Phototactic Response of <i>Conotrachelus psidii</i> Marshall, 1922 (Coleoptera: Curculionidae) to Light Spectra: Implications for Light Trap Development in Guava Orchards

ABSTRACT Throughout their evolution, insect species have adapted in different ways to light stimuli, exhibiting phototactic behaviours that vary according to the wavelength, intensity and quality of light. In this study, the phototactic response of Conotrachelus psidii Marshall, 1922 (Coleoptera: Curculionidae) to different light spectra was evaluated. To perform the bioassays, adults of C. psidii were collected from guava orchards and placed in a phototactic arena consisting of three sections: two lateral sections containing light sources and a central section designated for insect release. Six LED light sources were used: red (612 nm), yellow (594 nm), green (520 nm), blue (455 nm), white (449 and 535 nm) and ultraviolet (365 and 405 nm). A total of 360 adults were evaluated in three experimental assays: (1) unsexed insects exposed to one light at a time; (2) sex‐separated insects exposed to one light at a time; and (3) unsexed insects exposed to two lights simultaneously. The effect of light exposure on the duration of thanatosis behaviour was also evaluated, justified as an antipredator strategy that may influence the dispersal and survival of C. psidii adults under field conditions. The results indicated that red light elicited a significantly higher positive phototactic response (approximately 65% of males moved toward the red light) in males, whereas females did not show significant attraction to any spectrum. Both sexes showed significant aversion to ultraviolet (UV) and white light, with less than 20% of adults entering these sections. In the choice tests, red light attracted significantly more adults than yellow, green and ultraviolet lights. Exposure to different light spectra also affected the duration of thanatosis, with males exhibiting longer immobility under blue light and females under dark and blue‐green conditions, suggesting sex‐specific behavioural strategies. The results suggest that red light can be cautiously considered for developing selective light traps for monitoring C. psidii in Integrated Pest Management (IPM) programmes, contributing to early detection and improved pest management in guava orchards.