102 E. Huusela-Veistola, A. Vasarainen Agriculture, Ecosystems and Environment 80 2000 101–112
perennial strips, have become more and more popu- lar Nentwig, 1989; Thomas et al., 1992. The main
purpose of the strips is to increase the numbers of natural enemies and their potential for natural control.
Furthermore, the biodiversity of agroecosystem in- cluding the insect diversity is enhanced by increasing
the species richness and structural diversity of plants Murdoch et al., 1972; Lawton, 1983. A diversified
plant community offers more microhabitats and fac- ultative host species for herbivores and increases the
abundance of alternative prey species for polyphagous predators Andersson, 1990. Therefore it is supposed
that strips can increase the biodiversity of fields. An- other important function of perennial strips is to act as
a buffer zone for decreasing erosion and leaching of nutrients.
Compared with cultivated fields, which are ecosys- tems maintained by human activity at an early
stage of succession Ryszkowski, 1979, perennial strips and other man-made semi-natural habitats may
change during succession. A change in the species composition and structure of vegetation changes the
environment of insects e.g. microclimates, food sup- plies and hiding places. Therefore long-term studies
concerning insect fauna and succession of strips are required.
Because it is not feasible to determine the biodi- versity of the wider insect fauna in the agroecosys-
tem, the study concentrated on leafhoppers Hom., Auchenorrhyncha. The effects of perennial strips
on polyphagous predators are presented elsewhere Huusela-Veistola, 1998. Auchenorrhyncha is one
of the best known taxa in the fields in Finland, and over 60 species occur in cereals Raatikainen, 1971,
1972; Raatikainen and Vasarainen, 1971, 1973, 1976. Leafhoppers are an important insect group in the
field ecosystem and are herbivorous sap-feeding and day-active insects. Most species in cereal fields
are oligophagous and their main host plants are gramineous species. They damage plants directly by
feeding or indirectly as vectors of a variety of plant pathogens, e.g. oat sterile dwarf virus Raatikainen,
1970. Natural enemies include insect predators and parasitoids Waloff, 1980, but leafhoppers are also
food for many other animals, e.g. birds and shrews in the agroecosystem. Therefore, a diverse leafhopper
fauna may support a greater general diversity of the agroecosystem.
The aims of the study were 1. to describe the plant succession of perennial strips
in northern conditions where short growing sea- sons and snowy winters are typical;
2. to clarify the difference in insect fauna between cereal and grass strips e.g. do strips increase
leafhopper diversity in the field ecosystem?; 3. to determine the effect of succession on leafhop-
pers in perennial strips e.g. do strips have only a short-term effect on leafhopper diversity?; and
4. to compare the leafhopper fauna of perennial strips with that of other uncultivated biotopes.
2. Materials and methods
2.1. Experimental design The effects of perennial grass strips on the insect
fauna in the cereal ecosystem were studied within the Nummela project in 1992–1995 at the Institute of
Plant Protection, Agricultural Research Centre of Fin- land Huusela-Veistola, 1998. In a large-scale field
experiment, the effects of two pesticide regimes con- ventional and reduced and two cultivation systems
customary, integrated system of cereal production on insect fauna were studied Huusela-Veistola and
Kurppa, 1996; Huusela-Veistola, 1996, 1998. Addi- tional elements constituted the perennial grass strips,
the purpose of which was to increase habitat diversity.
The experimental field was situated on the Num- mela Experimental Farm of MTT in Jokioinen
60
◦
52
′
N, 23
◦
25
′
E about 120 km north-west of Helsinki. Before the field experiment, fields were un-
der conventional grain and grass production and cattle pasture. The perennial grass strips 12 m wide, 420 m
long were situated in the middle of cereal fields 15 ha. In practice, three individual strips were sown
in 1991 with a ‘green fallow seed mixture’ which consisted of timothy Phleum pratense L., meadow
fescue Festuca pratensis Hudson, red clover Tri- folium pratense L. and white clover T. repens L..
The perennial strips were not mown or renewed af- ter the establishment. A 4 m wide strip of Phacelia
tanacetifolia Bentham was added beside the shelter belts in 1992. Sowing of the Phacelia strip was re-
peated annually. In 1992 and 1993 barley cv. ‘Arra’ and in 1994 spring wheat cv. ‘Satu’ were grown in
E. Huusela-Veistola, A. Vasarainen Agriculture, Ecosystems and Environment 80 2000 101–112 103
the surrounding fields. The layout of the experiment is described in Huusela-Veistola 1998.
In 1991, the leafhopper fauna from adjacent biotopes was monitored covering eight seven in oats
sampling dates from 18 June to 7 August 1991. Sam- ples were taken from cultivated fields oats, oats and
grass, winter wheat, grassland as well as from un- cultivated biotopes abandoned field, headland, ditch
bank, edge of forest in Jokioinen near the strip study sites.
2.2. Botanical composition of grass strips Each strip was divided into two blocks accord-
ing to the field plot experiment when samples were taken and analysed. In July each year eight sam-
ple squares 1 m
2
per block were analysed from the perennial grass strips. Percentages of total plant
cover and species composition were estimated visu- ally altogether from 16 samples per individual strip.
Furthermore, plant species found outside the sample squares were listed.
2.3. Monitoring of arthropods Leafhoppers in the grass strips and the fields were
collected with sweep nets. The diameter of the net was 30 cm and one sweep net sample consisted of
60 sweeps. Four sweep net samples per block were taken from the grass strips and from cereal fields. In
1992, only one sample per block was taken from the grass strips. In 1995, only perennial strips from four
blocks were swept. The distance between cereal and grass samples was 50 m. Table 1 gives details of the
sampling programme.
After capture, the samples were frozen for a day and the leafhoppers were removed to 70 alcohol for stor-
age. Leafhoppers were identified to species and poly- morphic species to morphs. Because juveniles could
not be identified reliably, the analysis was limited to adult catches only. Macrosteles sp. females could not
be determined by species and they were allocated to ‘separate species’ in the analysis. Generally they could
be divided into species in the same ratios as their males Raatikainen and Vasarainen, 1971, but this could
not be done as there were no males in the sample. The nomenclature of Auchenorrhyncha complied with
Ossiannilsson 1983.
Table 1 Leafhopper sampling programme and effective temperature
sum+5
◦
C day degrees in 1992–1995
a
Sampling Date
Effective temperature sum dd 1992
1 11 June
327 2
24 June 453
3 26 June
474 4
06 July 566
5 15 July
674 6
23 July 770
7 13 August
1005 1993
1 30 June
499 2
09 July 575
3 20 July
713 4
30 July 815
1994 1
29 June 332
2 14 July
530 3
25 July 676
4 12 August
937 1995
1 16 June
356 2
30 June 503
3 14 July
623 4
27 July 763
a
In 1995, samples taken only from grass strips.
2.4. Statistical analyses In the plant data, dependent variables were total
plant cover, cover of individual plant species, species richness, diversity Shannon H
′
= − 6p
i
ln p
i
where p
i
is the proportion of ith species in the pooled data and evenness Hill E
′
= 6p
2 i
− 1
expH
′
. Total catch of leafhoppers, species richness, abundance of indi-
vidual species, diversity Shannon H
′
and evenness Hill E
′
were dependent variables in the leafhop- per data. For statistical analysis the data was log- or
arcsinsquare root-transformed as necessary to sat- isfy the conditions of normality and homogeneity of
variances.
Effective temperature sum +5
◦
C of the growing season in southern Finland is approximately 1300 dd
day degrees. The leafhopper data was divided into two periods: early summer 0–650 dd and later sum-
mer 650–1300 dd. Means by block period and year were used in analyses except for species richness when
total species richness by block was used. The anal- yses were performed by the MIXED procedure of
the SASSTAT Software Littell et al., 1996. In the
104 E. Huusela-Veistola, A. Vasarainen Agriculture, Ecosystems and Environment 80 2000 101–112
Fig. 1. Number of plant species mean±S.D. in perennial strips in 1992–1995. Years with different letters differed significantly,
p0.05 Tukey’s test.
model, year and period were fixed factors and strip and blockstrip and their interactions were random
factors. Satterthwaite’s approximation was used in de- grees of freedom if one of the covariance parameter
estimates was zero. If the main effects were statisti- cally significant in ANOVA, Tukey’s HSD test was
used to determine significances between levels.
Patterns in whole assemblages were investigated through CANOCO Ter Braak, 1987 by applying de-
trended correspondence analysis DCA to plant and leafhopper data. DCA is a divisive ordination tech-
nique which is based on reciprocal averaging Hill and Gauch, 1980. Before the analysis, the data was
pooled by blocks.
Similarities of leafhopper communities between dif- ferent habitats were studied using index of percentage
similarity by Renkonen 1938 PS=6minp
ij
, p
ik
where p
ij
is the proportion of species i in sample j.
Table 2 Percentages of plant cover and diversity in grass strips mean±standard deviation
a
Mean±S.D. 1992
1993 1994
1995 df
F P
Phleum pratense 7.6±4.5 a
16.5±3.2 a 34.3±4.8 b
34.6±7.4 b 3, 8
30.52 0.0001
Festuca pratensis 12.0±3.4
18.1±5.5 22.8±9.1
15.0±5.6 3, 6.46
3.51 0.0834
Trifolium repens 13.4±5.7 a
11.7±6.1 a 0±0 b
0.3±0.5 b 3, 6
43.98 0.0002
Trifolium pratense 36.5±18.4 a
29.9±7.1 ab 6.0±9.1 bc
0.3±0.5 c 3, 7.39
9.70 0.0060
Total plant cover 78.2±12.1 a
78.0±7.3 a 65.2±8.5 b
57.0±13.4 b 3, 15
15.61 0.0001
Shannon’s H
′
1.47±0.27 a 1.41±0.10 ab
0.98±0.14 ab 0.92±0.24 b
3, 8 6.3
0.0168 Hill’s E
′
0.76±0.11 0.88±0.03
0.88±0.04 0.86±0.05
3, 6 2.6
0.1478
a
Variation between years was tested by ANOVA, differences between pairs of years was tested by Tukey’s test means with the same letter are not significantly different. Satterthwaite’s approximation used in degrees of freedom.
3. Results
