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Russian Journal of Ecology, Vol. 34, No. 5, 2003, pp. 350–354. Translated from Ekologiya, No. 5, 2003, pp. 387–391.
Original Russian Text Copyright © 2003 by Ponomarev.
An increase in the survival rate of the larvae of nee-
dle- or leaf-gnawing insects and, hence, in their popu-
lation density is often attributed to the weakening of
physiological activity of their host plants and an
increase in the protein and carbohydrate contents in
their foliage, which are favorable for the larvae. The
food quality (assimilability) of leaves for the same spe-
cies (the gypsy moth) sometimes directly correlates
with the contents of free sugars in the leaf; in other
cases, however, this correlation may be absent or
inverse (Benkevich, 1984; Meyer and Montgomery,
1987). The data concerning proteins are also contradic-
tory (Meyer and Montgomery, 1987; Facth, 1992).
Moreover, the contents of nitrogen-containing com-
pounds in the leaves decreases most rapidly in droughty
years, which usually coincide with pest population out-
breaks, while an increase or ﬂuctuations in the content
of nitrogen result in its lower assimilation by the larvae
(Stockhoff, 1993). According to Feeny (1970), the sur-
vival of leaf-gnawing insects depends on the age of
leaves and the contents of water and tannins in them.
On the other hand, Haukioja and Niemela (1978) pos-
tulated that phenols are the main factor of plant protec-
tion from defoliation by pests. However, numerous sub-
sequent studies on the effects of phenols on the devel-
opment of leaf-gnawing insects produced contradictory
results, which made Haukioja (1989) reject the former
hypothesis and suppose that the role of carbohydrate
content in the leaves is probably more important.
Edel’man (1963) considered the data indicating that
the early- and late-instar larvae of spring- and summer-
feeding leaf-gnawing insects, including the gypsy
moth, differ in their requirements for the biochemical
composition of food (in particular, the contents of nitro-
gen-containing compounds and carbohydrates). On this
basis, she concluded that “the coincidence of seasonal
changes in the biochemical composition of food and the
dietary requirements of insects at all stages of their
development is one of the factors responsible for pest
population outbreaks” (Edel’man, 1963, p. 12). This
postulate deserves serious consideration.
All other factors (morbidity, developmental abnor-
malities, etc.) being equal, the survival rate of the larvae
consuming a certain kind of food must be dependent on
one more factor, namely, the positive balance of energy
and matter upon feeding. When the content of carbohy-
drates in the foliage is low, nothing except for one fac-
tor can prevent a larva from consuming more food to
obtain the necessary amount of carbohydrates. This
factor is the energy cost of food assimilation.
In this context, attention should be paid to such a
parameter as pH of the leaf homogenate of a food plant.
It is known that acidity of the leaf sap increases in the
period from the opening of leaves to their full maturity
and, thereafter, decreases with age, and the shape of the
acidity curve depends on both plant species and envi-
ronmental conditions (Vasﬁlov, 1997).
The formation of protein–tannin complexes upon
destruction of vacuoles in the leaf creates a problem for
pests feeding on foliage. This phenomenon has given
rise to the concept that tannins have a role in plant pro-
tection from defoliation (Schultz and Lechowicz,
1986). However, the gypsy moth prefers to feed on the
plants whose foliage contains great amounts of tannins,
such as species of the families Salicaceae, Betulaceae,
and Fagaceae (Benkevich, 1984). In the experiments
performed by American researchers (Govenor
1997), the larvae whose food contained tannins and had
a high pH value proved to reach a greater weight while
consuming less food than the larvae that were on a tan-
The protein–tannin complexes form in an acidic
medium and decompose at pH > 9 (Schultz and
Lechowicz, 1986). Alkalization of the midgut contents
is dependent on oxidative phosphorylation and occurs
Physiological Age of Host Plant Foliage and Survival
of Gypsy Moth Larvae
V. I. Ponomarev
Botanical Garden, Ural Division, Russian Academy of Sciences, ul. Bilimbaevskaya 32a, Yekaterinburg, 620134 Russia
Received December 27, 2002
—The pH of leaf homogenates of common birch (
L.), a food plant of gypsy moth
L.) larvae, was measured at different times of day in the course of leaf organogenesis, and
midgut pH was measured in gypsy moth larvae phenotypically differing in the color of the hypodermis at the
ﬁfth instar. A possible relation between these parameters is discussed.
: gypsy moth, pH of food plant leaves, midgut pH in larvae.