02094naa a2200193 a 450000100080000000500110000800800410001910000170006024501080007726000090018552015410019465000130173565300120174865300160176065300220177665300230179865300220182177300570184314177591993-09-03       1969    bl ---       0--  u    #d1 aSMITH, J. G.  aSome effects of crop background on populations of aphids and their natural enemies on brussels sprouts.  c1969  aThe work described is part of a programme aimed at elucidating biological factors that might be important in controlling pests of brassicas, especially brussels sprouts, and might therefore contribute to integrated control. These experiments were to assess the effect of variation in the crop background, caused by the absence or presence of weeds. The `background' to the crop is considered as the immediate surroundings of the crop plants, within the crop itself. Two different backgrounds were obtained by either clean weeding, to give an area of bare soil between the sprouts, or allowing the naturally occurring weeds to grow in a controlled manner. These weeds were cut back regularly to about 6 in. in height, to form a low-growig `carpet' beneath the sprout plants and so minimize competition between the crop and the weeds. Counts of aphid and of all stages of natural enemies on both sets of sprout plants and on the most common weeds were made at regular intervals. These weeds were fat hen (Chenopodium album L.), spurrey (Spergula arvensis L.) Polygonum persicaria L. and white and yellow charlock (Raphanus raphanistrum L. and Sinapis arvensis L.). Relative numbers of aphids and natural enemies were also assessed from catches of alatae and adult predators in yellow water traps. The only important aphid on the sprout plants was the cabbage aphid, Brevicoryne brassicae L.; aphids on the weeds consisted mainly of the black bean aphid (Aphis fabae Scop.) on C. album. Special attention was given to these species and ...  aEcologia  aAfideos  aDiversidade  aInimigos naturais  aInsetos - controle  aPragas - controle  tAnnals of Applied Biologistsgv.63, p.326-330, 1969.