Suhling et al. - 2000 - Effects of insecticide applications on macroinvert

Hydrobiologia 431: 69–79, <strong>2000</strong>.
H.L. Golterman (ed.), Sediment–Water Interaction 10.
© <strong>2000</strong> Kluwer Academic Publishers. Printed in the N<strong>et</strong>herlands.
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<strong>Effects</strong> <strong>of</strong> <strong>insecticide</strong> <strong>applications</strong> on macroinvertebrate density
and biomass in rice-fields in the Rhône-delta, France
Frank <strong>Suhling</strong> 1 , Silke Befeld 2 , Matthias Häusler 1 , Katrin Katzur 1 , Sigrit Lepkojus 1
& Francois Mesléard 2
1 Zoologisches Institut, Technische Universität Braunschweig, Fasanenstraße 3, D-38092 Braunschweig, Germany
2 Station Biologique de la Tour du V<strong>al</strong>at, Le Sambuc, F-13200 Arles, France
Received 2 March 1999; in revised form 10 June 1999; accepted 20 June 1999
Key words: rice-fields, lindane, diazinon, <strong>al</strong>pham<strong>et</strong>hine, macroinvertebrate succession, Odonata
Abstract
The density <strong>of</strong> 23 macroinvertebrate species and the tot<strong>al</strong> macroinvertebrate biomass were compared b<strong>et</strong>ween
rice-fields treated with lindane and diazinon in June and <strong>al</strong>pham<strong>et</strong>hine in August and untreated controls. The
macroinvertebrates could be divided into four groups: (1) Taxa, in which the densities were lower in the <strong>insecticide</strong>
treatment in July and August than in the non-<strong>insecticide</strong> treatment. (2) The Culicidae which occurred in
the <strong>insecticide</strong> treatment in significantly lower density in July, but in significantly higher density in August. (3)
Ischnura elegans (Vander L.) which was found in July after the lindane application in significantly higher numbers
in the <strong>insecticide</strong> treatments, but in significantly lower numbers in the <strong>insecticide</strong> treatment in August after the
application <strong>of</strong> the pyr<strong>et</strong>hroid. In these three groups, we assumed that direct effects due to the <strong>insecticide</strong>s toxicity
were the reason for the differences in density. (4) The fourth group included three taxa in which the densities were
significantly higher in the <strong>insecticide</strong> treatment in July and August than in the control. For this, indirect effects
due to reduced biotic interactions may be responsible. The biomass was higher in the <strong>insecticide</strong> treatments in
July, mainly because <strong>of</strong> a high increase in gastropod density, during the rest <strong>of</strong> the season it was similar b<strong>et</strong>ween
treatments and controls.
Introduction
For aquatic anim<strong>al</strong>s, rice-fields are extreme habitats
with respect to the abiotic conditions (Fernando,
1993). In many physic<strong>al</strong> and chemic<strong>al</strong> param<strong>et</strong>ers,
like water temperature, O 2 concentration and particularly
the duration <strong>of</strong> flooding, they are comparable
to typic<strong>al</strong> temporary waters and the invertebrates need
speci<strong>al</strong> adaptations to survive these conditions (Williams,
1987). Like natur<strong>al</strong> temporary w<strong>et</strong>lands, the
rice-fields are characterised by a typic<strong>al</strong> cycle <strong>of</strong> flooding
and desiccation, leading to a strong succession in
their fauna (Heckman, 1974, 1979).
Rice-fields in the Mediterranean region differ in
some respects from natur<strong>al</strong> temporary w<strong>et</strong>lands in
the same region. (1) They have an aperiodic water
cycle with respect to the rainy season: whereas
Mediterranean natur<strong>al</strong> temporary w<strong>et</strong>lands are dry in
summer, rice-fields are dry in winter. This difference
may cause problems for those species whose
life-cycles are adapted to natur<strong>al</strong> temporary w<strong>et</strong>lands,
e.g. some dragonflies whose larv<strong>al</strong> stages occur during
winter and which are adult and, therefore, independent
<strong>of</strong> water, during the dry season (Aguesse, 1960;
Samraoui <strong>et</strong> <strong>al</strong>., 1998). (2) Agricultur<strong>al</strong> operations
associated with rice-farming, including pesticide application,
soil fertilisation and ploughing, may affect
macroinvertebrates and prevent the colonisation <strong>of</strong>
rice-fields by some species (Aguesse, 1960; Takamura
& Yasuno, 1985; Kurihara, 1989; Simpson <strong>et</strong> <strong>al</strong>.,
1994a, b). Insecticides which reduce insect pests reducing
the yield like planthoppers (Cicadidae), leafhoppers
(Orthopteroidea), bugs (H<strong>et</strong>eroptera), moths
(Lepidoptera) and chironomids (Diptera) (Kiritani,
1979; Way <strong>et</strong> <strong>al</strong>., 1991; Cohen <strong>et</strong> <strong>al</strong>., 1994; Way &
Heong, 1994) and mosquitoes (Meek & Olson, 1991)

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particularly affect a shift in macroinvertebrate community
structures because <strong>of</strong> their selective effects on
different species. According to Takamura & Yasuno
(1985), the densities <strong>of</strong> predators, aquatic be<strong>et</strong>les and
dragonflies in a Japanese rice-field decreased due to
pesticide application, while that <strong>of</strong> chironomids and
ostracods increased (for the latter see <strong>al</strong>so Simpson <strong>et</strong>
<strong>al</strong>., 1994b).
The invertebrate fauna <strong>of</strong> Mediterranean rice-fields
in the Rhône and the Ebro deltas is well known.
Some studies de<strong>al</strong> with microcrustacea (Pont, 1977,
1985), others provide data on the macroinvertebrates
(Aguesse, 1960; Tourenq, 1966, 1970; Marazan<strong>of</strong>,
1969; Vi<strong>al</strong>a, 1978; Pont & Vaquer, 1986; González-
Solís & Ruiz, 1996). However, few studies de<strong>al</strong> with
the effects <strong>of</strong> <strong>insecticide</strong>s on the invertebrate fauna
(e.g. Schnapauff, 1995). The aim <strong>of</strong> this study was
to d<strong>et</strong>ect the impact <strong>of</strong> <strong>insecticide</strong> application on the
macroinvertebrate biomass and density in the ricefields
<strong>of</strong> the Rhône delta, with some speci<strong>al</strong> reference
to odonate populations.
Study area
The study was carried out at the domaine Tour du
V<strong>al</strong>at / P<strong>et</strong>it Badon (43 ◦ 31 ′ N, 4 ◦ 40 ′ E) which is
situated in the Rhône delta (South <strong>of</strong> France). For further
d<strong>et</strong>ails on the domaine, see Sinnassamy & Pineau
(1996). Rice farming was developed in the Camargue
after the second world war. The area under riziculture
peaked at about 32 000 ha in 1960, but socio-economic
changes beginning in 1963 reduced this to 4000 ha
by 1980 (Barbier & Mour<strong>et</strong>, 1992). After 1981, EC
subsides and improved agricultur<strong>al</strong> techniques led to
an increase <strong>of</strong> the farming area which reached 24 000
ha in 1997 (16% <strong>of</strong> the tot<strong>al</strong> area <strong>of</strong> the Camargue).
Another 26 000 ha were covered by dry crops. Sixty
thousand ha were occupied by natur<strong>al</strong> habitats including
marshes and lagoons, and 25 000 ha by s<strong>al</strong>t
pans.
Materi<strong>al</strong> and m<strong>et</strong>hods
Experiment<strong>al</strong> rice-fields
To study the effects <strong>of</strong> <strong>insecticide</strong> application on the
aquatic macroinvertebrate community and biomass experiment<strong>al</strong>
rice-fields were s<strong>et</strong> up in January 1997
using existing rice-fields. No pesticides were used in
these fields the preceding 10 years. The study site consisted
<strong>of</strong> 18 fields <strong>of</strong> 0.38 ha each. The fields were
separated by dikes and irrigated with water from a
nearby can<strong>al</strong> at 3 day interv<strong>al</strong>s. The water arrived at
an inflow area, which was <strong>al</strong>so sown with rice, and
from there was distributed to the fields by pipes in the
dikes. At the end <strong>of</strong> January, the fields were drained
and ploughed and harrowed before sowing on May 13.
The experiment included two different treatments,
each <strong>of</strong> nine rice-fields, varying the factor <strong>insecticide</strong>
application. On June 19, Icazon (175 g l −1 lindane and
50 g l −1 diazinon active ingredients) in a concentration
<strong>of</strong> 1 l ha −1 was applied in a dilution with water (400
lha −1 ) directly to the flooded surface <strong>of</strong> nine fields
to combat leaf-mining chironomids. With a maximum
mean water level <strong>of</strong> 15 cm the concentrations <strong>of</strong> the
active ingredients were c<strong>al</strong>culated to be 116.7 µg l −1
lindane and 33.3 µgl −1 diazinon. On August 7, Fastac
(<strong>al</strong>pham<strong>et</strong>hine, a pyr<strong>et</strong>hroid) in a concentration <strong>of</strong> 3
lha −1 was applicated to control Chilo suppress<strong>al</strong>is
(Lepidoptera) in a dilution with heliosol (terpen <strong>al</strong>cohol)
0.3 l ha −1 as a fixative and water 500 l ha −1 .The
concentration <strong>of</strong> <strong>al</strong>pham<strong>et</strong>hine at 15 cm water level
was c<strong>al</strong>culated to be 10 µg l −1 . The adsorption <strong>of</strong> the
<strong>insecticide</strong>s to the sediment – which may occur within
a few days (Thybaud, 1990) – was not c<strong>al</strong>culated. No
fertilisers, herbicides or fungicides were used. In addition
to rice (Oryza sativa, var.Cig<strong>al</strong>on)Echinocloa
crus-g<strong>al</strong>li (L.), Cyperus ssp., Polygonium amphibium
L., Scirpus maritimus L., H<strong>et</strong>eranthera limosa and
Characeae grow in the fields. The fields were drained
1 week before harvesting on September 24 and 25.
Macroinvertebrate sampling
To obtain data on macroinvertebrate density and biomass,
quantitative samples were taken using a squaresampler.
Three sides <strong>of</strong> the sampler were closed
with mesh (1.3 mm) and the remaining side with the
sampling n<strong>et</strong> (mesh size: 0.5 mm). The inner area <strong>of</strong>
the sampler was 0.325 × 0.325 m (0.1 m 2 ). The frame
<strong>of</strong> the sampler was placed over a randomly chosen plot
<strong>al</strong>ong a transect (see below) and the veg<strong>et</strong>ation in the
inner frame was cut and, tog<strong>et</strong>her with the sediment,
pushed into the n<strong>et</strong> using a sm<strong>al</strong>l broom. Then the
sampler was lifted out <strong>of</strong> the water and the sediment
transferred to a white bowl and manu<strong>al</strong>ly searched for
the macr<strong>of</strong>auna. The invertebrate samples were preserved
with 70% Ethanol in 5 ml jars and identified
to the species in the laboratory. The sampling started
just after the flooding <strong>of</strong> the fields in May, 1997.

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The sampling periods were: (I) 13–17 May, 1997; (II)
17–19 June, 1997; (III) 16–19 July, 1997 and (IV)
21–23 August, 1997. During each sampling period,
four samples were taken per field <strong>al</strong>ong a transect <strong>of</strong>
20 m, so that the number <strong>of</strong> samples per treatment and
sampling period was 36.
Biomass
Biomass measurements using preserved materi<strong>al</strong> usu<strong>al</strong>ly
suffers from weight loss <strong>of</strong> the organisms due
to the dissolution <strong>of</strong> fatty acids <strong>et</strong>c. in <strong>al</strong>cohol (e.g.
Schwoerbel, 1986). To minimise this problem, the following
m<strong>et</strong>hod was used: before being filled, the jars
used for preservation <strong>of</strong> the macroinvertebrate samples
were weighed to the nearest 0.001 g using a M<strong>et</strong>tlerb<strong>al</strong>ance
(precision: 0.0001 g) and numbered. In the
laboratory, the <strong>al</strong>cohol was vaporised and the samples
dried at 60 ◦ C for 72 h in the jars, which were then
weighed again. Using this m<strong>et</strong>hod, <strong>al</strong>l dissolved materi<strong>al</strong>
remained in the jars after drying. The difference
in weight b<strong>et</strong>ween the empty jar and the jar with the
dried organisms was considered the dry biomass per
sample.
Odonate emergence
In addition to sampling, the effect <strong>of</strong> <strong>insecticide</strong> application
was studied by monitoring odonate emergence
in 12 fields. The anisopteran exuviae were
collected <strong>al</strong>ong 16 m transects at 2-day interv<strong>al</strong>s and
counted and identified in the lab. To g<strong>et</strong> quantitative
data on zygopteran emergence, in which exuviae were
much harder to d<strong>et</strong>ect, cages with an area <strong>of</strong> 0.8 m
× 0.8 m were placed close to the edges <strong>of</strong> six fields
treated with <strong>insecticide</strong>s and six untreated fields. The
damselflies emerging in the cages were recorded at
2-day interv<strong>al</strong>s, and identified.
Data an<strong>al</strong>ysis
Sampling data on the densities <strong>of</strong> these taxa, as well as
on biomass, were an<strong>al</strong>ysed using two-way ANOVAs
with the sampling date and the <strong>insecticide</strong> application
/ non-application as independent variables. In those
taxa where the ANOVAs indicated significant effects
<strong>of</strong> <strong>insecticide</strong> application or significant interactions <strong>of</strong>
date and <strong>insecticide</strong> application, a posteriori an<strong>al</strong>yses’
on means were used to d<strong>et</strong>ermine monthly differences
in the effects <strong>of</strong> <strong>insecticide</strong> application. The data
on anisopteran and zygopteran emergence were com-
Table 1. Results <strong>of</strong> 2-way ANOVAs for the effects <strong>of</strong> date and
<strong>insecticide</strong> application on the density <strong>of</strong> selected species. ∗ = P
≤ 0.05, ∗∗ = P ≤ 0.01, ∗∗∗ = P ≤ 0.001
Taxon
ANOVA F-v<strong>al</strong>ue for
Date Insecticide Insect. × Date
(DF=3) (DF=1) (DF=3)
Gyraulus chinensis 17.780 ∗∗∗ 14.649 ∗∗∗ 6.122 ∗∗∗
Physella acuta 5.565 ∗∗ 1.613 0.432
Oligocha<strong>et</strong>a 7.992 ∗∗∗ 2.642 0.310
Erpobdella octoculata 13.526 ∗∗∗ 6.737 ∗ 5.297 ∗∗
Hydrachnellae 12.648 ∗∗∗ 0.984 0.940
Caënis sp. 13.815 ∗∗∗ 3.553 7.505 ∗∗∗
Cloëon dipterum 14.415 ∗∗∗ 9.074 ∗∗ 9.679 ∗∗∗
Baëtis sp. 7.835 ∗∗∗ 2.667 4.532 ∗∗
Ischnura elegans 32.412 ∗∗∗ 5.783 ∗ 15.149 ∗∗∗
Orth<strong>et</strong>rum <strong>al</strong>bistylum 7.257 ∗∗∗ 1.029 0.825
Orth<strong>et</strong>rum cancellatum 9.255 ∗∗∗ 7.230 ∗∗ 3.437 ∗
Crocothemis erythraea 25.300 ∗∗∗ 0.303 0.366
Symp<strong>et</strong>rum fonscolombii 21.150 ∗∗∗ 6.703 ∗ 3.650 ∗
Corixa punctata 1.709 2.831 1.324
Sigara later<strong>al</strong>is 2.660 1.560 1.526
carnivorous H<strong>et</strong>eroptera 7.044 ∗∗∗ 12.195 ∗∗∗ 5.639 ∗∗
Culicidae 15.512 ∗∗∗ 0.330 7.148 ∗∗∗
Chironomidae 7.700 ∗∗∗ 1.239 0.699
Berosus ssp. 7.557 ∗∗∗ 2.027 3.669 ∗
Guignatus pusillus 1.740 0.058 2.662
H<strong>al</strong>iplinus heydeni 6.218 ∗∗∗ 3.158 5.583 ∗∗
Laccophilus sp. 24.576 ∗∗∗ 10.745 ∗∗ 6.921 ∗∗∗
Noterus sp. 19.243 ∗∗∗ 6.263 ∗ 4.324 ∗∗
bined from <strong>al</strong>l six transects and cages, respectively, per
treatment and an<strong>al</strong>ysed with chi 2 -test.
Only species numbering in at least 30 individu<strong>al</strong>s
during <strong>al</strong>l sampling periods tog<strong>et</strong>her were an<strong>al</strong>ysed. In
some cases, when exact identification <strong>of</strong> the species
was not possible, taxa were pooled for further an<strong>al</strong>ysis.
This occurred with the Chironomidae (at least four
species), the Culicidae (at least three species), the Hydrachnellae
(four species) and Berosus spp. (= Berosus
luridens (L.) and B. signaticollis (Charp.)). Carnivorous
H<strong>et</strong>eroptera (= Naucoris maculatus Fabr., Nepa
cinerea L., Notonecta glauca L. and Plea minutissima
Leach) are numbered <strong>al</strong>l below 30 but <strong>al</strong>l showed
the same distribution, so these were <strong>al</strong>so pooled.
In some pairs <strong>of</strong> odonates – Orth<strong>et</strong>rum cancellatum
(L.) and O. <strong>al</strong>bistylum (Sélys), Crocothemis erythraea
(Brullé) and Symp<strong>et</strong>rum fonscolombii (Sélys),
Ischnura elegans (Vander. L.) and I. pumilio (Charp.)
– sm<strong>al</strong>l larvae (below instar 7) could not be correctly

72
classified. The same was true <strong>of</strong> the corixid larvae.
Consequently sm<strong>al</strong>l odonate larvae and corixid larvae
were excluded from the an<strong>al</strong>ysis.
Results
<strong>Effects</strong> <strong>of</strong> sample date
A tot<strong>al</strong> <strong>of</strong> 84 species <strong>of</strong> macroinvertebrates was found
in the experiment<strong>al</strong> rice-fields. In May, 18 taxa were
found and the number increased to 40 in June and 56
in July, decreasing slightly in August to 53. In most <strong>of</strong>
the taxa, fewer than 30 individu<strong>al</strong>s were caught during
the sample periods. Twenty-three taxa were found in
abundance <strong>al</strong>lowing a statistic<strong>al</strong> comparison <strong>of</strong> the effects
<strong>of</strong> sample period and <strong>insecticide</strong> application on
densities. With the exception <strong>of</strong> the be<strong>et</strong>le Guignatus
pusillus (Fabr.) and the bugs Corixa punctata (Illiger)
and Sigara later<strong>al</strong>is (Leach) the densities <strong>of</strong> <strong>al</strong>l <strong>of</strong>
these 23 taxa varied significantly with the sample dates
(Table 1). Only the oligocha<strong>et</strong>es and the chironomids
reached their greatest abundance in May and June, respectively
(see Table 2). Gyraulis chinensis (Dunker),
Ba<strong>et</strong>is sp., Berosus ssp., Laccophilus sp. and the Hydrachnellae
were found in their highest densities in
July and <strong>al</strong>l the others occurred mainly in August,
particularly carnivorous species such as odonates and
some bugs (Notonecta, Naucoris).
Insecticide application and macroinvertebrate density
In nine <strong>of</strong> the 23 taxa an<strong>al</strong>ysed, no significant effects
<strong>of</strong> the treatment (<strong>insecticide</strong> application / non application)
were found (Table 1). These were Physella acuta
(Drap.), Oligocha<strong>et</strong>a, Hydrachnellae, Orth<strong>et</strong>rum <strong>al</strong>bistylum
(Sélys), Crocothemis erythraea (Brullé), C.
punctata, S. later<strong>al</strong>is, Chironomidae and G. pusillus.
In 14 taxa, two-way ANOVAs indicated significant effects
<strong>of</strong> the treatment and / or significant treatment ×
date interactions on density (see Table 2). We should
keep in mind that the first <strong>insecticide</strong> application was
carried out after the second sample period, so, differences
in density b<strong>et</strong>ween treatments not should
be expected before the sample period in July. Consequently
the macroinvertebrates may be divided into
four categories:
1. Taxa in which the densities were gener<strong>al</strong>ly lower
in the <strong>insecticide</strong> treatments than in the untreated
samples following the first <strong>insecticide</strong> application
in June, and significantly in at least 1 month.
This group includes three ephemeropterans (Ba<strong>et</strong>is
sp., Cloeon dipterum (L.), Caenis sp.), two
odonates (Orth<strong>et</strong>rum cancellatum (L.), Symp<strong>et</strong>rum
fonscolombii (Sélys)), the carnivorous H<strong>et</strong>eroptera
and three coleopterans (Berosus spp., H<strong>al</strong>iplinus
heydeni Wehnke, Noterus sp.) (see Table 2).
2. The Culicidae which occurred in significantly
lower density in the <strong>insecticide</strong> than in the non<strong>insecticide</strong>
treatment following the Icazon application
in June but in significantly higher density
following the Fastac application in July (Table 2).
3. Ischnura elegans (Vander L.) which, in contrast,
was found in significantly higher numbers in July
after the application <strong>of</strong> Icazon in the <strong>insecticide</strong>
treatment, but in significantly lower numbers in
August after the application <strong>of</strong> the pyr<strong>et</strong>hroid
(Table 2).
4. The fin<strong>al</strong> group includes Gyraulus chinensis
(Dunker), Erpobdella octoculata (L.) and Laccophilus
sp., in which the densities were higher in the
<strong>insecticide</strong> treatment than in the non-<strong>insecticide</strong>
treatment in July and August.
Results from odonate emergence versus sampling
A tot<strong>al</strong> <strong>of</strong> eleven species <strong>of</strong> odonates occurred in the
fields, and in 10 <strong>of</strong> these emergence was registered
(Table 3). Results from the emergence studies differed
in one aspect from those derived from sampling: in
I. elegans, there was no significant difference in the
number <strong>of</strong> emerged individu<strong>al</strong>s b<strong>et</strong>ween the two treatments
(Table 3). However, in the emergence <strong>of</strong> Anisoptera,
the results resemble those from the sampling:
exuviae <strong>of</strong> S. fonscolombii and O. cancellatum were
found in significantly higher numbers in fields without
<strong>insecticide</strong>s.
Macroinvertebrate community: biomass, density,
diversity
Tot<strong>al</strong> macroinvertebrate biomass and density increased
from May to July (Figure 1). In July both biomass
and tot<strong>al</strong> density were significantly higher in the
<strong>insecticide</strong>-treated fields than in the untreated fields.
In this month we found the maximum mean biomass
(dry weight) <strong>of</strong> about 3 g m −2 . In the other months
there were no significant differences. From July to August,
there was no increase in either param<strong>et</strong>er except
<strong>of</strong> the biomass in the untreated fields where it reached
its maximum mean v<strong>al</strong>ue in August.
To compare the community diversities b<strong>et</strong>ween the
sample dates and the <strong>insecticide</strong>-treated and untreated

73
Table 2. Density <strong>of</strong> macroinvertebrate taxa (individu<strong>al</strong>s per m 2 ± SD) in rice-fields with and without
<strong>insecticide</strong> application. For each taxon, only those months are given when the species was present. N is
the tot<strong>al</strong> number <strong>of</strong> individu<strong>al</strong>s per taxon and month. A posteriori an<strong>al</strong>ysis: ∗ = P ≤ 0.05, ∗∗ = P ≤ 0.01
Taxon Sample- N Density m −2 [± SD] in rice-fields P
period With <strong>insecticide</strong>s Without <strong>insecticide</strong>s
Gyraulus chinensis May 31 2.8 ± 3.4 5.8 ± 3.3
June 3057 394.2 ± 215.6 455.0 ± 455.6
July 5644 1122.8 ± 524.6 445.0 ± 281.1 ∗∗
August 3717 800.2 ± 453.2 238.6 ± 187.4 ∗∗
Physella acuta June 95 24.7 ± 38.1 1.7 ± 4.1
July 789 181.9 ± 284.1 43.3 ± 41.2
August 1251 283.9 ± 333.0 203.1 ± 365.2
Oligocha<strong>et</strong>a May 1378 174.7 ± 162.8 208.1 ± 159.9
June 125 6.7 ± 12.2 28.1 ± 66.8
July 203 9.7 ± 12.9 46.7 ± 92.8
August 463 19.6 ± 34.6 111.7 ± 219.8
Erpodella octoculata May 3 0.3 ± 0.8 0.6 ± 1.1
June 17 2.5 ± 4.5 3.6 ± 6.1
July 52 9.4 ± 14.0 5.0 ± 8.2
August 180 40.3 ± 30.7 11.1 ± 11.1 ∗
Hydrachnellae May 1 0.0 ± 0.0 0.3 ± 0.8
June 6 1.4 ± 2.5 0.3 ± 0.8
July 44 5.0 ± 5.4 7.2 ± 5.9
August 8 0.3 ± 0.8 1.9 ± 3.5
Ba<strong>et</strong>is sp. June 15 3.9 ± 4.7 0.3 ± 0.8 ∗
July 37 7.2 ± 5.4 3.1 ± 4.3
August 12 0.3 ± 0.8 3.1 ± 3.7 ∗
Caenis sp. June 127 31.4 ± 25.4 3.9 ± 4.5 ∗
July 68 6.9 ± 10.6 11.9 ± 10.2
August 576 32.6 ± 24.8 129.7 ± 112.3 ∗
Cloeon dipterum July 1 0.3 ± 0.8 0.0 ± 0.0
August 42 1.4 ± 4.2 13.1 ± 10.5 ∗
Ischnura elegans July 57 11.1 ± 8.4 4.7 ± 3.2 ∗
August 134 8.1 ± 8.8 29.4 ± 13.9 ∗∗
Orth<strong>et</strong>rum <strong>al</strong>bistylum July 7 0.8 ± 2.5 1.1 ± 1.3
August 32 3.2 ± 8.8 6.4 ± 4.4
Orth<strong>et</strong>rum cancellatum July 6 0.0 ± 0.0 1.9 ± 3.5
August 29 1.7 ± 3.5 6.9 ± 6.8 ∗
Crocothemis erythraea July 43 5.3 ± 8.0 6.7 ± 5.4
August 620 100.4 ± 98.7 79.7 ± 35.5
Continued on p. 74

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Table 2. Continued
Taxon Sample- N Density m −2 [± SD] in rice-fields P
period With <strong>insecticide</strong>s Without <strong>insecticide</strong>s
Symp<strong>et</strong>rum June 1 0.3 ± 0.8 0.0 ± 0.0
fonscolombii July 23 0.8 ± 1.3 6.1 ± 8.8
August 152 12.4 ± 13.9 29.4 ± 19.9 ∗
Corixa punctata June 24 0.8 ± 1.8 5.8 ± 11.2
July 7 1.1 ± 3.3 0.8 ± 2.5
August 9 0.0 ± 0.0 2.5 ± 4.5
Sigara later<strong>al</strong>is May 3 0.8 ± 1.8 0.0 ± 0.0
June 33 1.7 ± 2.5 7.5 ± 13.8
July 5 0.8 ± 1.8 0.6 ± 1.1
August 5 0.0 ± 0.0 1.4 ± 3.3
Carnivorous H<strong>et</strong>eroptera July 9 0.3 ± 0.8 2.2 ± 3.8
August 20 0.3 ± 0.8 5.3 ± 4.4 ∗∗
Culicidae June 3 0.8 ± 1.8 0.0 ± 0.0
July 26 1.1 ± 1.8 6.1 ± 4.4 ∗∗
August 51 10.1 ± 7.1 4.2 ± 2.5 ∗
Chironomidae May 1918 405.0 ± 161.2 127.8 ± 70.8
June 4576 637.8 ± 300.1 633.3 ± 830.9
July 1287 162.8 ± 162.0 194.7 ± 213.8
August 771 182.1 ± 338.4 60.8 ± 35.6
Berosus sp. May 14 1.9 ± 2.4 1.9 ± 2.7
June 56 11.9 ± 6.6 3.6 ± 3.1 ∗∗
July 130 12.5 ± 7.1 23.6 ± 16.1
August 88 6.7 ± 6.3 18.1 ± 14.7 ∗
Guignatus pusillus May 42 5.6 ± 6.3 6.1 ± 3.8
June 83 13.3 ± 9.5 9.7 ± 9.5
July 55 10.0 ± 9.1 5.3 ± 6.1
August 43 1.1 ± 1.3 10.8 ± 15.1
H<strong>al</strong>iplinus heydeni June 20 4.7 ± 5.9 0.8 ± 1.3
July 44 5.6 ± 5.6 6.7 ± 5.0
August 75 2.7 ± 2.7 18.3 ± 19.3 ∗
Laccophilus ssp. May 6 0.6 ± 1.1 1.1 ± 1.3
June 155 29.2 ± 22.3 13.9 ± 10.1
July 281 56.9 ± 31.4 21.1 ± 10.9 ∗∗
August 39 3.1 ± 5.6 7.8 ± 4.9
Noterus sp. May 16 3.1 ± 3.5 1.4 ± 2.8
June 12 2.5 ± 2.5 0.8 ± 1.8
July 128 8.6 ± 7.7 26.9 ± 9.3 ∗∗
August 711 53.5 ± 34.8 144.7 ± 121.8 ∗

75
Table 3. Emergence <strong>of</strong> dragonfly larvae from the P<strong>et</strong>it Badon rice-fields. Given is the tot<strong>al</strong> number
<strong>of</strong> each species emerged from fields with and without pesticide application. In the case <strong>of</strong> the Anax
and Hemianax not <strong>al</strong>l exuviae could be correctly classified to one type <strong>of</strong> fields because <strong>of</strong> an
accident. chi 2 -test: ns not significant, ∗∗∗ P ≤ 0.001, – not an<strong>al</strong>ysed
Species Numbers emerged from fields Tot<strong>al</strong> chi 2 -v<strong>al</strong>ue
With pesticide Without pesticide
Lestes sponsa (Hansemann) 1 0 1 –
Ischnura elegans (Vander L.) 156 153 309 0.03 ns
Ischnura pumilio (Charp.) 4 4 8 –
Erythromma viridulum (Charp.) 2 0 2 –
Anax parthenope (Sélys) 89 –
67 83
Hemianax ephippiger (Burm.) 108 –
Orth<strong>et</strong>rum <strong>al</strong>bistylum (Sélys) 1 1 2 –
Orth<strong>et</strong>rum cancellatum (L.) 7 42 49 25.00 ∗∗∗
Crocothemis erythraea (Brullé) 143 111 254 3.58 ns
Symp<strong>et</strong>rum fonscolombii (Sélys) 151 250 401 24.44 ∗∗∗
fields, abundance data on <strong>al</strong>l taxa were used. It was
found that the diversity (Shannon–Weaver, H s )increased
with time. In May, it was comparatively low:
0.86 with <strong>insecticide</strong> and 1.08 without. In June, it was
1.44 with <strong>insecticide</strong> application and 1.18 without. In
contrast, in July and August the diversity was higher
in the untreated fields (July: H s = 2.11, August: H s =
2,72) than in the treated fields (July: H s = 1.58, August:
H s = 1.82).
Discussion
Our study showed 1. a strong succession in the
macroinvertebrate community <strong>of</strong> experiment<strong>al</strong> ricefields
during the irrigation period and 2. differences in
density <strong>of</strong> a number <strong>of</strong> taxa, as well as differences in
tot<strong>al</strong> density and biomass b<strong>et</strong>ween fields treated with
<strong>insecticide</strong>s and <strong>insecticide</strong> free-fields.
Macroinvertebrate community structure and
succession
Figure 1. Mean tot<strong>al</strong> macroinvertebrate drymass (A) and density
(B) per m 2 (± SE) in the experiment<strong>al</strong> rice-fields <strong>of</strong> P<strong>et</strong>it Badon during
four sample-periods from May to August, 1997 (see ‘M<strong>et</strong>hods’)
and in fields with <strong>insecticide</strong> application and without application
□ (n=36 samples per occasion and type <strong>of</strong> field). Results <strong>of</strong>
2-way-ANOVA are given, addition<strong>al</strong>ly, differences per month are
tested with a posteriori an<strong>al</strong>ysis’: ns = not significant, ∗ = P ≤ 0.05,
∗∗ = P ≤ 0.01, ∗∗∗ = P ≤ 0.001.
The macroinvertebrate community structure <strong>of</strong> temporary
w<strong>et</strong>lands in gener<strong>al</strong> is influenced by the habitat
duration (Williams, 1987, 1997; Schneider & Frost,
1996) and the predictability <strong>of</strong> the dry and w<strong>et</strong> periods
(Williams, 1987). Which species occurs in a given
temporary w<strong>et</strong>land depends on its life history adaptations,
e.g. the adaptation to drought, the duration
<strong>of</strong> development, the timing <strong>of</strong> emergence, the ability
to colonise. As a result, the community structure <strong>of</strong>

76
temporary w<strong>et</strong>lands is characterised by a fast succession
which is typic<strong>al</strong> for a given type <strong>of</strong> habitat (see
Williams, 1987). For rice-fields, these successions are
described, e.g. by Heckman (1974, 1979). The community
and its succession in our rice-fields was similar
in most aspects to that recorded from Greek rice-fields
(Schnapauff, 1995) and to those described by Williams
(1997) for temporary waters in England and the U.S.A.
Schneider & Frost (1996) compared data on the
presence / absence and the abundance <strong>of</strong> species in
different temporary ponds in Wisconsin with three
models <strong>of</strong> community structure incorporating random
forces, life history and biotic interactions. They found
that the model <strong>of</strong> life history adaptations explained
patterns <strong>of</strong> species’ occurrence but not <strong>of</strong> abundance
which best fit a model incorporating factors such
as predation and comp<strong>et</strong>ition. These factors became
particularly important with increasing duration <strong>of</strong> a
habitat. This pattern seems to be reflected in the P<strong>et</strong>it
Badon rice-fields. The earliest colonisers were mostly
oligocha<strong>et</strong>s and chironomids. Both are resistant to
drought (Kenk, 1949; Hinton, 1953; Williams, 1987)
and due to this, they survived to make up the main part
<strong>of</strong> the community in May. In June, oligocha<strong>et</strong>es decreased
while gastropods increased. The latter are <strong>al</strong>so
resistant to drought (e.g. Marazan<strong>of</strong>, 1969) and may
have been able to survive on the dried-up fields, but
their entry from irrigation channels can not be ruled
out. In rice-fields <strong>of</strong> the Ebro-delta, Physella acuta
shows a similar increase from May to July (González-
Solís & Ruiz, 1996). Other early colonisers are aquatic
be<strong>et</strong>les and corixids, which are able to colonise as
adults (Williams, 1987). So, during the first phase
<strong>of</strong> the flooding period groups with efficient surviv<strong>al</strong>
or re-colonisation adaptations, mostly phytophags or
d<strong>et</strong>ritivors, dominate the community, representing >
95% <strong>of</strong> <strong>al</strong>l macroinvertebrates.
As the season progressed, the community’s pr<strong>of</strong>ile
changed: about 15% in July and up to 30% in August
were predators like odonates, some be<strong>et</strong>les and
notonectid bugs. The late appearance <strong>of</strong> the odonates
cannot be an effect <strong>of</strong> mort<strong>al</strong>ity due to drought in
winter: many species are able to survive those periods
as larvae or eggs (e.g. Corb<strong>et</strong>, 1962; Watson, 1981).
Their scarcity during the first months may be due to
ploughing in March or April (see <strong>al</strong>so Aguesse, 1960).
The main sources <strong>of</strong> the rice-field populations <strong>of</strong> these
groups are permanent w<strong>et</strong>lands or natur<strong>al</strong> temporary
w<strong>et</strong>lands. Adults there do not emerge before late April
and most species emerge later (see Dommang<strong>et</strong>, 1987)
and consequently they deposit their eggs in the ricefields
relatively late. In odonates particularly, only
those species having a short duration <strong>of</strong> egg and larv<strong>al</strong>
stage (less than 100 days) are able to emerge successfully
from rice-fields (Aguesse, 1960; Asahina, 1972;
Schnapauff <strong>et</strong> <strong>al</strong>., <strong>2000</strong>). Other species, and <strong>al</strong>l late
ovipositons, cannot survive there is not sufficient time
for to emerge before drainage; in these cases, ricefields
are ecologic<strong>al</strong> traps. Anyway, odonate larvae
<strong>al</strong>one made up 18% <strong>of</strong> the community in August in the
untreated fields. In odonates, as well as in other predators,
interspecific and intraspecific comp<strong>et</strong>ition for
space and food and intraguild predation is usu<strong>al</strong>ly an
important factor (Sih, 1987; Johnson, 1991). Blaustein
(1990) and Blaustein <strong>et</strong> <strong>al</strong>. (1996) describe that invertebrate
communities <strong>of</strong> rice fields and temporary pools
are organised by predators such as flatworms or s<strong>al</strong>amander
larvae. One can easily imagine that late in the
season, predation and comp<strong>et</strong>ition become factors as
important in the invertebrate community <strong>of</strong> rice-fields
as in longer-lasting temporary w<strong>et</strong>land (Schneider &
Frost, 1996).
<strong>Effects</strong> <strong>of</strong> <strong>insecticide</strong> application
Insecticides are applied to rice-fields in order to reduce
the loss <strong>of</strong> crops due to phytophagous insects,
among others, feeding on the rice plant (see Way <strong>et</strong>
<strong>al</strong>., 1991). Concomitantly, so-c<strong>al</strong>led ‘non-targed species’
are <strong>al</strong>so affected. In our study, we found that
in 12 taxa, <strong>al</strong>l <strong>of</strong> them insects, the densities were
significantly lower at least in 1 month in the fields
in which <strong>insecticide</strong>s were used compared to fields
without <strong>insecticide</strong> application. On the other hand, in
11 other taxa, the densities did not differ b<strong>et</strong>ween the
treatments after <strong>insecticide</strong> application, or were even
higher following the <strong>insecticide</strong> <strong>applications</strong>. These
differences in the reaction <strong>of</strong> different species and
groups <strong>of</strong> macroinvertebrates may be caused by sever<strong>al</strong>
factors. The first, and most obvious, is selective
toxicity <strong>of</strong> the <strong>insecticide</strong> to different taxa (e.g. overviews
in Muirhead-Thomson, 1987; Anderson, 1989;
Coats <strong>et</strong> <strong>al</strong>., 1989; Schulz & Liess, 1995). However,
a constant problem in field studies like this one is
that sever<strong>al</strong> other factors may influence the species’
densities. Synergistic effects b<strong>et</strong>ween <strong>insecticide</strong>s and
factors like biotic interactions or farming operations
may <strong>al</strong>so influence the densities <strong>of</strong> selected species
(Takamura, 1985; Simpson <strong>et</strong> <strong>al</strong>., 1994a, b).
In our study, we used three different types <strong>of</strong>
<strong>insecticide</strong>s: lindane (γ -HCH) in combination with
diazinon (an organophosphate) in June, and <strong>al</strong>-

77
pham<strong>et</strong>hine (a synth<strong>et</strong>ic pyr<strong>et</strong>hroid) in August. In July,
1 month after the application <strong>of</strong> lindane and diazinon,
we found significant lower densities <strong>of</strong> nine insect taxa
(group 1, see above) in the treated fields than in untreated
fields. An acute toxicity <strong>of</strong> lindane to many
insects was found at much lower concentrations <strong>of</strong>
lindane than those used in our study (e.g. Maund <strong>et</strong> <strong>al</strong>.,
1992; Schulz & Liess, 1995). Thus, the lower densities
<strong>of</strong> the taxa from group 1 in the treated fields may be
a direct effect <strong>of</strong> mort<strong>al</strong>ity due to these <strong>insecticide</strong>s.
The same may be true for the Culicidae (group 2)
which were <strong>al</strong>so found in lower density in July after
the lindane and diazinon treatment.
On the other hand, a number <strong>of</strong> taxa seemed unaffected
by the application <strong>of</strong> lindane and diazinon.
In some, including Physella acuta and Crocothemis
erythraea, no significant differences in density were
found at <strong>al</strong>l, while in others, e.g. Gyraulus chinensis
and Ischnura elegans, in July even a higher density
was found in the treated fields. These results may
indicate a high tolerance to lindane in these taxa.
Gastropods are known to be relatively tolerant <strong>of</strong> <strong>insecticide</strong>s
including lindane, diazinon and pyr<strong>et</strong>hroids
(Bluzat & Seuge, 1979; Arthur <strong>et</strong> <strong>al</strong>., 1983; Coats <strong>et</strong>
<strong>al</strong>., 1989). This may <strong>al</strong>so be true in other non-insect
taxa like leeches and oligocha<strong>et</strong>es which were <strong>al</strong>so not
affected. In Lymnea stagn<strong>al</strong>is (L.), Bluzat & Seuge
(1979) found an acute toxicity (48h LC 50 ) at a concentration
<strong>of</strong> 7300 µg/l. The LC50 for other non-insect
groups was <strong>al</strong>so high: with Daphnia it was 645 µg/l;
with Rana 8630 µg/l (Thybaud, 1990).
The differences in the reaction to the first <strong>insecticide</strong>
application may <strong>al</strong>so have been influenced by
different life cycles. This may illustrated by the case
<strong>of</strong> libellulid dragonflies. Crocothemis divisa and C.
sanguinolenta studied by Muirhead-Thomson (1973)
were highly susceptible to the organophosphorous <strong>insecticide</strong>
fenthion. The mort<strong>al</strong>ity after 24 h <strong>of</strong> exposure
at 0.01 ppm fenthion was 70%; after 48 h at 0.005
ppm it was 83%. In our study, the closely related C.
erythraea was not affected in the <strong>insecticide</strong> treatment.
Schnapauff <strong>et</strong> <strong>al</strong>. (<strong>2000</strong>) found a similar result with
the organophosphate parathion in Greek rice-fields. In
contrast, in the libellulid S. fonscolombii we found
significantly lower densities and emergence in fields
with application <strong>of</strong> lindane and diazinon. The explanation
could be found in the timing <strong>of</strong> colonisation
<strong>of</strong> the rice-fields. Whereas adults <strong>of</strong> S. fonscolombii
were observed long before the <strong>insecticide</strong> application,
adults <strong>of</strong> C. erythraea in our as well as in the Greek
rice-fields were not registered until the application <strong>of</strong>
the <strong>insecticide</strong>s (Katzur & Lepkojus, pers. observ.,
Ullmann, 1995). Thus, oviposition <strong>of</strong> S. fonscolombii
started before the <strong>insecticide</strong>s were applied and
the larvae were contaminated by the <strong>insecticide</strong>s. In
C. erythraea, oviposition started more than 2 weeks
after the application and the larvae were probably
not contaminated with lindane, which has a relatively
short period in which it is effective and even with
diazinon (or parathion) in which effects in pure water
were found 2 weeks after application (Perkow, 1988).
Moreover, in the presence <strong>of</strong> suspended rice-field sediment,
to which lindane is adsorbed to a high extend
after 1 day (see Thybaud, 1990), the concentration
may have been much lower than c<strong>al</strong>culated for pure
water. Other taxa, too, avoided or had only minor contact
with lindane and diazinon, e.g. Sigara later<strong>al</strong>is
and Corixa punctata which, had their peak before
the first application and, after it, were found in low
numbers in both treatments.
In the damselfly Ischnura elegans, the situation
seems to be more complex. In July, it occurred in
higher densities in the fields treated with <strong>insecticide</strong>s,
but in August it was the opposite. It was obviously not
affected by the application <strong>of</strong> lindane and diazinon.
Absence <strong>of</strong> effect <strong>of</strong> diazinon in the field was <strong>al</strong>so
described for a North American species <strong>of</strong> Ischnura
(Arthur <strong>et</strong> <strong>al</strong>., 1983). The higher density <strong>of</strong> I. elegans
may have been a result <strong>of</strong> the reduction <strong>of</strong>
potenti<strong>al</strong> predators and / or comp<strong>et</strong>itors due to the <strong>insecticide</strong>s,
including carnivorous bugs (e.g. Notonecta,
see Thompson, 1987) and other odonate larvae. However,
after the application <strong>of</strong> <strong>al</strong>pham<strong>et</strong>hine, the density
<strong>of</strong> I. elegans was reduced. This may have been a direct
effect <strong>of</strong> the pyr<strong>et</strong>hroid. Am<strong>al</strong>raj (1996) found that <strong>al</strong>pham<strong>et</strong>hine
has acute toxic effects on a predatory culicid
at concentrations below 5 µg/l. As a result <strong>of</strong> the
different sensitivity to the different <strong>insecticide</strong>s, the
number <strong>of</strong> emerged individu<strong>al</strong>s did not differ b<strong>et</strong>ween
the treatments (Table 3). According to our results, I.
elegans seems to be the only species which was affected
by the second <strong>insecticide</strong> application, <strong>al</strong>though,
it is possible that the effects <strong>of</strong> the pyr<strong>et</strong>hroid on other
taxa were not d<strong>et</strong>ectable because these were <strong>al</strong>ready
affected by lindane and / or diazinon. In many <strong>of</strong> these
species, no recovery was found even 2 months after
the first application and this may be an effect <strong>of</strong> the
<strong>al</strong>pham<strong>et</strong>hine application at the beginning <strong>of</strong> August.
The tot<strong>al</strong> macroinvertebrate biomass <strong>al</strong>so seemed
to be affected by the <strong>insecticide</strong> application. In the
treated fields, the biomass peaked in July, while in
the untreated fields the peak was in August. The rapid

78
increase in the former b<strong>et</strong>ween June and July resulted
mainly from an enormous increase in gastropod density
which made up 75% <strong>of</strong> the whole community in
the fields treated with lindane in July. As described
above, the gastropods were not negatively affected by
the <strong>insecticide</strong> <strong>applications</strong>. However, this tolerance
does not explain why G. chinensis had a higher density
in the fields treated with lindane. The reason for
this may be an indirect effect <strong>of</strong> the <strong>insecticide</strong> application
similar to that described for I. elegans: the
density <strong>of</strong> many predatory species feeding option<strong>al</strong>ly
(e.g. odonates, Blois, 1985) or mainly (e.g. Berosus,
see Klausnitzer, 1996) on snails was reduced due to
the application <strong>of</strong> lindane (see above) and the increase
<strong>of</strong> gastropods in the treated fields may have led to a
decrease <strong>of</strong> predators. Comparable results were found
in Japanese rice-fields: chironomid and ostracod densities
increased in rice-fields treated with pesticides
because <strong>of</strong> a decrease in aquatic be<strong>et</strong>le and dragonfly
density (Takamura & Yasuno, 1985).
The <strong>insecticide</strong> application clearly influenced the
usu<strong>al</strong> succession <strong>of</strong> rice-fields which is described
above. Because <strong>of</strong> increased mort<strong>al</strong>ity in a number
<strong>of</strong> taxa, typic<strong>al</strong> biotic interactions which influence
the community later in the season (see above) were
reduced in treated fields and the increased densities
were mainly <strong>of</strong> gastropods, which pr<strong>of</strong>ited from the
decrease in predators. As a result, species diversity
was lower in fields with <strong>insecticide</strong> application than in
those without. This decrease in diversity may not only
have implications for environment<strong>al</strong> protection. An increased
diversity <strong>of</strong> predators may <strong>al</strong>so help to control
natur<strong>al</strong> pests (Risch <strong>et</strong> <strong>al</strong>., 1983; Way & Heong, 1994;
S<strong>et</strong>tle <strong>et</strong> <strong>al</strong>., 1996). Consequently, the over<strong>al</strong>l effect
<strong>of</strong> <strong>insecticide</strong>s on reduction <strong>of</strong> pest damage should
be studied carefully in light <strong>of</strong> the effects on species
diversity.
Acknowledgements
We wish to thank Jens Rolff for some gener<strong>al</strong> comments,
R<strong>al</strong>f Schulz for comments on ecotoxicologic<strong>al</strong>
aspects and Nicolas Beck for help in the fields. Diana
Wilker kindly corrected the paper. We <strong>al</strong>so thank Inga
Schnapauff and Kerstin Ullmann <strong>al</strong>lowing us to use
data from their unpublished thesis.
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