126
N. WALOFP
probing response and the stimuli and receptors involved. In this study
the adults of Acyrt?mipho?t were seen to change their feeding sites on
the plant as the seed pods enlarged and this coincided with the movement of the alkaloid S p h i n e between the various plant organs. As
petals dropped off and pods began to grow, many adult8 and fourth
instar aphids left the stems and leaves and moved onto the pods where
feeding and reproduction recommenced. The movement w m not a result
of overcrowding aa there waa adequate surface area on stems and leaves.
In past years Sparteine has been used as a diuretic and a quantitative
estimation of its content in parta of broom showed that early in the
season shoot tips contained the largest quantities, but at flowering the
concentration fell rapidly and did not increase until the eecond flush
of growth and production of young shoots. The changes in its content
in leaves was similar and there was a large increase in absolute Sparteine
content in the pods m these developed and elongated (White, 1943;
Tattersfied et ul., 1926; blinist. of Agric. FiBh Fd BUU. (1964).
Smith (1966b) isolated Sparteine as a colourlese oil by the method of
Henry (1949) and experimented with the olfactory and gustatory responses of Acyrthosiphon. When parts of stems, leaves, pods and petals
were painted with Sparteine extract and aphids were introduced after
most of the alkaloid had soaked into tissues, the greatest number of
nymphs was found near the treated sites. Although Acyrtho8iph did
respond to some olfactory stimulus from crushed broom shoots, Smith
(be. cit.) considers that on the whole Sparteine acts as a gustatory
rather than as an olfactory stimulus. The wand movements of aphide
on the plant is coincident and is probably determined by the distribution of the alkaloid. The S p h i n e may be acting in broom aa a “token”
stimulus to stabilise Acyrthloaiphon in most favourable positions, and
the movements to the pods on the outsides of broom bushes is advantageous to the take off in flight of the alatae. Smith notes that many
different groups of chemicals have been reported aa stimuli which aid
host selection, but that this is the first report of stimulus by an alkaloid.
3. Factw8 checking the growth of population8 of Acyrthosiphon
Smith (196th) considers that the two factors that checked the rise
in the population of this aphid and caused its sharp decline were the
dispersal of alatae and predation by birds. He also considers that after
the decline, numbers were kept at a low level by the complex of
invertebrate predators.
(a) Production of alatae. As can be seen from Figs 3 , 4 and 6 the population peak in 1967 was approximately twice that in the 2 preceding
years and also that it was several weeks earlier. The numbers of the
future alatae (i.e. nymphs with wing pads) were also twice as numemua
N. WALOFP
probing response and the stimuli and receptors involved. In this study
the adults of Acyrt?mipho?t were seen to change their feeding sites on
the plant as the seed pods enlarged and this coincided with the movement of the alkaloid S p h i n e between the various plant organs. As
petals dropped off and pods began to grow, many adult8 and fourth
instar aphids left the stems and leaves and moved onto the pods where
feeding and reproduction recommenced. The movement w m not a result
of overcrowding aa there waa adequate surface area on stems and leaves.
In past years Sparteine has been used as a diuretic and a quantitative
estimation of its content in parta of broom showed that early in the
season shoot tips contained the largest quantities, but at flowering the
concentration fell rapidly and did not increase until the eecond flush
of growth and production of young shoots. The changes in its content
in leaves was similar and there was a large increase in absolute Sparteine
content in the pods m these developed and elongated (White, 1943;
Tattersfied et ul., 1926; blinist. of Agric. FiBh Fd BUU. (1964).
Smith (1966b) isolated Sparteine as a colourlese oil by the method of
Henry (1949) and experimented with the olfactory and gustatory responses of Acyrthosiphon. When parts of stems, leaves, pods and petals
were painted with Sparteine extract and aphids were introduced after
most of the alkaloid had soaked into tissues, the greatest number of
nymphs was found near the treated sites. Although Acyrtho8iph did
respond to some olfactory stimulus from crushed broom shoots, Smith
(be. cit.) considers that on the whole Sparteine acts as a gustatory
rather than as an olfactory stimulus. The wand movements of aphide
on the plant is coincident and is probably determined by the distribution of the alkaloid. The S p h i n e may be acting in broom aa a “token”
stimulus to stabilise Acyrthloaiphon in most favourable positions, and
the movements to the pods on the outsides of broom bushes is advantageous to the take off in flight of the alatae. Smith notes that many
different groups of chemicals have been reported aa stimuli which aid
host selection, but that this is the first report of stimulus by an alkaloid.
3. Factw8 checking the growth of population8 of Acyrthosiphon
Smith (196th) considers that the two factors that checked the rise
in the population of this aphid and caused its sharp decline were the
dispersal of alatae and predation by birds. He also considers that after
the decline, numbers were kept at a low level by the complex of
invertebrate predators.
(a) Production of alatae. As can be seen from Figs 3 , 4 and 6 the population peak in 1967 was approximately twice that in the 2 preceding
years and also that it was several weeks earlier. The numbers of the
future alatae (i.e. nymphs with wing pads) were also twice as numemua