Response of apple maggot flies (Rhagoletis pomonella) to two‐dimensional, sticky‐coated inanimate models of trees erected in clearings in orchards showed that color, size, form, and orientation of model all played a role in eliciting fly arrival.
Among 122 × 244 cm vertical rectangular models of different colors, yellow, red, and black were the most attractive, green slightly less attractive, gray (about the same intensity of reflection as yellow) still less attractive, and white, aluminium foil, blue, and clear flexiglas least attractive. Both per model and per unit area, red vertical rectangles 122 × 244 cm were more attractive than smaller ones. Per model, the same was true for different‐size yellow vertical rectangles, but not per unit area. Yellow vertical models 3.0 m2 whose form was compact (circular, square, slightly rectangular or triangular) were more attractive than ones whose form was narrow and elongated. Vertical models were much more attractive than horizontal ones. Contour of edge (smooth or zig‐zag) was unimportant, but a model incorporating an alternating yellow and clear “checker board” pattern, shifting parallactically, elicited more R. pomonella arrivals than a solid yellow model. The normal inter‐tree flight pattern of R. pomonella was low, within 2 m of the ground.
As final evidence that visual stimuli play a role in tree detection, many more R. pomonella were intercepted on clear flexiglas sheets around a real cherry tree than around empty space (tree odor was not a factor).
We propose the following hypothesis to explain our findings. For an apple maggot fly in flight, a tree becomes visually discernible by its hue (fly reaction to yellow‐green) and/or the darkness of its silhouette (fly reaction to red‐black), but the latter only if the tree is large enough. The nearer a normally low‐flying fly approaches a tree, the taller becomes the silhouette and hence the more distinguishable the tree from the background. We have no evidence that any of the important visual cues are specific to host trees of R. pomonella.
Zusammenfassung
OPTISCHE REIZE, DIE FLIEGEN VON RHAGOLETIS POMONELLA ZU BÄUMEN ANLOCKEN
Die Untersuchung befaßt sich mit der Bedeutung von optischen Reizen für das Auffinden von (Wirts‐) Bäumen durch die Apfelfliege, Rhagoletis pomonella. Die Grundmethode besteht im Vergleich des Zuflugs freilebender Fliegen zu verschieden großen, zweidimensionalen, vertikal orientierten künstlichen Baummodellen. Diese wurden auf gerodeten Flächen innerhalb oder am Rand von Kirschen‐ und Apfelplantagen aufgestellt, 8–53 m von den nächsten Bäumen entfernt. Sie wurden mit “Bird Tanglefoot” fängig gemacht.
Von großen, rechteckigen Modellen (122 × 244 cm) in verschiedenen Farben erwiesen sich einerseits gelbe und grüne, andrerseits dunkelrote und schwarze als anlockend. Viel schwächer oder nicht attraktiv waren Grau (19–50% von Gelb), Weiß (20–33%), farbloses Plexiglas (21–26%), Aluminiumfolie (20%) und Blau (16%), die beiden letzten vielleicht sogar repellent. Kleine rote Rechtecke (15 × 30 cm) lösten ...
