Visual and chemical cues in the host plant selection of the melon ladybird Chnootriba elaterii (Coleoptera: Coccinellidae)

Phytophagous insects employ various sensory cues in the host plant location such as visual, olfactory, gustatory, and tactile stimuli, which are perceived by sensory systems and integrated in higher brain centres to trigger the correct behavioural responses. In the present study, the host location process of the oligophagous species Chnootriba elaterii (melon ladybird) is investigated in controlled conditions using both a Y-Tube olfactometer and an open Y-Track olfactometer. Olfactory and visual cues from the host plant act synergistically to lead the ladybirds towards the host plant. Females of C. elaterii are not able to discriminate between host and non-host plants using either olfactory or visual cues alone. Visual cues, particularly those associated with the colour green, are of higher relative importance compared to olfactory cues in the host location process. Green dummy plants made of cardboard represent strong supernormal stimuli for C. elaterii females. The results of the present study can shed light on the host location process of Coccinellidae and can help to develop visual or chemical traps which can be useful in monitoring and controlling this important crop pest of the Mediterranean Basin.