Abstract
Spatial variation in host plant availability may lead to specialization in host use and local host adaptation in herbivorous insects, which may involve a cost in performance on other hosts. We studied two geographically separated populations of the seed beetle Megacerus eulophus (Coleoptera: Bruchidae) in central Chile: a population from the host Convolvulus chilensis (in Aucó) and a population from C. bonariensis (in Algarrobo). In Aucó C. chilensis is the only host plant, while in Algarrobo both C. bonariensis and C. chilensis are available. We tested local adaptation to these native host plants and its influence on the use of another, exotic host plant. We hypothesized that local adaptation would be verified, particularly for the one-host population (Aucó), and that the Aucó population would be less able to use an alternative, high-quality host. We found evidence of local adaptation in the population from C. chilensis. Thus, when reared on C. chilensis, adults from the C. chilensis population were larger and lived longer than individuals from the C. bonariensis population, while bruchids from the two populations had the same body size and longevity when reared on C. bonariensis. Overall, bruchids from the C. chilensis population showed greater performance traits than those from the C. bonariensis population. There were no differences between the bruchid populations in their ability to use the alternative, exotic host Calystegia sepium, as shown by body size and longevity patterns. Results suggest that differences in local adaptation might be explained by differential host availability in the study populations.
Highlights
Plants are heterogeneous environments for herbivorous insects [1]
We found evidence of local adaptation in the population from C. chilensis for both variables measured: body size and longevity (Table 1, Fig. 1)
When reared on C. chilensis, individuals from the C. chilensis population were larger than individuals from the C. bonariensis population, while bruchids from the two populations had very similar body size when reared on C. bonariensis (Fig. 1A)
Summary
Spatial and temporal variation in availability and quality of resources may result in differential use of host plants, which can lead to specialization in host use. Most phytophagous insects are rather specialized in terms of host range [2,3,4]. The degree of specialization often changes along the distribution range of herbivorous insects [5,6], partly because their geographic distribution differs from that of their host plants. This results in localities where there are only few hosts available [7,8]. Insect species considered generalists may behave as specialists at a population level [5]
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