212
H . KLOMP
1, = mean number of eggs or larvae per shoot.
grn = mean number of shoots/m2, i.e. the number present in the
(a) Mean number of eggs or larvae per shoot. N , is estimated by taking
samples of twigs cut off the trees. When larval density is measured
each sample is composed of twigs cut from six trees. These trees are
selected at random by going criss-cross through the study area, sampling
the tree which is nearest whenever 50 steps have been taken. The successive trees are numbered 1-6 and are sampled in three sacks of cloth
in the order 1-4, 2-5 and 3-6 (Fig. 2). Hence, in each sack the twigs of
two trees are mixed. It takes half a day to collect a sample of this size.
When egg density is measured two sacks are normally used, and four
trees are sampled.
A ladder is carefully placed in the tree, and the sack which can be
hooked on with open mouth to the branches (Fig. 2) is placed in the
lower part of the crown. Then a large number of twigs are cut off with
great care and collected in the sack. The twigs are cut off at the older
leafless parts and from all levels in quantities proportional to the size of
the crown (Fig. 2).
If the sample is used to estimate egg density the parts of the twigs
bearing needles are cut in pieces of about 5 cm and these are thoroughly
searched and any eggs found are collected. If the sample is used to
estimate larval density the sacks are successively placed in a container
which is gradually filled with carbon dioxide to anaesthetize the larva
which can be shaken off the twigs onto a cloth spread over the ground.
The effectiveness of this treatment is checked by repeating the whole
procedure. The larvae collected are stored in ethyl alcohol.
In the twig mass of each sack the number of yearling shoots is
counted. Pine trees produce new shoots at the tops of nearly all twigs
once a year in June (Fig. 2). These shoots can be recognized when fully
grown by the more light-coloured needles and the absence or smaller
amount of algae. These characteristics can be used up to May of the
following year.
The number of shoots present in a sack is used as an index of the size
of the sample. If their number/m2 were known, it would be possible to
calculate the density of eggs and larvae, provided some conditions are
fulfilled (see p. 217).
It takes two persons one whole day to handle a sample composed of
three sacks plus the counting of the shoots. As an example, some 1964
results are given in Table I. These show the variability of sample size
(column 4) and of larval density (column 6 ) . The results obtained on
three successive days can be pooled to calculate a mean density.
column just mentioned.
H . KLOMP
1, = mean number of eggs or larvae per shoot.
grn = mean number of shoots/m2, i.e. the number present in the
(a) Mean number of eggs or larvae per shoot. N , is estimated by taking
samples of twigs cut off the trees. When larval density is measured
each sample is composed of twigs cut from six trees. These trees are
selected at random by going criss-cross through the study area, sampling
the tree which is nearest whenever 50 steps have been taken. The successive trees are numbered 1-6 and are sampled in three sacks of cloth
in the order 1-4, 2-5 and 3-6 (Fig. 2). Hence, in each sack the twigs of
two trees are mixed. It takes half a day to collect a sample of this size.
When egg density is measured two sacks are normally used, and four
trees are sampled.
A ladder is carefully placed in the tree, and the sack which can be
hooked on with open mouth to the branches (Fig. 2) is placed in the
lower part of the crown. Then a large number of twigs are cut off with
great care and collected in the sack. The twigs are cut off at the older
leafless parts and from all levels in quantities proportional to the size of
the crown (Fig. 2).
If the sample is used to estimate egg density the parts of the twigs
bearing needles are cut in pieces of about 5 cm and these are thoroughly
searched and any eggs found are collected. If the sample is used to
estimate larval density the sacks are successively placed in a container
which is gradually filled with carbon dioxide to anaesthetize the larva
which can be shaken off the twigs onto a cloth spread over the ground.
The effectiveness of this treatment is checked by repeating the whole
procedure. The larvae collected are stored in ethyl alcohol.
In the twig mass of each sack the number of yearling shoots is
counted. Pine trees produce new shoots at the tops of nearly all twigs
once a year in June (Fig. 2). These shoots can be recognized when fully
grown by the more light-coloured needles and the absence or smaller
amount of algae. These characteristics can be used up to May of the
following year.
The number of shoots present in a sack is used as an index of the size
of the sample. If their number/m2 were known, it would be possible to
calculate the density of eggs and larvae, provided some conditions are
fulfilled (see p. 217).
It takes two persons one whole day to handle a sample composed of
three sacks plus the counting of the shoots. As an example, some 1964
results are given in Table I. These show the variability of sample size
(column 4) and of larval density (column 6 ) . The results obtained on
three successive days can be pooled to calculate a mean density.
column just mentioned.