Abstract
The preference–performance hypothesis (PPH) states that herbivorous female insects prefer to oviposit on those host plants that are best for their offspring. Yet, past attempts to show the adaptiveness of host selection decisions by herbivores often failed. Here, we tested the PPH by including often neglected oviposition-induced plant responses, and how they may affect both egg survival and larval weight. We used seven Brassicaceae species of which most are common hosts of two cabbage white butterfly species, the solitary Pieris rapae and gregarious P. brassicae. Brassicaceous species can respond to Pieris eggs with leaf necrosis, which can lower egg survival. Moreover, plant-mediated responses to eggs can affect larval performance. We show a positive correlation between P. brassicae preference and performance only when including the egg phase: 7-day-old caterpillars gained higher weight on those plant species which had received most eggs. Pieris eggs frequently induced necrosis in the tested plant species. Survival of clustered P. brassicae eggs was unaffected by the necrosis in most tested species and no relationship between P. brassicae egg survival and oviposition preference was found. Pieris rapae preferred to oviposit on plant species most frequently expressing necrosis although egg survival was lower on those plants. In contrast to the lower egg survival on plants expressing necrosis, larval biomass on these plants was higher than on plants without a necrosis. We conclude that egg survival is not a crucial factor for oviposition choices but rather egg-mediated responses affecting larval performance explained the preference–performance relationship of the two butterfly species.
Highlights
Host-plant selection for oviposition by insect females is a decisive step in establishing a new herbivore generation (Thompson 1988a, b; Thompson and Pellmyr 1991; Gripenberg et al 2010)
We addressed the following questions: (1) is oviposition choice of two pierid species, P. brassicae and P. rapae affected by the plant species’ capability to activate an egg-killing response (i.e., hypersensitive response (HR)-like necrosis)? (2) Do females prefer to oviposit on plants on which their eggs show highest survival rates and larvae perform best? (3) Do plant-mediated effects of eggs change caterpillar performance and if so (4) do they correlate with butterfly oviposition choices?
Arabidopsis thaliana, which was in the flowering stage, did not receive any egg clutches from P. brassicae in this setup
Summary
Host-plant selection for oviposition by insect females is a decisive step in establishing a new herbivore generation (Thompson 1988a, b; Thompson and Pellmyr 1991; Gripenberg et al 2010). The vast majority of innumerable laboratory studies testing the PPH did not consider that plants can activate defenses in response to egg deposition. The effects of egg deposition on subsequent plant defenses against larvae have been mainly overlooked until recently, with most studies on larval performance conducted by placing larvae onto an egg-free host plant (Hilker and Fatouros 2015, 2016)
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