DYNAMICS OF FIELD POPULATION O F PINE LOOPER
211
easily recognizable because their segments are more pronounced (Fig. 1).
This stage will be called “nymph” (= pre-pupa) in this paper.
The nymphs normally enter the upper layer of the litter and make a
small chamber lined with silken threads in which they pupate. The pupae
enter diapause, which is broken by low winter temperatures, after which
they are reactivated by rising spring temperatures (Schoonhoven, 1963).
For more details on the bionomics the reader is referred to Escherich
(1931).
c. THE PINE LOOPER AS AN OBJECT FOR POPULATION STUDIES
The pine looper, also named the bordered white, was suggested as a
suitable object for this study by the late Prof. L. Tinbergen. His starting point was that a long-term study of the factors affecting reproduction and mortality requires a habitat as stabble as possible, and as
already suggested by Varley (1963), forests am very well suited in this
respect. Secondly, the non-patchy distribution of this insect enables the
assessment of density with reasonable statisticid accuracy. Finally, this
species is by far the most numerous of the bigger insects living on pine
trees, and hence can be collected in all stages in sufficiently large numbers for rearing purposes (Klomp, 1962, Fig. 16).
11. METHODS OF MEASURINQ DENSITY
Density has been assessed in the egg, larvd, nymphal, pupal, and
adult stages of the insect. The methods used are quite different for the
stages living on the trees (egg and larva) and 1;he others. Nevertheless,
we were able to express all density data in nnmbers/m2. For eggs and
larvae this has been done indirectly via the amount of shoots, for the
others directly by counting the numbers/m“ ground surface. These
methods will be described briefly for the various stages.
A. DENSITY O F EQQS AND LIARVAE
1. Methods
The assessment of the density of the tree-living stages involved a
much more complicated method than those used for nymphs, pupae,
and adults because density had to be expressed in numbers per unit of
ground surface t o enable a direct comparison of the density of different
stages of the insect. The method used is based on the following formulation.
where R m = mean number of eggs or larvae per m2, i.e. the number in
an imaginary column with a brtse of 1 m2 and an unlimited height.
R m =Rs x B m
(1)
211
easily recognizable because their segments are more pronounced (Fig. 1).
This stage will be called “nymph” (= pre-pupa) in this paper.
The nymphs normally enter the upper layer of the litter and make a
small chamber lined with silken threads in which they pupate. The pupae
enter diapause, which is broken by low winter temperatures, after which
they are reactivated by rising spring temperatures (Schoonhoven, 1963).
For more details on the bionomics the reader is referred to Escherich
(1931).
c. THE PINE LOOPER AS AN OBJECT FOR POPULATION STUDIES
The pine looper, also named the bordered white, was suggested as a
suitable object for this study by the late Prof. L. Tinbergen. His starting point was that a long-term study of the factors affecting reproduction and mortality requires a habitat as stabble as possible, and as
already suggested by Varley (1963), forests am very well suited in this
respect. Secondly, the non-patchy distribution of this insect enables the
assessment of density with reasonable statisticid accuracy. Finally, this
species is by far the most numerous of the bigger insects living on pine
trees, and hence can be collected in all stages in sufficiently large numbers for rearing purposes (Klomp, 1962, Fig. 16).
11. METHODS OF MEASURINQ DENSITY
Density has been assessed in the egg, larvd, nymphal, pupal, and
adult stages of the insect. The methods used are quite different for the
stages living on the trees (egg and larva) and 1;he others. Nevertheless,
we were able to express all density data in nnmbers/m2. For eggs and
larvae this has been done indirectly via the amount of shoots, for the
others directly by counting the numbers/m“ ground surface. These
methods will be described briefly for the various stages.
A. DENSITY O F EQQS AND LIARVAE
1. Methods
The assessment of the density of the tree-living stages involved a
much more complicated method than those used for nymphs, pupae,
and adults because density had to be expressed in numbers per unit of
ground surface t o enable a direct comparison of the density of different
stages of the insect. The method used is based on the following formulation.
where R m = mean number of eggs or larvae per m2, i.e. the number in
an imaginary column with a brtse of 1 m2 and an unlimited height.
R m =Rs x B m
(1)