Margins of agricultural fields as habitats for pollinating insects

Agriculture, Ecosystems and Environment, 40 (1992) 117-124

117

Elsevier Science Publishers B.V., Amsterdam

Margins of agricultural fields as habitats for pollinating insects Jan Lagerl/ff a, Josef Stark b and Birgitta Svensson ~ aDepartment of Ecology and Environmental Research, P.O. Box 7072, Swedish Universityof Agricultural Sciences, S- 750 07 Uppsala, Sweden bDepartment of Animal Nutrmon and Management, P.O. Box 7024, Swedish Universttyof Agricultural Sciences, S- 750 07 Uppsala, Sweden

ABSTRACT Lagerliff, J., Stark, J. and Svensson, B., 1992. Margins of agricultural fields as habitats for pollinating insects. Agric. Ecosystems Environ., 40: ! 17-124. The occurrence of pollinating insects in field margins with different vegetatmn was studied in field experiments. Some margins were widened and vegetation was established by sowing of leguminous plants or was allowed to invade spontaneously. The communities of pollinating insects in reclaimed field margins were compared with those of a margin with a naturally diverse flora and an adjacent pasture. A beehive was placed m the area and the collection of pollen by the honey-bees was followed over the season in order to compare the bees' preferences with the supply of flowering plants available in the different experimental field margins. The sown leguminous plants were very attractive to most insect groups, especially bees and bumble-bees, and their pollen constituted an important part of the bees' total catch. The vegetation established by spontaneous succession especially attracted SyrDhidae and other groups of Diptera. Butterflies were found in all vegetation types. It is concluded that small areas with flowering plants can give highly positive effects. The key question is how to avoid weed problems and keep the most attractive plant species with a minimum ofcost and effort.

INTRODUCTION

One possibility to ameliorate the situation for pollinating insects in the modern agricultural landscape is to enlarge remaining field margins, protect them from agrochemicals, and create new zones with permanent vegetation in a network over the landscape (Missonier and Ryszkowski, 1986; Marshall, 1988; Welling, 1988). The influence of such measures on pollinating insects is studied in field experiments, as one part of a project concerning protection of invertebrate fauna (Lagefliff and Wallin, 1988 ). This paper presents some initial results from investigations of the pollinatCorrespondence to: Jan Lagerl6f, Department of Ecology and Environmental Research, P.O. Box 7072, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden.

118

z.LAGERLOFETAL.

ing insects in a selection of vegetation types in the studied field margins. Abundance of flower-visiting insects in field margins and nearby pasture with ":turally occurring vegetation was compared with field margin areas sown :ith leguminous plants. In addition, the importance of the studied field margins for the foraging of honey-bees was investigated by analysis of pollen gathered by a bee community. This was related to the occurrence of the different plant species in the margins. MATERIALSAND METHODS The experimental site is situated about 10 km southeast of Uppsala in central Sweden in a plain area intensively used for agriculture. Areas of separate fields are mostly larger than 25 ha. Pipe drainage systems are installed and open ditches and other non-cultivated areas are scarce. The main crops in the area are winter wheat, barley and rape. Grass and clover leys are also common but were not grown near the experimental plots during 1989. Cereal crops are regularly treated wi~h herbicides of fenoxy acid type, which are more and more replaced by Glin. ! asecticides (e.g. Metasystox R 100 or Pirimor) are used in cereals against aphids, and fungicides (e.g. Tilt) are often used. In rape insecticides of pyrethroid type are regularly used, while herbicides are only rarely usee Experimental plots measured 2 m × I O m. They were repeated in four replicates randomly distributed along field margins or in nearby pasture. Examined treatments were: ( 1 ) Melilot, field margin sown with a mixture of leguminous plants, white melilot (Melilota alba) in dominance; (2) Red clover, field margin sown with clover and ley grasses, red clover ( Trifolium pratense) in dominance; (3) Weed, field margin with a diverse flora of weeds; (4) Ditch bank, naturally diverse flora of herbs and grasses on a field margin along a ditch; (5) Dry hill, natural soecies-rich dry pasture. All flower-visitinginsects present in the plots were counted about three times per week, both morning and evening, during summer 1989. The observer walked slowly along the field margin, about 1O m m i n - ' , counting all the insects on flowers (Pollard et al., 1975; Banaszak, 1980). Flowering plant species in the plots were also recorded. The insects were divided into species or higher taxa and were classified into five groups: ( 1 ) Honey-bees (Apis mellifera); (2) Bumble-bees (Bombus spp.); (3) Butterflies and moths (Lepidoptera); (4) Hover-flies (Syrphidae); (5) Other insects (mostly Diptera). A beehive was placed ir~ tb~- area a~_~ :he collection of pollen by the bees was monitored using a pollen trap, in order to compare the bees' preferences with the supply of flowering plants available in the experimental plots. ANOVA and LSD was used to test the significance of differences observed in abundance of the five groups of pollinating insects. Since the experiments were made in semi-natural vegetation types, the experimental plots of each

AGRICULTUR/~ L FII"LD MARGIN HABITATS FOR POLLINATING INSECTS

1 19

vegetation type were not interlaced with plots in other vegetation types. However, to be able to perform ANOVA it was assumed that all plots were randomised. We coix,sider the possible errors introduced by this to be small, since all experiments i:avestigated are situated near each other in a homogeneous area dominated b~,,intensive agriculture. RESULTS

Twenty-six taxa of pollinating insects were distinguished in the five experimental treatments c~uring the investigation period (Table I ). In addition, blossom beetles (Mel~getes spp. ) were found, but their numbers could not be estimated by the metli~od used due to their small size and sometimes large numbers. A somewhat higher species number of butterflies was foupd at the dry hill pasture site than at the other sites (Table 1 ). However, the number of individuals was lower on the dry hill than at the other sites (Fig. I c), mostly due to absence or low numbers of the otherwise most common species, i.e. Pieris brassicae and Aglais urticae. Melilot was the most attractive among the investigated vegetation types to honey-bees and flies other than Syrphidae (Table 1, Fig. 1 ), while bumblebees were most abundant in red clover. Syrphidae showed no significant differences between treatments. Unfortunately data are lacking for melilot at 2 August, when the highest numbers of Syrphidae during the summer were found in the ditch bank with naturally diverse flora and in the weed-dominated treatment. The bees' daily harvest of pollen depends on the number of bees, the amount of pollen available, and the weather. The highest catches of pollen lumps were recorded in the period 15 July-15 August (Fig. 2), with a decline during the first days of August, probably due to rainy weather. Dominating pollen sources (Fig. 3) were the cultivat~'l plants rape and turnip rape (Brassica napus and Brassica rapa ), while melilot t Melilota alba), and red clover ( Trifolium pratense). Pollen lumps from some wild plants were also found in fairly high quantities; hoary plantains (Plantago media), meadow sweet (Filipendula ulmaria), and burdock (Arctium tomentosum). Small quantities of pollen from Taraxacum gr. vulgate, Tilia cordata, Matricuria maritima, Hypericum sp., Centaurea jacea, and Epilobium angustifolium were also found. The seasonal variation in preference for different pollen sources as presented in Fig. 3 shows rather good similarity with the flowering season of these species in the experimental plots (Fig. 4). One exception is red clover. It was harvested on 27 July in the experimental plots, but the bees obviously gathered red clover pollen from other unharvested areas, and it became a dominant pollen source during the later part of the summer.

! 20

~. LAGERLOFET AL.

TABLE 1 Taxa of flower-visiting insects in four vegetation types in field margins and in one adjacent dry pasture site, Percentile distribution in the difle~'c~t treatments and total numbers recorded during the investigatloa period June-August 1989. For description of treatments see Material and Methods Insects

Percent oftotal number Melilot

Red clover

Total number Ditch bank

Weed

1.3 10

0.3 0

Dry hill

Apoidea

Apis mellifera Apoidea, solitary

Bombus terrestr:s/lucorum Bombus lapidarlus Bombus agrorum

98 20

0.0 40

0.4 30

2422 I0

23

71

5

I

19

73

7

2

0 0 0

97 275 41

29

71

0

0

32

31

13

2I

0 0

0 0

0 0

0 0

81

26 0 0 0 0 6 0 26

3 100 100 0 66 0 100 6 15 50 0

10 80 3 2 2 14 30 2 17

17 0 100 0 19 45 0 0

52 0 0 0 6 21 0 5

0 33 0 0 69 13 50 69

18 69 0 0 1 48 0 0 0 0

10 i0 14 0 2 4 0 100 0 0

31 8 86 100 39 30 0 0 0 0

39 9 0 0 45 !8 89 0 100 0

2 4 0 0 13 0 I1 0 0 100

772 984 7 3 87 24 9 1 I I

Lepidoptera

Pterts brasslcae Pwris nap: Anthocaris cardammes Aglais urticae Lycaena spp. Argynnis spp, Mehtaea spp, Heo~es spp. Aphantopus hyperantus Purgus malvae Erynnis rages Others Syrphida¢ spp. Diptera, others Aphidoidea Cieadoidea Heteroptera Thysanoptera Formieidae Cerambycidae Cantharidae Symphyta Total

I

4979

DISCUSSION

The investigation method for counting insects seems to be efficient for larger species, such as bees and butterflies, but is less meaningful for observation of smaller or very numerous insects. For investigation of such small species, suction traps shuld be used (LagerlSf and Wallin, 1992). One should also keep in mind that there is a considerable activity with other species involved, dur-

A G R I C U L T U R A L FIELD M A R G I N HABITATS FOR P O L L I N A T I N G INSECTS

Honey-bees %

A

Ap/s melldera

30[ :~s|

Slgmftcanf differences

;~°/

P<0001

121

Bumble-bees

~A= 2422

%

B

Bombussp

~_

=413

//~

melllof > ofhers

/

/-

J

i a

tO

5 15/6

30/6

7/7

24/7

8/8

25/8

b

fl

•

16/6

30/6

6'7

20/7

25/8

I "- ~'o:"o' ,..edo,ove,:_,:~,,chb~_.~ Hover-flies

Butterflies %

C

L~pidoptera

14

.

Syrphldae

~ = 772

30¸

= 242

a 20'

10

'i

:,b

4i

15/6 516

10

'\

301~

fJ

3/7

-~'- Melllot _,+,. Wried

~

5]

17/7

26/7

25/8

-. 15/6

26/6

I N- MeJllOl

Red clover -P- Ditch bank

"It" Dq/hill

3/7

-U

29/7

- ~ Red clover--m-- Ditchbank ~

2/8 Weed

25/8 ]

J

Other insects mostly flies

%

~=

1126

25' 20' a

a

15. 10. 5 0"

15/6

26/6

3/7

1~7

24/7

8/8

25/8

Fig. 1. Distribution of insect groups in five vegetation types, 19 June-22 August 1989. Abundance of insects in each vegetation type expressed as percent of total number of the insect group in all vegetation types examined during the whole investigation period. Values with different letters are significantly different ( P < 0.05). (Data lacking for melilot 2 August. Red clover plots harvested 27 July. )

122

3. LAGERL6F ET AL.

'ooo I 3500" ~ 3O00" O =1.

"~ 2500

8

2o00.

6 .~ 1500' E

i

i000

500" 30/6

7/7

20/7

2/8

21/8

Fig. 2. Pollen from a beehive in the experimental area. Sampling period 30 June-? 1 August 1989. Total number of pollen lumps collected by the bees at each sampling date.

~

90.

.

.

.

.

.

.

.

.

.

80. . . . . . . . . . . . . . . . . .

~. 70'0

40]

~ 5O-

_

20"

•

15/6

[

~

30/6

17/7

8/8

25/1

Hoary plantain -"9-- Rape a. Red clover White rnehlot ~ Meadow sweet --=- Burdock

Fig, 3. Pollen from a beehive in the experimental area. Sampling period 30 June-21 August 1989. Relative proportion of pollen from the dominating pollen sources. (Small quantities of pollen from Tara.~acumgr. vulgare, Tilia cordata, Matrtcaria maritima, Hypericum sp., Centaureajacea, and Epilobium angustifolium were also found. )

ing the night-time. This activity can hardly be recorded by this method, except during the light Nordic summer nights. Owing to very dry and warm weather in spring and early summer most of the flowering period at the dry hill pasture site had passed when the investigation started in late June. Therefore, the importance of this beautiful site with such

AGRICULTURAL

FIELD

MARGIN

HABITATS

FOR POLLINATING

INSECTS

123

Flower-season in the experimental plots . . . . . . . . . . .

..........

N

M

t

:

~

;

=

=

,g

_.~

,g ..............................

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CI

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. . . . . . . . . . . . . . . .

1916

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--M- Hoary plantain

I

N

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'

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

26/7

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El

[]. . . . . . . . .

22/8

.--A- Red clover

- - x - Meadow sweet --=- Burdock

Fig. 4. Flowering season in the the honey-bees.

experimentalplots of the plants that provided the most pollen to

a diversity of flowering plants has not been fully elucidated in this investigation. Our results mostly confirm earlier findings concerning the preference of different insect groups for different vegetation types. Melilot is known to be attractive to honey-bees, and bumble-bees are known as major pollinators of red clover (Schwan and Martinovs, 1954). Plants of the family Apiaceae, which are common in ditch, and Asteraceae, which are represented both in the ditch and the weed treatments, are important for the occurrence of Syrphidae as was reported by Molthan and Ruppert ( 1988 ). The strong attraction of melilot for honey-bees found in this investigation is remarkable. Although melilot was grown only in one field margin, altogether 80 m 2, and nowhere else in the area, and the beehive was situated almost l km away it dominated the pollen catch of the bees during several weeks (Fig. 3). In order to keep the favoured plant species in the field margins it is essential to protect the field margins from herbicides. Otherwise a few resistant grass and herb species take over, such as Elymus repens, and very few pollinating insects will be found (Lagerlff and Wallin, 1992 ). It is therefore desirable to widen the field margins to at least 2 m and to keep a spray-free zone in the adjacent field. CONCLUSION

Honey-bees and bumble bees are especially favoured by certain cultivated plants, while a diversity of wild plant species along field margins is favourable

124

] LAGERLOFETAL.

for other groups of pollinators. These other groups include natural enemies of pest insects and several species reduced by modern agriculture. Small areas with flowering plants between arable fields show positive effects for pollinating insects. The key question is how to avoid weed problems, and how to keep the most attractive plant species with a minimum of cost and effort. ACKNOWLEDGEMENT

This project is financially supported by the foundation 'Stiftelsen Oscar och Lili Lamms minne'.

REFERENCES Banaszak, J., 1980. Studies on methods of censoring the numbers of bees ( Hymenoptera, Apeidea). Pol. Ecol. Stud., 6: 355-366. LagerlOf, J. and Wallin, H., 1988. Cropping systems, field margins and invertebrate fauna in Swedish agriculture. INTECOL Bull. (Ecol. Int. ), 16: 55-59. LagerlOf, J. and Wallin, H., 1992. The effect of vegetation composition of field margins on the occurrence of beneficial arthropods. Agric. Ecosystems Environ., submitted. Marshall, E.J.P., 1988. The ecology and management of field margin floras in England. Outlook Agric., 17 (4): 178-182. Missonier, J. and Ryszkowski, L. (Editors), 1986. Impact of structure of agricultural landscape on crop protection. Colloq. I'INRA, 36. INRA, Paris, 19O pp. Molthan, J. and Ruppert, V., 1988. Zur Bedeutung bliihender Wiltkr[iuter in Feltranden und ~,ckern f'tir bliitenbcsuchende Nutzinsekten. In: M. Welling (Editor), Auswirkungen yon Ackerschonstreifen. Beitr~ige vom Symposium: Ackerschonstreifen -- positive Ausw~rkungen f'tir die Landwirtschaft? Mitt. Biol. Bundesanst. Land- Forstwirtsch., Berlin-Dahlem, Heft, 247: 85-99. Pollard, N., Elias, D.O., Skelton, M.J. and Thomas, J.A., 1975. A method of assessing the abundance of butterflies in Monks Wood National Reserve in 1973. Entomol. Gaz., 26: 79-88. Schwan, B. and Martinovs, A., 1954. Studier Over binas (Apis mellifica) pollcndrag i Uituna. Summary in English: Studies on the collection of pollen by honey-bees (Apis mellifica) at UItuna (Sweden). Kungl. lantbruksh0gskolan och statens lantbruksfOrsOk,Statens husdjursfOrsOk, Meddelande nr. 57, Norrtiilje, 35 pp. Welling, M., 1988. Auswirkungen yon Ackerschonstreifen. Beitr~ige veto Symposium: Ackerschonstreifen-- positive Auswirkungen f'tirdie Landwirtschaft? Mitt. Biol. Bundesanst. LandForstwirtsch., Berlin-Dahlem, Heft, 247, 165 pp.