FEEDING INHIBITORS IN PEST CONTROL: EFECT OF HERB

POLISH JOURNAL OF ECOLOGY
(Pol. J. Ecol.)
52
4
575–581
2004
Short research contribution
Ma∏gorzata K¸YÂ
Pedagogical University, Institute of Biology,
Department of Ecology and Environment Protection,
Podbrzezie 3, 30-054 Kraków, Poland,
e-mail: [email protected]
FEEDING INHIBITORS IN PEST CONTROL: EFECT OF HERB
ADDITIONS TO FOOD ON THE POPULATION DYNAMICS
OF THE LESSER GRAIN BORER RHYZOPERTHA DOMINICA F.
(COLEOPTERA, BOSTRYCHIDAE).
ABSTRACT: The populations of Rhyzopertha dominica, a dangerous pest in stored grains
were investigated. This laboratory study
assumed the hypothesis that the introduction of
powdered leaves of Salvia officinalis L. and Artemisia absinthium L. containing feeding inhibitors
into grain may delay the development and therefore reduce population size of R. dominica.
These herbs were powdered and added at 0.5 g of
herb per 40 g wheat. The research was conducted in optimum conditions of temperature and
humidity (28ºC and relative humidity 60%).
The insects used in the experiment were initially obtained from mature individuals of uniform
age and were bred in glass containers with base
area 28 cm2 covered with gauze. The experiments were continued for 310 days and the herb
supplements were renewed each month. The
results of the study show that the introduction
of chemical substances contained in the powdered leaves of S. officinalis and A. absinthium
into an optimal substrate (wheat) infested with
R. dominica decreases its population size. These
substances have properties that inhibit the
feeding of this insect species.
KEY WORDS: Rhyzopertha dominica F.,
population dynamics, sex ratio, mortality, feeding inhibitors, powdered herbs
An important challenge in theoretical
and applied ecology is to find an effective
way to control granary and warehouse
pests. A major obstacle is the fact that the
application of chemical agents or the use of
biological methods using parasites or predators is not possible. Intensive research
programmes aimed at developing alternative methods to control these insects have
been performed (Boczek 1979, Ignatow i c z 1980b, H a g s t r u m et al. 1990,
L etellier et al. 1990, Collins et al. 2002).
Some methods modify the environmental
conditions, making them disadvantageous
for the pests, by regulating temperature
and humidity in storage facilities or by
introducing harmless chemical substances
such as feeding inhibitors, arrestants, repellents or attractants (L o s c h i a v o 1965,
Nawrot 1973,1983, Nawrot and Czaplicki 1978, Ignatowicz and Weso∏owska 1994a, b, K∏yÊ 1998).
Feeding inhibitors are chemical substances that discourage or prevent insects
from feeding by affecting their taste sensors. These compounds have no toxic
effects on the insects (Nawrot 1983).
Natural feeding inhibitors are usually alka-
576
Ma∏gorzata K∏yÊ
loids and glycosides occurring in wild or
cultivated plants. The mechanism of their
effect is complex and incompletely understood. It was found, however, that insects
exposed to them usually starved and ceased
to consume the nutritive material. This
resulted in a decrease of body weight or even
death if the feeding inhibitors were present
for a sufficient time. Exposure of larvae to
feeding inhibitors also resulted in metamorphic abnormalities and a loss of reproductive ability. (Wyrostkiewicz 1984).
The subject of this study was the lesser
grain borer, R. dominica, a destructive pest of
stored grain. This species is an indigent
warehouse pest and is included in the Polish
register of pests subject to mandatory eradication. This study assumed the hypothesis
that the introduction of powdered herbs
containing feeding inhibitors into grain
might retard development and therefore
reduce the population size of R. dominica.
Assessments of activity, development,
and population dynamics were made on
the basis of laboratory experiments. Wheat
was used as a substrate because of its
favourable qualities for the development of
R. dominica (Go∏´biowska and Nawrot
1976, Ciesielska 1978). The results of
the wheat-only variant were used as a control relative to the other experimental habitat – diet variants. In order to assess the
influence of certain herbal plants on pest
population dynamics, substrates of wheat
with common sage (Salvia officinalis L.) and
absinth sage-wort (Artemisia absinthium L.)
were used. These herbs were powdered and
added in a ratio of 0.5 g of herbs per 40 g of
wheat. All experimental colonies were started with 40 adult individuals, each sex being
represented in equal numbers and of the
same age, according to the method suggested by Ciesielska (1971, 1978). The
experimental variants were examined once
a month; at which time further substrate
was added in a fixed ratio of 0.5 g herbs to
40 g of grain, allowing the experiment to
continue for a long-term. The insects were
counted in sub-samples in glass containers
with base area 28 cm2 covered with gauze
or perforated containers to allow the circulation of air. The study was conducted in
the optimal thermal and moisture conditions of 28ºC and 60% RH. All variants
were repeated six times. Population dynamics assessments were based on population
sizes and rates of population growth, the
density of individuals in the batch, mortality and sex structure. The Chi-squared test
in Statistica v. 5.5 s. 999 – FGPJI – N4 was
used in statistical analysis.
After adding powdered common sage to
wheat, the population dynamics of R. dominica were characterised by low fluctuations
in size from the beginning until the 250th
day of development. The highest growth in
population size occurred between the 250th
and 340th day. At this time the population
size reached its highest level at over 500
individuals per batch (Fig. 1). On a wheat
substrate, the maximum population size was
attained at day 190. However, on wheat with
a common sage substrate the maximum size
was reached on day 340. The addition of
sage led to an almost 50% decline in the
maximum population size relative to the
control batch (with wheat substrate only,
Fig. 1). The population dynamics of R. dominica on the substrate composed of wheat and
sage-wort were characterized by two phases,
a phase of population growth between the
40th and 220th day of culture and a decline in
the population size from day 220 up to the
end of the experiment on day 310. A peak in
the population size was reached after 220
days (Fig. 1). Chi-squared analysis revealed
that differences between population size on
wheat substrate and wheat and herb (both
sage and sage-wort) substrate were highly
significant after the 70th experimental day.
Between the 40th and 220th day, the rate of
population growth exhibited almost cyclic
fluctuations. Already after 70 days a short-term decline in population growth could be
seen and a subsequent decline was apparent
between days 160–280.
The highest mortality at 64% after 220
days was noted on the wheat and sage substrate. Thereafter, the mortality rate
decreased over time to 20% (Fig. 2). The
addition of sage to substrate led to an
increase in mortality compared to the control substrate. The mortality rate in the
wheat and sage-wort substrate remained at
a relatively low level throughout the experiment, although, it increased during the final
two months to 25% and resulted in a decline
in population size (Fig. 2). The addition of
powdered sage to wheat did not influence
the sex ratio of the populations. The sex
ratio in the group of surviving individuals
was close to 1.0, which indicates an equal
number of males and females. A larger proportion of females (Y/X =0.8) was record-
577
Feeding inhibitors in pest control
almost always above 1, indicating a prevalence of males. However, the proportion of
the sexes was almost equal between days
160–220. During this period the population
reached its maximum size (Fig. 1).
Repellents, deterrents and feeding
inhibitors have been used for a long time in
pest eradication because the application of
ed after 40 experimental days. In the final
phase of population development, the proportion of males increased (Y/X >1), and
this correlated with a population decline
(Fig. 3). The sex ratio among dying individuals fluctuated between 0.3–0.9 indicating
a high mortality of females (Fig. 4). In
wheat with sage-wort, the sex ratio was
number of individuals in culture
1000
800
600
400
200
0
0
30
60
90
wheat
120
150 180
days
210
wheat and sage
240
270
300
330
wheat and sage-wort
Fig. 1. Comparision of population dynamics of Rhyzopertha dominica in different habitat and diet
conditions.
70
60
50
40
%
30
20
10
0
40
70
100
130
160
190
220
250
280
310
days
wheat
wheat and sage-wort
wheat and sage
Fig. 2. Per cent of dead individuals in populations of Rhyzopertha dominica in different habitat and
diet conditions.
578
Ma∏gorzata K∏yÊ
chemical substances in granaries and warehouses is very limited. Therefore, it is important to understand the effect of biotic and
abiotic factors and their combined influence
on regulating population size in pests
(W h i t e et al. 1983, C i e s i e l s ka 1992,
1994, Ciesielska and K∏yÊ 2002). This is
the basis of formulating effective protection
programmes against pests in which an ever
larger role is assigned to plant-based substances (Boczek 1983, Baker and L os c h i a v o 1987). Studies concerning the
influence of feeding inhibitors on foraging in
herbivorous insects have demonstrated that
2.0
1.8
sex ratio
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
30
60
90
wheat
120
150 180
days
210
wheat and sage
240
270
300
330
wheat and sage-wort
Fig. 3. Comparision of sex ratios in Rhyzopertha dominica in different habitat and diet conditions
(individuals live).
1.4
1.2
sex ratio
1.0
0.8
0.6
0.4
0.2
0
0
30
60
wheat
90
120
150 180
days
wheat and sage
210
240
270
300
330
wheat and sage-wort
Fig. 4. Comparision of sex ratios in Rhyzopertha dominica in different habitat and diet conditions
(individuals dead).
579
Feeding inhibitors in pest control
individuals often fasted after consuming
plants treated with antifeedants (Wyrostkiewicz 1984). Nawrot (1973, 1983) studied the effects of feeding attractants and
repellents on the grain weevil Sitophilus
granarius L. He demonstrated that barley
groats, moist wheat grain and wheat and rye
plumules were the most effective attractants
for imagines. However, an alcohol extract
from plumules of wheat and rye acted as
a repellent. In further studies, Nawrot and
Czaplicki (1978) showed that S. granarius
imagines locate food by chemoreception and
react to triglycerides in plumules. This was
further confirmed by Tamaki and L oschiavo (1971) and Tamaki et al. (1971)
who established the attractive potential of
unsaturated triglycerides for Tribolium confusum Duv. Furthermore, mineral salts influence viability, life expectancy and reproduction
in S. granarius and Tyrophagus putrescentiae
Schrank (Ignatowicz 1979, 1980a and b).
The latter author demonstrated that S. granarius has a high tolerance for excessive
levels of inorganic salts. Nevertheless, substances with trace elements such as J, F and
Hg caused high mortality. Potassium iodine
causes a decrease in fertility in S. granarius.
The mould mite, T. putrescentiae is relatively
insensitive to an excess of calcium phosphate in its diet. Even at a high concentration complete inhibition of fertility or high
mortality was not recorded.
B a n a s i k and I g n a t o w i c z (1995)
assessed the effects of certain species of
powdered plants (called plant powders by
these authors) for repelling or attracting
individuals of S. granarius and Sitophilus oryzae L. and found that the repellent effect of
the powders was increased when their concentration was raised in wheat grain. As
effective repellents they suggest powdered
tansy (Tanacetum vulgare L.), sweet clover
(Melilotus officinalis L.), yarrow (Achillea
millefolium L.) and purple deadnettle
(Lamium purpureum L.).
This study aimed at describing changes
in the population dynamics of R. dominica
when sage and sage-wort were added to its
environment (and diet). The results show
that the addition of chemical substances
found in powdered sage and sagewort into
R. dominica substrates causes a decline in
population size in this species. These substances act as feeding inhibitors for this
insect. Sage is particularly effective at slowing population growth and the number of
individuals is kept at a low level. The total
population size is four times lower compared
to the size of control populations on a wheat
substrate. Only the maximum population
size is significantly lower in case of the addition of sage-wort . The maximum population size, as in the case of sage, is almost half
the maximum population size of those kept
on pure wheat. Moreover, the addition of
sage-wort causes the population’s sex ratio to
shift in favour of males and in effect evens
out the sex ratio. This is expressed in the
value of the index oscillating around 1, while
in wheat it is less than 1. An increase in this
value takes place by reason of greater female
mortality. It may be presumed that females
are more susceptible to the effects of feeding
inhibitors.
The results obtained demonstrate
that:
1. The addition of powdered herbs S. officinalis and A. absinthium to an optimal substrate for R. dominica causes a decline in
the population size of this pest species.
2. Chemical substances found in S. officinalis and A. absinthium possess feeding
inhibitors properties for R. dominica.
3. The addition of sage-wort to a wheat substrate causes the sex structure to shift in
favour of males. Moreover, the addition of
herbs to the wheat substrate increases
female mortality. It may be presumed
that females are more susceptible to the
effects of feeding inhibitors.
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(Received after revising May 2004)