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alfalfa elds on ve dates in May, June and August 1996, and dissected a total of 643 aphids for larval A. ervi. Data were analysed with x2 test, blocked by eld and date.
Susceptibility of colour morphs to C. septempunctata on plants. We measured the susceptibility of the two aphid colour morphs to predation by allowing a single adult C. septempunctata to forage on caged alfalfa plants with 15 adults of each morph for 4 h; the experiment was replicated 27 times. After removing the predator from each plant, the number of remaining aphids of each morph was recorded and subtracted from 15 to determine the number consumed. The data were analysed with a 2-tailed, paired t-test. Use of colour cues by C. septempunctata. We investigated the use of colour cues by C. septempunctata by allowing single adult beetles to forage for aphids of both colour morphs in red, green and white containers. To maximize our ability to detect differences in predation rates between morphs, we designed the experiment as a split-plot, with background as the whole plot and aphid colour morph as the split plots. Each arena had a single background colour and 5 similar-sized (third or fourth instar) aphids of each colour morph. Predators foraged for 30 min, and at the end of the experiment the number of remaining aphids of each colour morph was recorded and subtracted from 5 to determine the number consumed. All predators foraged actively and consumed at least one aphid. Each treatment was replicated 20 times. Data were analysed as a split-plot analysis of variance. Comparison of reproductive rate of the colour morphs. The reproductive rates of the aphid colour morphs were compared by pairing 10 of each morph on individual caged alfalfa plants and allowing them to reproduce for 14 days. At the end of the experiment, all aphids of each morph was recorded. The experiment was started with 14 plants, but 2 plants were severely wilted after two weeks so these were excluded from the analysis. Data were analysed with a 2-tailed paired t-test.
Received 24 February; accepted 6 May 1997.
1. Falconer, D. S. & McKay, R. Introduction to Quantitative Genetics 3rd edn (Longman, New York, 1996).2. Rousseau, J. J. Letters on...