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Egg dispersion is more important than competition type for herbivores attacked by a parasitoid
Authors:Steven M Vamosi  Michelle D den Hollander  Midori Tuda
Institution:(1) Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada;(2) Department of Zoology, University of Toronto at Mississauga, 3359 Mississauga Road N, Mississauga, ON, L5L 1C6, Canada;(3) Institute of Biological Control, Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan;(4) Present address: Lab Animal Services, Hospital for Sick Children, 555 University Ave, Toronto, ON, M5G 1X8, Canada;
Abstract:Herbivore fitness can be altered by a combination of interacting organisms, such as its food plant, conspecifics, and predators/parasitoids. Here, we tested relative effects of plant species, herbivore intraspecific competition type, and spatial distribution of the herbivore among plant units on herbivore survival and whether parasitoids modified these effects. We used an endophagous bruchine seed predator Callosobruchus maculatus for the herbivore, and a braconid wasp Heterospilus prosopidis for the parasitoid. The survival rate of C. maculatus was measured for each of 16 combinations of two plants (bean species, Vigna unguiculata and V. radiata), two competition types of C. maculatus larvae (contest and scramble), two spatial distributions of hosts sparse (1 C. maculatus larva per seed over 20 seeds) and dense (2 C. maculatus larvae per seed over ten seeds)], and with/without a parasitoid pair. In the absence of the parasitoid, C. maculatus survival rate was lower with V. radiata and in the contest type. With the parasitoid, the proportion parasitized hosts was independent of total host density. Neither the proportion of parasitized hosts nor host survival rate was affected by plant species or host strain, but they were affected by host spatial distribution. When host distribution was dense, a higher proportion of hosts were parasitized, and C. maculatus survival rate was lower. Here we discuss parasitoid potential as a selective agent for the sparse within-pod distribution of its hosts in the field.
Keywords:Aggregation  Bruchinae  Phytophagous insect  Refuge  Resource  Tritrophic interaction
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