responses of the pollen beetle, Meligethes aeneus, and the seed weevil, Ceuthorhynchus assimilis, to oil-seed rape, Brassica napus, and other plants

(1) Adult pollen beetles often occurred abundantly on early flowering cruciferous and non-cruciferous plants growing on verges of rape crops, but when the crop flowered they became more numerous on rape plants at the crop edge. When the crop ceased to flower, new generation pollen beetles moved on to flowering verge plants. (2) Adult seed weevils were restricted almost entirely to cruciferous species; the presence of exudate of non-cruciferous plants could deter feeding. They infested verge plants sooner than crop plants. There was no innate preference for plant species, but seed weevils soon became conditioned to the plants on which they were feeding and subsequently preferred them. Seed weevils oviposited less readily than pollen beetles in wild cruciferous plants. (3) Pollen beetles and seed weevils were attracted to traps baited with extracts of cruciferous plants or the mustard oil, allyl isothiocyanate. Opened flowers and yellow buds were favoured more than green buds, and individual pollen beetles and seed weevils responded to the sight of others on a raceme, resulting in aggregations.