The effects of background pattern and contrast on prey discrimination by the praying mantis Sphodromantis lineola...

Tethered, adult female Sphodromantis lineola (Burr.) were presented with two groups of two-dimensional stimuli (i.e., 2-D lures) against various backgrounds. Lure Group 1 comprised various black rectangles in three different size arrays: each size array included a 2, 6, or 12 mm square, respectively, several 'worm' lures of a constant width (l2, edge perpendicular to the direction of movement, 3-30 mm), but varying in length (l1, parallel to the direction of movement, 6-114 mm), and several 'antiworm' lures of a constant length but varying width. Group 1 lures were presented against patterned backgrounds of similar luminance: one natural pattern mimicking foliage and the other a random geometric pattern of rectangles. Group 2 lures comprised various configurations and combinations of black and white lures which were presented against white, black, and natural pattern backgrounds. The appetitive behaviors of approaching and striking at a lure were dependent measures indicating that a stimulus was categorized as prey. For Group 1 lures, overall response rates to lures of the same size were enhanced by the natural pattern background rather than the geometric pattern background. Against the natural pattern background, worm lures were stronger releasers of predatory behavior than antiworm lures of the same size. Lure configuration (especially for the smallest array) was masked by the geometric pattern background, although worm versus antiworm discrimination was apparent with the largest size array. For Group 2 lures, lure-to-background contrast, as well as configuration, effected prey recognition. For instance, lures with low lure-to-background contrast ratios were weaker releasers than those with high ratios, and lures that were darker (versus lighter) than the background were stronger releasers. In addition, particular stimulus properties interacted to effect lure strength. For instance, a weak or strong releaser became stronger or weaker, respectively, when a more or less, respectively, preferred releaser was super-imposed. The results also suggest that S. lineola attends preferentially to the leading edge of a moving stimulus. These findings are in agreement with predatory behavior of praying mantises in the wild.