STUDIES ON THE I N S E d FAUNA ON SCOTCH BBOOM
117
Two methods were used for estimating the total number of eggs laid
throughout the s e w n :
(a) Small corm of soil (2.46 cm diameter and 18 cm deep) were taken
at regular intervale and the eggs and larvae were extracted by a
modification of the Salt and Hollick (1944) method. In the modification (Danthanarayana, 1906) the material collected after floatation
was washed free of magnesium sulphate and centrifuged with a
saturated solution of sodium chloride. The living and hatched eggs
of Sitona and the larvae floated to the top, while the vegetable
matter was deposited at the bottom. The eggs remained alive and
both Sitona larvae and their parasites hatched from them.
(b) Samples of field females were caged at regular intervals and the
numbers of eggs laid by them were counted. The weekly number
per female was multiplied by the female population on broom.
Methods (a) and (b) agreed fairly closely and gave the following
estimatea:
691 eggs/female (a)
642 eggs/female (b)
262 eggsffemale (a)
296 eggs/female (b)
1903 (
1964 (
I n estimating the recruitment of individuals and mortality within
each stage Danthanarayana considered that the method proposed by
Richards and Waloff (1964) best fitted the 8itona data. This method is
based on the calculation of the slope in the population after the peak
number has been reached and on the assumption that the time trend
of the population will fit the formula Y = nK*, where ( Y ) is the population on day (t), (n) is the number of eggs bid or larvae hatched or
moulted and (K) is the fraction surviving each day. The logarithms of
(Y) for the values after the peak will follow a straight line, since
log Y = log n + t log K. The numbers entering a stage will be given by
the value Y found by inserting into the equation a value of (t) corresponding to the start of the stage.
Life tbtbltw based on the above estimates were constructed and are
presented in Table XIV. This table shows that the greatest mortality
occurred in the egg and in the early first instar stages, before the larvae
could find or arrive at the feeding sites. The total mortdity of these
two stages in 1963 and 1964 amounted to 96.0 and 92.9%. As the
fecundities in the 2 years were 691 and 262 per femde and the sex ratio
was approximately 1 : 1, Table XV was constructed. The percentages of
total mortality in both years were slightly lower than those necessary
for stability (i.e. the differences were equal to +0-14y0 and + 0 . 0 9 ~ o )
and these are reflected in the slight rises in the population.
117
Two methods were used for estimating the total number of eggs laid
throughout the s e w n :
(a) Small corm of soil (2.46 cm diameter and 18 cm deep) were taken
at regular intervale and the eggs and larvae were extracted by a
modification of the Salt and Hollick (1944) method. In the modification (Danthanarayana, 1906) the material collected after floatation
was washed free of magnesium sulphate and centrifuged with a
saturated solution of sodium chloride. The living and hatched eggs
of Sitona and the larvae floated to the top, while the vegetable
matter was deposited at the bottom. The eggs remained alive and
both Sitona larvae and their parasites hatched from them.
(b) Samples of field females were caged at regular intervals and the
numbers of eggs laid by them were counted. The weekly number
per female was multiplied by the female population on broom.
Methods (a) and (b) agreed fairly closely and gave the following
estimatea:
691 eggs/female (a)
642 eggs/female (b)
262 eggsffemale (a)
296 eggs/female (b)
1903 (
1964 (
I n estimating the recruitment of individuals and mortality within
each stage Danthanarayana considered that the method proposed by
Richards and Waloff (1964) best fitted the 8itona data. This method is
based on the calculation of the slope in the population after the peak
number has been reached and on the assumption that the time trend
of the population will fit the formula Y = nK*, where ( Y ) is the population on day (t), (n) is the number of eggs bid or larvae hatched or
moulted and (K) is the fraction surviving each day. The logarithms of
(Y) for the values after the peak will follow a straight line, since
log Y = log n + t log K. The numbers entering a stage will be given by
the value Y found by inserting into the equation a value of (t) corresponding to the start of the stage.
Life tbtbltw based on the above estimates were constructed and are
presented in Table XIV. This table shows that the greatest mortality
occurred in the egg and in the early first instar stages, before the larvae
could find or arrive at the feeding sites. The total mortdity of these
two stages in 1963 and 1964 amounted to 96.0 and 92.9%. As the
fecundities in the 2 years were 691 and 262 per femde and the sex ratio
was approximately 1 : 1, Table XV was constructed. The percentages of
total mortality in both years were slightly lower than those necessary
for stability (i.e. the differences were equal to +0-14y0 and + 0 . 0 9 ~ o )
and these are reflected in the slight rises in the population.