Oviposition‐induced plant cues: do they arrestTrichogrammawasps during host location?

Publisher Website
Google Scholar
Abstract
Plants can defend themselves against herbivorous insects before the larvae hatch from eggs and start feeding. One of these preventive defence strategies is to produce plant volatiles, in response to egg deposition, which attract egg parasitoids that subsequently kill the herbivore eggs. Here, we studied whether egg deposition byPieris brassicaeL. (Lepidoptera: Pieridae) induces Brussels sprouts plants to produce cues that attract or arrestTrichogramma brassicaeBezdeko (Hymenoptera: Trichogrammatidae). Olfactometer bioassays revealed that odours from plants with eggs did not attract or arrest parasitoids. However, contact bioassays showed thatT. brassicaefemales were arrested on egg‐free leaf squares excised from leaves with 72 h‐old egg masses, which are highly suitable for parasitisation. We tested the hypothesis that this arresting activity is due to scales and chemicals deposited by the butterflies during oviposition and which are thus present on the leaf surface in the vicinity of the eggs. Indeed, leaf squares excised from egg‐free leaves, but contaminated with butterfly deposits, arrested the wasps when the squares were tested 1 day after contamination. However, squares from egg‐free leaves with 72 h‐old butterfly deposits had no arresting activity. Thus, we exclude that the arresting activity of the leaf area near 72 h‐old egg masses was elicited by cues from scales and other butterfly deposits. We suggest that egg deposition ofP. brassicaeinduces a change in the leaf surface chemicals in leaves with egg masses. A systemic induction extending to an egg‐free leaf neighbouring an egg‐carrying leaf could not be detected. Our data suggest that a local, oviposition‐induced change of leaf surface chemicals arrestsT. brassicaein the vicinity of host eggs.