Abstract
Two major ecological factors determine the fitness of an insect herbivore: the ability to overcome plant resistance strategies (bottom-up effects) and the ability to avoid or resist attack by natural enemies such as predators and parasitoids (top-down effects). In response to differences in selection pressure, variation may exist in host-plant adaptation and immunity against parasitism among populations of an insect herbivore. We investigated the variation in larval performance of six different Plutella xylostella populations originating from four continents when feeding on a native Dutch plant species, Brassica rapa. One of the used populations has successfully switched its host plant, and is now adapted to pea. In addition, we determined the resistance to attack by the endoparasitoid Diadegma semiclausum originating from the Netherlands (where it is also native) and measured parasitoid performance as a proxy for host resistance against parasitism. Pupal mortality, immature development times, and adult biomass of P. xylostella differed significantly across populations when feeding on the same host plant species. In addition, parasitism success differed in terms of parasitoid adult emergence and their biomass, but not their development times. Variation among natural populations of insects should be considered more when studying interactions between plants and insects up the food chain.
Highlights
Insects are the most speciose group of organisms on earth
We examine the variation among populations of P. xylostella with respect to its performance, on a wild brassicaceous plant species (Brassica rapa L.)
The differences in the development times of the P. xylostella populations were more pronounced in males than in females, whereas the development times were quite similar for the parasitoid when developing on the different host populations
Summary
Insects are the most speciose group of organisms on earth. Their small size, the enormous variation in life-history traits, and physiological adaptations they exhibit allow them to adapt to living in virtually every terrestrial and freshwater habitat. Insect herbivores have to overcome a range of chemical and morphological defensive strategies that plants have evolved to prevent attack by herbivores and other attackers [3]. The short life-cycles of insects in variable environments could result in rapid genetic changes over generations giving rise to high levels of genetic heterogeneity, allowing them to respond rapidly to environmental change [4,5]. Phenotypic plasticity provides additional means to adapt to environments that change within the life cycle of an insect [6,7]
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