302
H . KLOMP
disadvantage of still greater effect? The answer to this question will
necessarily be hypothetical, and is presented here merely as a suggestion.
Herrebout et al. (1963) have shown that the larvae of the pine looper
are highly camouflaged in their natural environment of pine needles as
a result of their colour pattern and habits of resting and feeding. Moreover, they have given strong arguments in favour of the view that the
fact of being camouflaged has functional significance, because it protects the insects against the attacks of enemies hunting by sight.
Referring to evidence from the literature the authors point out that the
effectiveness of the camouflage is increased by a solitary way of life:
“the longer the interval between encounters of an individual enemy
with specimens of the camouflaged prey, the more the experience
gathered by the enemy in a previous encounter will have waned before
the next takes place”. The same conclusion is reached by Brower (1958).
Furthermore, by comparing the effectiveness of the camouflage of
different pine inhabiting species, it was shown by Herrebout et al. that
the species with the most cryptic colour pattern also showed the best
adapted habits, and it was concluded that the different components of
the camouflage tend to vary in the same direction and amount, as if
being linked together.
The pine looper appears to have reached the most perfect degree of
concealment in both colour pattern and habits, and consequently it may
also be expected to have developed a mechanism to keep the larvae
separate and dispersed. This supposition is suggested by the fact that
the larvae of gregarious and aposematic species (Diprion p h i , Neodiprion sertifer) have developed special behaviour patterns to keep the
insects together (Prop, 1960).
Having reached this point we will return to the mutual interference
among larvae described in this paper. As reported earlier, the female
moth deposits the eggs in batches ranging from 2 to 25, with an average
of 6. Pine trees have a thin structure, with the twigs fairly well separated, and the pine looper larvae are rather inactive creatures. Consequently, the individuals of one batch might easily remain together for a
considerable period, when they are not stimulated to disperse. This will
be disadvantageous because enemies (birds) might readily learn that
having found one larva, some more will be present in the immediate
neighbourhood, and the predator might well develop a “searching
image” for such prey species (Tinbergen, 1960). This supposition is
further supported by the density dependent mortality of advanced
larvae described earlier in this paper. It is suggested, therefore, that the
larvae are athulated to disperse by their encounters with other individuals; the higher the intensity of the mutual contact, the greater the
dispersion, probably up to a maximum (cf. p. 263).
H . KLOMP
disadvantage of still greater effect? The answer to this question will
necessarily be hypothetical, and is presented here merely as a suggestion.
Herrebout et al. (1963) have shown that the larvae of the pine looper
are highly camouflaged in their natural environment of pine needles as
a result of their colour pattern and habits of resting and feeding. Moreover, they have given strong arguments in favour of the view that the
fact of being camouflaged has functional significance, because it protects the insects against the attacks of enemies hunting by sight.
Referring to evidence from the literature the authors point out that the
effectiveness of the camouflage is increased by a solitary way of life:
“the longer the interval between encounters of an individual enemy
with specimens of the camouflaged prey, the more the experience
gathered by the enemy in a previous encounter will have waned before
the next takes place”. The same conclusion is reached by Brower (1958).
Furthermore, by comparing the effectiveness of the camouflage of
different pine inhabiting species, it was shown by Herrebout et al. that
the species with the most cryptic colour pattern also showed the best
adapted habits, and it was concluded that the different components of
the camouflage tend to vary in the same direction and amount, as if
being linked together.
The pine looper appears to have reached the most perfect degree of
concealment in both colour pattern and habits, and consequently it may
also be expected to have developed a mechanism to keep the larvae
separate and dispersed. This supposition is suggested by the fact that
the larvae of gregarious and aposematic species (Diprion p h i , Neodiprion sertifer) have developed special behaviour patterns to keep the
insects together (Prop, 1960).
Having reached this point we will return to the mutual interference
among larvae described in this paper. As reported earlier, the female
moth deposits the eggs in batches ranging from 2 to 25, with an average
of 6. Pine trees have a thin structure, with the twigs fairly well separated, and the pine looper larvae are rather inactive creatures. Consequently, the individuals of one batch might easily remain together for a
considerable period, when they are not stimulated to disperse. This will
be disadvantageous because enemies (birds) might readily learn that
having found one larva, some more will be present in the immediate
neighbourhood, and the predator might well develop a “searching
image” for such prey species (Tinbergen, 1960). This supposition is
further supported by the density dependent mortality of advanced
larvae described earlier in this paper. It is suggested, therefore, that the
larvae are athulated to disperse by their encounters with other individuals; the higher the intensity of the mutual contact, the greater the
dispersion, probably up to a maximum (cf. p. 263).