard yellow sticky trap with a green LED-enhanced yellow trap, with and without host-infested tomato leaves. We further tested modified LED traps (green LEDs with white or green backgrounds) and assessed intensity-dependent responses (18.0–25.6 μmol m ⁻² s ⁻¹). Results: E. formosa showed the highest attraction to green LEDs (peak ≈ 521–524 nm) and a significantly lower response to other colors. In greenhouse assays, E. formosa preferred the standard yellow sticky trap over the LED-enhanced yellow trap; in no-choice tests, only 9% were recaptured on the LED-enhanced yellow trap, both without and with hosts. Modified traps with white or green backgrounds substantially increased E. formosa recapture (≈54% higher than the yellow-background LED trap). Encarsia formosa attraction to the white-background LED trap declined with increasing intensity (61% at 18.0 to 4% at 25.6 μmol m ⁻² s ⁻¹), whereas whitefly captures were stable to slightly higher. Conclusions: The standard LED-enhanced yellow trap is compatible with E. formosa releases and does not disrupt biocontrol. Modified LED traps show promise for simultaneous monitoring of E. formosa and whiteflies, warranting validation under commercial conditions.