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

## TL;DR

This study shows that green light attracts a parasitic wasp used to control whiteflies, but standard LED traps don't disrupt this natural pest control method.

## Contribution

The study identifies green light as most attractive to Encarsia formosa and shows modified LED traps can monitor both pests and beneficial insects.

## Key findings

- Encarsia formosa is most attracted to green light (≈521–524 nm) in controlled and greenhouse settings.
- Standard LED-enhanced yellow traps rarely catch the wasp, making them safe for biological control.
- Modified traps with white or green backgrounds increased captures of both wasps and whiteflies at lower light levels.

## Abstract

Greenhouse whitefly is a serious pest of tomatoes and other crops. Growers often use yellow sticky cards to track its numbers, and newer traps with built-in light sources have made detection more reliable. However, there is a concern that these brighter traps might also lure in the whitefly’s natural enemy, a tiny parasitic wasp called Encarsia formosa Gahan (Hymenoptera: Aphelinidae) which helps keep whiteflies under control. We tested how this wasp responds to different trap colors and to lighted traps in controlled rooms and greenhouses, with and without whitefly-infested leaves. The wasp was most attracted to green light but, importantly, it was rarely caught by the standard whitefly monitoring trap that combines a yellow card with green light. This means the commonly used lighted trap can be used alongside the wasp without disrupting biological control. We also built modified traps with white or green backgrounds that increased the captures of both the wasp and whiteflies at lower light levels, suggesting that they could monitor both beneficials and pests at the same time. These findings support more precise, pesticide-saving pest management, helping growers protect crops while reducing environmental impacts.

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.