Spatio-temporal associations between the distributions of insect pests and their parasitoids in winter oilseed rape crops

Abstract: From the group of potentially important parasitoids of the pollen beetles (Brassicogethes aeneus), Tersilochus heterocerus adults were the most abundant in oilseed rape crops during 2016 and 2017. The second most common parasitoid species found was Phradis morionellus. Tersilochus tripartitus, the main parasitoid of cabbage stem flea beetles (Psylliodes chrysocephala) was recorded only during spring 2017 – it coincided with markedly higher levels of damage induced by P. chrysocephala larvae at the time. For Ceutorhynchus obstrictus, all three important pteromalids (Stenomalina gracilis, Trichomalus perfectus, and Mesopolobus morys) were recorded in similar abundances. From the known parasitoids of Dasineura brassicae, only Omphale clypealis was recorded in 2017. Significant spatial associations (p < 0.025) between the distribution patterns of B. aeneus adults and T. heterocerus adults (both sexes assessed together in this case) were recorded on some dates. The parasitisation of pollen beetle larvae by T. heterocerus proved to be high in untreated crops: on average 56% and 87.5-100% larvae were parasitized in 2016 and 2017, respectively). This indicates that parasitoids should be effective biological control agents of B. aeneus populations.