Vision Fixation of Flightless Monophagous Leaf Beetle Ambrostoma quadriimpressum in Relation to Host Location

Abstract

The leaf beetle Ambrostoma quadriimpressum (Coleoptera: Chrysomelidae) is monophagous on elm trees, Ulmus pumila (Ulmaceae). As this species lives on elm during most of its life but pupates and overwinters as an adult in the soil, the flightless beetle seeks a host plant after emergence from the soil. Previous field experiments showed that the beetle locates host plants via orientation to standing black targets and does not recognize host plant prior to contact it. In order to establish the relationship between preferential vision fixation and host locating behavior, we investigated the visual orientation by placing individuals in the center of an arena and recording their responses to different targets at the perimeter. Responses were compared for a control object - a vertically positioned 10 × 30 cm black rectangle - versus a treatment object that differed from the control in terms of width, height, orientation, edge features, or color. Higher, wider, vertical, and solid black objects were more attractive to the beetle than objects that are shorter, thinner, inclined or have stripes, whereas two altering features (wavy or serrated) of the target’s vertical edge had no effect. The red and black targets were equally attractive, whereas blue, green or yellow objects were less attractive than black ones, and adding a green disk at the top of a black target did no enhance attraction. These visual preferences corroborate that the beetle is attracted to objects that resemble a tree trunk during the field search for a host. The implicated mechanism of vision fixation and host locating pattern of this beetle are discussed.