Naive Fopius arisanus females respond mainly to achromatic cues

Parasitoids rely on a variety of visual and olfactory cues to locate exploitable resources. Their perception of colors is based on achromatic and chromatic information, though very few studies clearly distinguish the influence of both. We present here the results of field-cage experiments about the color perception of Fopius arisanus (Hymenoptera: Braconidae: Opiinae), an egg-pupal parasitoid of various fruit fly species (Diptera: Tephritidae). The tested insects were naive, fed and mated females. In all experiments, the wasps preferred the colors with the lower total reflectance in a spectrum of wavelengths above 450–500 nm. We conclude that F. arisanus females are not sensitive to the UV–blue part of the spectrum. Inversely we could not provide evidence that they are able of any hue discrimination, though the absence of response might indicate a lack of preference of naive females. Visual stimuli are predominant for F. arisanus females in close range landing site selection and even overrode the olfactory stimuli. The lack of innate preferences for chromatic cues is consistent with previous observations made on the specificity and the olfactory response of F. arisanus and may be related to the low innate specialization of this parasitoid. Its preference for dark colors matches the behavior of some polyphagous Tephritidae. It may reflect an innate attraction towards contrasted objects, as fruits appear within the foliage.