Pollen beetle offspring is more parasitized under moderate nitrogen fertilization of oilseed rape due to more attractive volatile signal

Abstract

Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of their host’s plants, the emission of which is potentially dependent on the availability of soil nitrogen (N). This paper aimed at finding the optimal N fertilization rate for oilseed rape (Brassica napus L.) to favor parasitism of pollen beetles (Brassicogethes aeneus Fab. syn. Meligethes aeneus Fab.) in a controlled environment. Pollen beetles preferred to oviposit into buds of plants growing under higher N fertilization, whereas their parasitoids favored moderate N fertilization. As a part of induced defense, the proportion of volatile products of glucosinolate pathway in the total oilseed rape VOC emission blend was increased. Our results suggest that the natural biological control of pollen beetle herbivory is best supported by moderate N fertilization rates.