The greenhouse whitefly (Trialeurodes vaporariorum Westwood, Hemiptera: Aleyrodidae) is a significant pest of tomatoes and other vegetables in greenhouses and relies on visual orientation to migrate and locate its host plant. Yellow sticky traps are frequently used to monitor this pest, and the recent integration of light-emitting diodes (LED) has significantly improved the attractiveness of these traps. However, it is unclear if the new LED trap also attracts its natural enemy, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), which might otherwise disrupt biological control. This study investigated the visual response of E. formosa to the new LED trap and further developed new LED trap variants for simultaneous monitoring of E. formosa and T. vaporariorum in the greenhouse for efficient biocontrol decision making process. Release - recapture experiments were conducted in the climate chamber and greenhouse using starved E. formosa less than 24 h old and adult whiteflies. The basic spectral reactivity of E. formosa was investigated in the climate chamber in a multiple-choice arena using 6 different LED colours, all set at the same intensity level. In each 20 replicates, 40 E. formosa were released from a glass vial at a distance of 0.7 m to the traps. Colour preference was estimated after 24 h. The response of E. formosa to whiteflies monitoring LED trap was further examined in choice and no-choice tests with and without hosts. Finally, the response of E. formosa and whiteflies to a modified version of the whiteflies LED monitoring trap were also evaluated in choice and no-choice tests in the presence and absence of hosts. Experiments without host were conducted at different time periods in the morning (9:00-12:00), afternoon (12:30-15:30), and evening (16:00-19:00) to assess daily activity and colour preference. Experiments with hosts lasted for 48 h. All experiments were completely randomized and replicated at most 20 times. The results showed that E. formosa exhibited the highest spectral reactivity for the green LED trap (521 nm). E. formosa also preferred the standard yellow sticky trap over whiteflies LED monitoring trap in host presence and absence. Modified versions of the LED trap increased E. formosa and whiteflies percentage recapture and were preferred by E. formosa at intensities less than 22 μmol m−2 s−1. Conclusively, whiteflies LED monitoring trap does not disrupt E. formosa biocontrol activities. Therefore, it is considered compatible for simultaneous use with E. formosa for whiteflies monitoring. Additionally, the modified versions of the LED traps show potential for simultaneous monitoring of E. formosa and whiteflies in the greenhouse. However, further validation of these traps under growing conditions in practice is recommended.
