Summary: The chive gnat, Bradysia odoriphaga , is a notorious pest of Allium species in China. Colour trapping is an established method for monitoring and controlling of Bradysia species. In order to clarify the effect of colour preference of B. odoriphaga for the egg-laying substrate, multiple-choice tests were employed to assess the spontaneous response of the chive gnat to different colour hues and brightness levels under different intensities of white illumination and two spectrally different illuminations. Given the choice among four colours differing in hue under different intensities of white illumination and two spectrally different illuminations, chive gnat adults visited preferably the black substrate, a lesser extent to brown and green substrates, and the least extent to orange substrate irrespective of illumination. Given the choice among four levels of brightness under the same illumination conditions as those in the previous experiment (different intensities of white illumination and two spectrally different illuminations), chive gnats preferred black substrate over dark grey, and these over light grey and white substrates. Meanwhile, both virgin and copulated adults significantly preferred black over other colour hues and brightness. Based on our results, we conclude that the chive gnat adults significantly prefer black substrates irrespective of colour hues and brightness. This behaviour does not alter due to ambient light condition changes. No difference observed between choices of female and male adults. Our results provide new insight for understanding the colour choice behaviour in chive gnat and pave a way to improve monitoring and control of chive gnats and management. Summary statement: Chive gnat ( Bradysia odoriphaga ) innately prefer to move to black substrate irrespective of colour hues and brightness. This behaviour maintained the ambient lights change.

The light spectrum is a critical visual feature influencing insect behavior. The crepuscular moth Grapholita molesta (Busck), a significant pest of stone and pome fruits worldwide, has been shown to discriminate variations in brightness/intensity under dim‐light conditions. However, the behavioral responses of G. molesta females to various light spectra remain unknown. In this study, we investigated the oviposition preference of G. molesta females by assessing eggs laid in light and dark conditions, as well as under two different types of light in two‐choice experiments. Light in the upper canopy of Prunus persica is richer in UV light than lower parts characterized by a green light spectrum. When given the choice between light and dark, G. molesta females preferred to lay eggs in the illuminated areas over the dark ones. Further experiments revealed that when presented with colored light versus white light of the same intensity, or between two lights of different spectra, G. molesta females could discriminate between these light types. They exhibited a strong preference for ultraviolet (UV) light, followed by blue and green light. Notably, this preference for UV light was dependent on intensity, with higher intensity light attracting more female. In cases where spectrum and intensity cues conflicted (e.g., UV light was paired with lights that had 10‐fold or 100‐fold lower intensity), G. molesta females still showed a preference for UV light for oviposition. These results indicate that the crepuscular G. molesta can differentiate between various light spectra, and the preference for UV light likely aids females in selecting suitable oviposition sites during dusk.

The compound eye of the family Psyllidae (Hemiptera: Sternorrhyncha) remains one of the least studied among hemipteran insects. Among the approximately 4000 psyllid species worldwide, the pear psyllid Cacopsylla chinensis (Yang et Li) is a major pest of pear trees in China. The ultrastructure of the compound eye of adult C. chinensis was investigated using a transmission electron microscope (n = 12 adult). The eyes are of the apposition type, lacking a clear zone. Each ommatidium features a laminated corneal lens (about 16.9 ± 1.7 μm in diameter and 7.6 ± 1.7 μm in thickness), a eucone crystalline cone, a centrally fused rhabdom formed by eight retinula cells (R1–R8), and both primary and secondary pigment cells. The 57.0 ± 3.6 μm long rhabdom exhibits a two-tiered structure: a distal region comprising R1-R7 and a proximal region composed of R1-R6 and R8, with R7 withdrawing. Throughout this structure, the rhabdomeres of R1-R6 contribute continuously along the entire length, while R7 and R8 are restricted to the distal and proximal regions, respectively. The microvilli of the rhabdom are arranged in two orthogonal directions. Based on the similarity between the compound eye of C. chinensis and those of other diurnal hemipterans, the evolution and function of eyes are briefly discussed.

The light environment in orchards is highly heterogeneous, characterized by dappled light caused by sunlight filtering through plant canopies, and poses a challenge for the color perception of insects. For the crepuscular moth Grapholita molesta, a global pest of fruit trees, females can visually discriminate between plants to locate young leaves with higher brightness or intensity for oviposition around dusk. However, whether dappled light affects this brightness discrimination performance remains unknown. In this study, we investigated the oviposition preference of G. molesta females between two brightness stimuli (light-green and dark-green), as well as among three different light intensities under uniform light, simulated dappled light, and complex dappled light conditions at three ecologically relevant illuminances (100, 1, and 0.01 lx). G. molesta females laid significantly more eggs on light-green than dark-green stimuli under all three light conditions at each illuminance. Similarly, females consistently preferred high-intensity over lower-intensity light areas across uniform, dappled, and complex dappled light conditions, with more than 66% oviposition frequency. Our findings show that the brightness and intensity discrimination ability of G. molesta is not affected by dappled light, which may enable moths to accurately locate suitable oviposition sites even when the orchard canopy creates a heterogeneous light distribution.