218
H. KLOMP
small quantities have been neglected in the computations of l m r d
density.
It is evident after these comments that the density can indeed be
expressed in numbers/ma according to relation (1). As shown in Table I
the mean number of larvae per shoot in 1954 on 10 August and 9 September is 0.0251 and 0.0252, respectively. Where S m amounts to 468,
larval density appears to be 11-5 and 11.5, respectively.
The calculation of a confidence interval for the estimate of the number of eggs or larvae/m2 has been made by the Department of Mathematics of the Agricultural University, Wageningen. The ultimate result,
the 96% confidence interval, can be formulated as follows:
where 1 = the mean number of eggs or larvae/m2.
=Student’s stochastic, the size of which depends on the
number of degrees of freedom, and the latter again on the
number of samples taken.
t
1 , = the estimated mean number of specimens/ma.
s = the standard deviation of W m .
In August 1954 B m amounted to 11.6 (Table I), t = 2.31 with 8
degrees of freedom, and s = 1.74. Consequently, the 95% confidence
interval equals 7.5-15-5 larvae/m2. In other years s is about equal to
16% of m, also.
2. The Density of Eggs
After larvae have hatched, the empty and transparent choria remain
attached to the needles for a considerable period but rarely for more
than a year. Such choria will be covered by algae, and can readily be
distinguished from freshly deposited eggs of the current year. Thus, egg
density can be estimated after the last eggs have been laid.
The last eggs are deposited about a fortnight after the emergence of
the last moths, which was determined from counts of emerging moths
in the field (see p. 229). Sampling normally fell in the period 6-20 July,
with some variations as a result of the prevailing spring temperatures.
Searching samples for eggs is very time-consuming (cf. p. 212), and
therefore sample size or number had to be relatively small. In most
years two or three samples (from eight or twelve trees) were taken,
containing an amount of 8-10 000 shoots, being roughly equivalent to
20-26 m2 ground surface.
In Table I1 the full results of a year with high and a year with low
density are presented to give the reader an idea of the variability of
H. KLOMP
small quantities have been neglected in the computations of l m r d
density.
It is evident after these comments that the density can indeed be
expressed in numbers/ma according to relation (1). As shown in Table I
the mean number of larvae per shoot in 1954 on 10 August and 9 September is 0.0251 and 0.0252, respectively. Where S m amounts to 468,
larval density appears to be 11-5 and 11.5, respectively.
The calculation of a confidence interval for the estimate of the number of eggs or larvae/m2 has been made by the Department of Mathematics of the Agricultural University, Wageningen. The ultimate result,
the 96% confidence interval, can be formulated as follows:
where 1 = the mean number of eggs or larvae/m2.
=Student’s stochastic, the size of which depends on the
number of degrees of freedom, and the latter again on the
number of samples taken.
t
1 , = the estimated mean number of specimens/ma.
s = the standard deviation of W m .
In August 1954 B m amounted to 11.6 (Table I), t = 2.31 with 8
degrees of freedom, and s = 1.74. Consequently, the 95% confidence
interval equals 7.5-15-5 larvae/m2. In other years s is about equal to
16% of m, also.
2. The Density of Eggs
After larvae have hatched, the empty and transparent choria remain
attached to the needles for a considerable period but rarely for more
than a year. Such choria will be covered by algae, and can readily be
distinguished from freshly deposited eggs of the current year. Thus, egg
density can be estimated after the last eggs have been laid.
The last eggs are deposited about a fortnight after the emergence of
the last moths, which was determined from counts of emerging moths
in the field (see p. 229). Sampling normally fell in the period 6-20 July,
with some variations as a result of the prevailing spring temperatures.
Searching samples for eggs is very time-consuming (cf. p. 212), and
therefore sample size or number had to be relatively small. In most
years two or three samples (from eight or twelve trees) were taken,
containing an amount of 8-10 000 shoots, being roughly equivalent to
20-26 m2 ground surface.
In Table I1 the full results of a year with high and a year with low
density are presented to give the reader an idea of the variability of