The spectrum of invertebrate seed predators that contribute to the control of the rape volunteer seeds (Brassica napus L.)

Volunteers originating from crop harvest losses can cause many serious problems in agroecosystems due to the competition with crops, admixture in harvest product, hosting of pests and diseases etc. Oilseed rape (Brassica napus L.) represents one of the most important volunteers worldwide. After the crop harvest, large quantities of seeds survive on the soil surface, where they stay until germination or enter the soil seed bank. Seed predation by herbivores is an useful tool that may significantly reduce the seed input in the soil seed bank and in this way reduce the abundance of volunteers in the subsequent crop. In this study, we investigated which groups of invertebrate seed predators are involved in the depletion of rape seeds on the soil surface. Nine carabid beetles (Coleoptera: Carabidae) and one terrestrial isopod (Crustacea: Isopoda: Oniscoidea) which were most abundant in pitfall traps placed in the rape fields were observed under laboratory conditions. Laboratory essay in which 50 dry seeds of winter rape were offered to individual beetles or isopods revealed that Pseudoophonus rufipes, Pterostichus melanarius and Amara ovata consumed the highest numbers of seeds per mass unit. Harpalus affinis, Poecilus cupreus, A. aenea, A. familiaris, and A. littorea consumed fewer seeds per mass unit, and H. signaticornis and the isopod species Armadillidium vulgare ate the rape seeds only occasionally. Surprisingly, carnivorous carabids significantly contributed to seed predation.