Comparative function of blacklight and visual light sources in capturing Harmonia axyridis in the field and laboratory conditions; effect of color polymorphism

Abstract

Abstract Light trapping is one of the most popular sampling methods for monitoring pests’ populations in IPM programs. Harmonia axyridis (Coleoptera: Coccinellidae), which is a voracious aphid predator, needs to be monitored for several reasons; e.g. for its function as an invasive alien species newly appeared in many non-native countries. Lots of studies and observations show that this ladybird is significantly attracted to blacklight traps. Two major color morphs of H. axyridis (melanic and nonmelanic) appear with different ratios in different populations. In this study, the outcome of two sampling methods, including light trapping and foliage beating were evaluated in terms of the color morph combination and sex ratio in the field. Also, two types of light sources (blacklight (UV) and visual light LED) were compared in attracting the two color morphs in the laboratory conditions. Field results, where the ladybirds could fly towards the light source, indicated that blacklight trap captures less melanic individuals compare to mercury light trap and foliage beating, while there was no difference between the two latter methods. Also sex ratios were not different among the sampling methods. However, blacklight (UV) and visual light sources did not show any effect on attracting the two morphs in laboratory conditions, where the ladybirds could only walk towards the light sources. Comparing the results from field and laboratory experiments suggest that H. axyridis shows different phototaxic reactions based on its locomotion options.