Relevance of visual and olfactory cues for host location in the mustard leaf beetle Phaedon cochleariae

Abstract

The relevance of visual and olfactory cues for host‐plant location is investigated in males and females of the oligophagous mustard leaf beetle Phaedon cochleariae Fabricius (Coleoptera: Chrysomelidae). Different objects are offered in a walking arena and the behaviour of beetles is observed. Beetles orient toward vertically or horizontally striped black and white pattern independent of stripe orientation. The results suggest that contrast facilitates orientation in the field, whereas the pattern itself may be less important for host location in dense vegetation. The response to green and yellow objects is tested to investigate discrimination abilities between young (green) and mature (yellow) leaves. Beetles prefer green over yellow independent of material (cardboard or leaves of Nasturtium officinale R. Br., Brassicaceae). Preference behaviour tested in a dual‐choice contact assay coincides with visual preferences, where adults prefer young, more nutritious leaves for feeding and oviposition. Furthermore, females discriminate between visual cues of green leaves and green cardboard, whereas males do not, indicating that females are more sensitive in colour discrimination. Differences in colour wavelength influence the choice of beetle behaviour more strongly than differences in intensity. Both sexes of P. cochleariae prefer volatiles of the host plant N. officinale, whereas only females respond to the main volatile compound 2‐phenylethyl isothiocyanate. Given a choice between visual and olfactory cues, males orientate towards the colour cues, whereas females do not show any preferences. In males, visual cues may thus override olfactory cues, whereas, in females, both are equally important, which may reflect different ecological requirements and/or physiological abilities.

Colour choice behaviour in the pollen beetle Meligethes aeneus (Coleoptera: Nitidulidae)

“…Also, the current trap data do not support the hypothesis that there are differences between male and female pollen beetles regarding their behavioural responses to spectral stimuli. This is in contrast to other studies that find sexual dimorphism with regard to colour choice behaviour in other beetle species (Crook et al , 2009; Kühnle & Müller, 2011).…”

Uncovering different parameters influencing florivory in a specialist herbivore

“…The superior role of visual cues is in line with other studies which revealed that visual cues of plant parts perceived by adult herbivores can be more relevant and override olfactory cues in host finding and location (Stenberg & Ericson, 2007;Kühnle & Müller, 2011). The possibility cannot be excluded that the excised condition in which flowers and leaves were offered affected the choice.…”

Reduce pests, enhance production: benefits of intercropping at high densities for okra farmers in Cameroon

“…In HD okra monocultures, the additional green surfaces were okra plants and thus leaf beetle numbers decreased only slightly in these plots in comparison with other HD plots. The importance of visual contrasts on beetles has been shown by previous studies . By contrast to leaf beetles and whiteflies, aphid abundance increased in HD plots.…”

“…Polyphagous aphids and whiteflies often respond to the spectra of greenish‐yellow light reflected by vegetation, or to the contrast in the plant–soil landscape, as they have not developed host‐specific olfactory cues. The relevance of visual cues in host‐searching abilities has also been shown for oligophagous leaf beetles . Therefore, it is evident that in intercropping systems the identity of the additional crop species, and of the pest, can be crucial in determining the pest suppression success of the intercropped field design.…”