Organic versus conventional management in an apple ... - CiteSeerX

Agricultural and Forest Entomology (2008), DOI: 10.1111/j.1461-9563.2008.00403.x

Organic versus conventional management in an apple orchard: effects of fertilization and tree-row management on ground-dwelling predaceous arthropods M. Miñarro, X. Espadaler*, V. X. Melero† and V. Suárez-Álvarez‡ Servicio Regional de Investigación y Desarrollo Agroalimentario (SERIDA), Apdo. 13, E-33300, La Villa, Asturies, Spain, *CREAF-Unitat d’Ecología, Universitat Autónoma de Barcelona, E-08193, Bellaterra, Spain, †Departamento Biología de Organismos y Sistemas, Universidá d’Uviéu, E-33071, Uviéu, Asturies, Spain and ‡Departamento Biodiversidad y Gestión Ambiental, Universidad de León, E.S.T.I.A, Campus de Ponferrada, Avda, Astorga, s/n, E-24400, León, Spain

Abstract

1 Organic and conventional management of apple orchards may have a different effect on arthropod communities. 2 We conducted a 3-year study to assess the effect of two strategies of fertilizer treatment (organic versus chemical) and three tree-row management systems (straw mulching, tillage and herbicide) on activity-density and biodiversity of epigeic predators. Ground beetles (Carabidae), rove beetles (Staphylinidae), ants (Formicidae) and spiders (Araneae) were sampled monthly with pitfall traps in the same apple orchard during 2003, 2004 and 2005. 3 A total of 4978 individuals were collected. Carabids (56.8% of the total catches) were the most abundant taxonomic group, followed by spiders (20.7%), ants (14.8%) and rove beetles (7.7%). Tree-row management had a greater influence on predator catches than fertilizer treatment. Total predator catches were lower under the mulch. Mulching also reduced carabid abundance, but increased staphylinid catches. 4 Tree row management also had a significant effect on biodiversity parameters. Species richness did not significantly differ among treatments for ants, spiders or the total catches, but was higher on herbicide-treated plots for carabids and on mulched plots for staphylinids. Shannon–Wiener’s diversity index was significantly greater in the mulched and herbicide treated plots for total predators and carabids. For staphylinids, this index was significantly greater on the mulched plots. Fertilizer application strategy only influenced the species richness of rove beetles, which was greater in the chemically-treated plots. 5 The results showed that a change from conventional to organic fertilizer treatment of apple trees may be performed without differential effects on predator activitydensity or biodiversity. However, a change from herbicide treatment to mulching or mechanical weed control may be significant, depending on the taxonomic group. Keywords Araneae , biodiversity , Carabidae , conservation , Formicidae , Staphylinidae.

Introduction Agricultural intensification has led to a significant reduction of biodiversity ( Reidsma et al. , 2006; Hendrickx et al. , 2007). At the farm scale, the management system has usuCorrespondence: M. Miñarro Prado. Tel: +34 985 890 066; fax: +34 985 891 854; e-mail: [email protected] © 2008 The Authors Journal compilation © 2008 The Royal Entomological Society

ally been demonstrated to have a strong influence on the abundance and the diversity of arthropod communities (Hummel et al., 2002; Melnychuk et al., 2003; Clough et al., 2007 ). In apple orchards, the production system has an impact on ground-dwelling arthropods: when orchards with different insecticide regimes are compared, biodiversity and activity-density of ground-dwelling predaceous arthropods are generally lower in orchards managed with broad-spectrum

2

M. Miñarro et al.

Table 1 Treatments in the experimental orchard Fertilizer

Groundcover management

Date

Organic

Chemical

Mulching

Tillage

Herbicide

21 March 2003

750 kg/ha mineral 0 : 12 : 18

—

—

—

26 March 2003 (at planting) 30 May 2003

1 kg/tree worm compost (1.5 :1.4;1) —

200 kg/ha 0 : 18 : 0 270 kg/ha 0 : 0 : 50 —

—

—

—

—

Application

Rotovator

18 June 2003

50 g/tree organic 6 : 8 : 15 400 g/tree worm compost — — 50 g/tree organic 6 : 8 : 15 1000 g/tree worm compost — —

50 g/tree 9 : 18 : 27 6 g/tree 26 : 0 : 0 — — 200 g/tree 9 : 18 : 27 24 g/tree 26 : 0 : 0 — —

—

—

Glufosinate (Finale-bayer) —

— — Application

Rotovator Rotovator Rotovator

Glufosinate Glufosinate Glufosinate

— —

Rotovator Rotovator

Glufosinate

2 August 2003 26 September 2003 1 June 2004 19 July 2004 16 September 2004 22 October 2004

—

—

8 April 2005

200 g/tree organic 6 : 8 : 15 1000 g/tree worm compost 100 g/tree organic 6 : 8 : 15 —

200 g/tree 9 : 18 : 27

Application

Rotovator

Glufosinate

40 g/tree 26 : 0 : 0 —

— —

Rotovator Rotovator

Glufosinate Glufosinate

7 June 2005 27 July 2005

insecticides (Bogya et al., 2000; Epstein et al., 2000; Markó & Kádár, 2005 ); but see also Bogya and Markó (1999) . Other management aspects, such as groundcover management, also have an impact on ground-dwelling predators (Miñarro & Dapena, 2003; Mathews et al., 2004). However, no effects on predaceous beetles were found among conventional, abandoned and organic apple orchards by Pearsall and Walde (1995). The success of an apple orchard is greatly determined by effective fertilizer application and by tree-row management to avoid weed competition for water and nutrients (Merwin, 2003; Neilsen & Neilsen, 2003). There are many different tree-row management systems, each with a different effect on many aspects of the tree cultivation, such as tree growth and fruit production, nutrient supply and uptake, or incidence of pests and diseases ( Sullivan et al. , 1998; Utkhede & Hogue, 1998; Merwin, 2003; Dapena et al., 2006). Similarly, the fertilizer treatment used is crucial for tree growth and yield (Neilsen & Neilsen, 2003). In both cases, organic alternatives to conventional management are available. In the framework of a project to assess the multitrophic effects of organic versus conventional apple management strategies (Dapena et al., 2006), two types of fertilizer treatment (organic versus chemical) and two types of organic tree-row management (straw mulching and mechanical weed control) versus the conventional use of herbicide were compared. Apart from the direct effects on tree growth and production, these alternatives to conventional management could also have an impact on activity-density and biodiversity of epigeic fauna. In the present study, we compared the effect of these alternative methods on the activity-density and the biodiversity of ground-dwelling predaceous arthropods. Among the wide spectrum of taxonomic groups that can be sampled in apple

Glufosinate

orchards, we focused on potential predators due to their value as bioindicators (Irmler, 2003) and their important role as natural enemies of pests ( Sunderland & Samu, 2000; Sunderland, 2002; Urbaneja et al. , 2006 ). In the case of apple orchards, conservation and enhancement of epigeal predators may reduce numbers of pests such as the codling moth Cydia pomonella L. (Glen & Milsom, 1978; Riddick & Mills, 1994; Mathews et al., 2004). Therefore, present study aimed to elucidate the effect that two management practices (fertilizer treatment and tree-row management) could have on the activity-density and diversity of ground beetles (Coleoptera: Carabidae), rove beetles (Coleoptera: Staphylinidae), ants (Hymenoptera: Formicidae) and spiders (Araneae) in an apple orchard.

Materials and methods Study orchard and experimental design Field studies were carried out during 2003–2005 in an experimental orchard at Servicio Regional de Investigación y Desarrollo Agroalimentario (SERIDA), Villaviciosa, Asturias, north-west Spain (43°30⬘N, 5°30⬘W, 15 m a.s.l.). A 0.3-ha orchard was planted in March 2003 with apple trees distributed in six rows, with each row consisting of trees of a different combination of cultivar and rootstock. The local cider cultivars ‘De la Riega’ and ‘Solarina’ were planted on M.7, MM.106 and MM.111. No differences in size were detected among the different cultivar/rootstock combinations, and so no effect on arthropod capture, such as differential shade due to different canopy size determined by the cultivar or rootstock type (Lassau & Hochuli, 2004), was expected, as revealed in a preliminary analysis. Trees were planted in © 2008 The Authors

Journal compilation © 2008 The Royal Entomological Society, Agricultural and Forest Entomology, doi: 10.1111/j.1461-9563.2008.00403.x

Apple orchard management on ground predators 3 Table 2 Species captured in the pitfall traps, total number of individuals throughout the sampling period and relative percentage Species

n

%

Species

n

%

Aleochara spadicea (Erichson) Anotylus sp1

110

28.50

49

12.69

Staphylinus dimidiaticornis Geminger Xantholinus longiventris Heer Philonthus cognatus Stephens Atheta sp1

29

7.51

Pardosa proxima (C. L. Koch) Trochosa ruricola (De Geer) Trochosa sp.

24

6.22

22

5.70

13

3.37

Ocypus olens (Müller)

12

3.11

Stilicus orbiculatus Paykull Drusilla canaliculatus (Fabricius) Gabrius sexualis Smetana Paederus fuscipes Curtis Atheta sp2

11

2.85

Linyphiidae sp.

10

2.59

10

2.59

8

2.07

Erigone dentipalpis (Wider) Oedothorax apicatus (Blackwall) Erigoninae sp.

7

1.81

Linyphiidae

Platystethus sp1

7

1.81

Aleochara curtula (Goeze)

6

1.55

Atheta sp3

5

1.30

Gyrohypnus fracticornis (Müller) Phloeonomus pusillus (Gravenhorst) Scopaeus portai Luze

5

1.30

Pachygnatha degeeri Sundevall Pachygnatha clercki Sundevall Tetragnatha sp.

5

1.30

Metellina sp.

5

1.30

Tetragnathidae

Tasgius pedator Gravenhorst Philonthus sp

5

1.30

4

1.04

Tegenaria sp.

2

0.19

Atheta sp4

3

0.78

Agelenidae

2

0.19

Atheta sp5

3

0.78

Philonthus nitidicollis (Lacordaire)

3

0.78

Aleochara sp.

2

0.52

Anotylus sp2

2

Bolitocharini sp Leptolinus subangulatus Reitetr Ontholestes murinus (Linnaeus) Platystethus sp2

282

27.35

211

20.47

133

12.90

Pardosa sp.

30

2.91

Pardosa pullata (Clerck) Lycosidae

23

2.23

679

65.86

0.52

Trachyzelotes pedestris C. L. Koch Micaria pulicaria (Sundevall) Zelotes sp.

2

0.52

Gnaphosidae

2

0.52

2

0.52

2

0.52

Pholcus phalangioides (Fuesslin) Pholcidae

243

23.57

7

0.68

4

0.39

4

0.39

258

25.02

15

1.45

3

0.29

3

0.29

3

0.29

24

2.33

2

0.19

2

0.19

1

0.10

5

0.48

1

0.10

1

0.10

Species

n

Pseudophonus rufipes (DeGeer) Poecilus cupreus (Linnaeus) Carabus cancelatus (Illiger)

1578

55.84

498

17.62

291

10.30

99

3.50

92

3.26

58

2.05

42

1.49

36

1.27

18

0.64

14

0.50

12

0.42

11

0.39

10

0.35

9

0.32

9

0.32

5

0.18

5

0.18

4

0.14

4

0.14

4

0.14

4

0.14

3

0.11

3

0.11

2

0.07

2

0.07

2

0.07

2

0.07

2

0.07

1

0.04

Diachromus germanus (Linnaeus) Brachinus elegans Chaudoir Anisodactylus binotatus (Fabricius) Steropus gallega (Fairmaire) Pterostichus niger (Schaller) Clivina fossor (Linnaeus) Amara plebeja (Gyllenhal) Harpalus honestus (Duftschmidt) Tachys bistriatus (Linnaeus) Chrysocarabus lineatus (Dejean) Nebria brevicollis (Fabricius) Pterostichus vernalis (Panzer) Acupalpus dubius (Schilsky) Bembidion properans (Stephens) Agonum muelleri (Herbst) Agonum nigrum Dejean Anchomenus dorsalis (Pontoppidan) Platyderus quadricollis (Chaudoir) Bembidion quadrimaculatum (Linnaeus) Chlaenius nigricornis (Fabricius) Acupalpus notatus (Mulsant et Rey) Bembidion lunulatum (Geoffroy) Bembidion minimum (Fabricius) Microlestes minutulus (Goeze) Stenolophus skrimshiranus (Stephens) Agonum marginatum (Linnaeus)

%

© 2008 The Authors Journal compilation © 2008 The Royal Entomological Society, Agricultural and Forest Entomology, doi: 10.1111/j.1461-9563.2008.00403.x

4

M. Miñarro et al.

Table 2 Continued Species

n

Quedius semiobscurus Marsham Astenus misellus Mulsant et Rey Dinaraea angustula (Gyllenhal) Gymnusa sp

%

Species

2

0.52

1

0.26

1

0.26

1

0.26

1

0.26

Ozyptila sp.

1

0.26

Neobisnius sp

1

0.26

Oligota sp

1

0.26

Gyrohypnus wagneri Scheerpeltz Hypomedon propinquus Brisout

Oxitelus sp

1

0.26

Paederini sp

1

0.26

Platystethus sp3

1

0.26

Pseudocypus fuscatus Gravenhorst Quedius simplicifrons Fairmaire Scopaeus laevigatus Gyllenhal Stilicus rufipes Germar Tachinus sp.

1

0.26

1

0.26

1

0.26

1

0.26

1

0.26

1

0.26

Thinodromus sp.

Staphylinidae

386

100

Dysdera crocata C. L. Koch Dysderidae

n

%

Species

6

0.58

6

0.58

45

4.36

Ozyptila simplex (O. P.-Cambridge)

5

0.48

Ozyptila claveata (Walckenaer) Xysticus erraticus (Blackwall) Thomisidae

2

0.19

1

0.10

53

5.14

2

0.19

2

0.19

Robertus arundineti (O. P.-Cambridge) Theridiidae

Phrurolithus festivus (C. L. Koch) Corinnidae

Araneae

north–south rows separated by grass alleys. Distances were in the range 2.1–3.0 m between trees in a row and 5.0–6.0 m between rows, depending on the cultivar and rootstock vigour. The total number of trees per row was in the range 30–42. For the experimental design, each of the six tree rows was considered as a block. Then, each block was divided into two whole plots, and a different fertilizer strategy (organic or chemical) was randomly assigned to the whole plots within each block. Then, each whole plot was divided into three split-plots, and a tree-row management (mulching, tillage or herbicide) was assigned to the split-plots within each whole plot. Therefore, the design was a randomized complete block split-plot with a 2 × 3 arrangement and six repetitions. Consequently, a total of 36 measures were available for analysis. There were between five and seven trees in each split-plot. With regard to fertilizer application, two different strategies were used: organic and chemical. Approximately, the

1

0.10

1

0.10

1031

100

n

%

Agonum viridicupreum (Goeze)

1

0.04

Amara anthobia (A.y J.B. Villa) Cryobius cantabricus (Schaufuss) Harpalus affinis (Schrank) Pseudoophonus griseus (Panzer) Syntomus obscuroguttatus Duftschmid

1

0.04

1

0.04

1

0.04

1

0.04

1

0.04

Carabidae

Lasius niger (Linnaeus)

2826

100

639

86.94

Lasius emarginatus (Olivier)

43

5.85

Myrmica scabrinodis Nylander Hypoponera eduardi (Forel) Temnothorax unifasciatus (Latreille)

36

4.90

16

2.18

1

0.14

Formicidae

735

100

same quantities of nitrogen, phosphorus and potassium were applied in the organic and the chemical plots. Type of fertilizers and date of application are shown in Table 1 . With respect to the groundcover management, three types of treerow management strategies were performed: straw mulch (consisting of a layer of withered herb 15–20 cm thick); tillage (the plots were periodically tilled using a rotary plow); and herbicide (glufosinate-amonium (Finale, Bayer) was periodically applied) (Table 1). Each treatment extended approximately 0.70 m on either side of the row. The alleys were cleaned when necessary (three to four times per year) using a shredder. The two cider cultivars planted in this orchard are diseasetolerant and so no fungicides were applied to the trees. The only insecticide applied (to the whole orchard) was NeemAzal-T/S (Trifolio-M GmbH, Germany), which was used against the rosy apple aphid (Dysaphis plantaginea Passerini), in May 2003, May 2004 and April 2005. The plantation was not irrigated. © 2008 The Authors


Apple orchard management on ground predators 5 Table 3 Results of the split-plot analysis of variance testing the effects of the fertilizer treatment and the tree-row management on the activity-density of carabids, staphylinids, ants, spiders and the overall predator numbers Carabids

Staphylinids

Ants

Spiders

All predators

Source of variation

d.f.

F

P

F

P

F

P

F

P

F

P

Block Fertilizer (whole plot) Whole plot error Management (subplot) Fertilizer ´ management Sub plot error

5 1 5 2 2 20

1.44 2.04 0.69 25.12 0.47

0.351 0.212 0.637 0.000 0.629

0.64 3.41 1.57 6.97 1.14

0.684 0.124 0.215 0.005 0.341

1.72 0.31 0.89 0.34 1.48

0.283 0.599 0.504 0.718 0.251

2.62 2.29 1.05 15.25 2.91

0.157 0.191 0.416 0.000 0.078

1.17 0.16 1.42 18.23 1.61

0.435 0.707 0.261 0.000 0.225

Trapping of ground predators

seasonal differences in catches. Moreover, a previous analysis showed that the preference for different managements was quite constant along the sampling period. Most of the deviations in some sampling dates could be assigned to the dominance of a species with different specific preference for a given treatment. For the species-level data, a log( x + 1) transformation was used when necessary to meet the assumption of homoscedasticity. Community structure of the ground-dwelling predators was described by species richness (S) and Shannon–Wiener’s diversity index (H). These parameters were calculated for each of the 36 pitfall traps. Split-plot analysis of variance were undertaken to analyze the effect of the fertilizer treatment (whole plot factor) and of the tree-row management strategies (split-plot factor) in the arthropod captures and in the biodiversity parameters. Tukey’s tests were applied to compare treatment differences in the split-plot factor.

Ground beetles (Coleoptera: Carabidae), rove beetles (Coleoptera: Staphylinidae), ants (Hymenoptera: Formicidae) and spiders (Araneae) were collected in pitfall traps, which is probably the most efficient method of collecting grounddwelling invertebrates ( Coulson & Butterfield, 1985; Cameron et al., 2004). Traps of 8.5 cm in diameter containing a solution of detergent and ethanol to reduce the surface tension and preserve the arthropods were used. Traps were protected against rainwater with a roof tile. One trap was placed in each plot (n = 36). Traps were separated 15 m in the tree row and 9 m between adjacent rows. Ground predators were sampled once a month during summer and early autumn in 2003 (July, August, September and October), 2004 (July, August and September) and 2005 (June, July, August, September and October). The traps were active for a 7-day period on each sampling occasion. As flooding is frequent in winter and spring in the experimental orchard due to the low soil permeability, we did not to sample in that period.

Statistical analysis

Results

As we were primarily interested in observing the responses of predators to treatments, we decided to pool catch data from across all sample dates to obtain a unique value for each pitfall trap, and so marginalize the potential effect of

A total of 4978 individuals were identified. Carabids (56.8% of the total catches) were the most abundant taxon, followed by spiders (20.7%), ants (14.8%) and rove beetles (7.7%). As the study commenced soon after planting, it was possible to

Table 4 Split-plot analysis of variance testing the effects of fertilizer treatment and tree-row management on the activity-density of the species with more than 100 catches Poecilus cupreus Source of variation

Pseudophonus rufipes

Carabus cancellatus

Aleochara spadicea

Lasius niger

Pardosa proxima

Trochosa ruricola

Trochosa sp.

F

P

F

F

F

F

F

F

0.94 0.526 1.42 0.06 0.813 0.97

0.354 0.371

3.50 0.098 14.77 0.012

0.08 0.993 0.62 0.692 0.37 0.572 0.63 0.465

0.62 0.692 1.27 0.88 0.391 0.00

0.401 1.08 0.467 0.964 0.24 0.646

1.22 0.336 1.46

0.248

0.35 0.877

3.05 0.033 1.50 0.235

2.59 0.058 2.78

0.046 0.94 0.476

9.55 0.001 23.61 0.000

12.68 0.000

3.78 0.041 0.51 0.608

30.95 0.000 6.79

0.006 2.80 0.085

0.16 0.852

0.35 0.706 1.27 0.303

1.42 0.266 5.31

0.014 1.32 0.289

d.f. F

Block 5 Fertilizer 1 (whole plot) Whole plot 5 error Management 2 (subplot) 2 Fertilizer ´ management Sub plot error 20

P

1.13 0.344 0.00

0.996

P

P

P

P

P


P

6

M. Miñarro et al. Similarly, none of the identified spiders represented more than 30% of the catches, with Pardosa proxima (C.L. Koch) (27.3%), Trochosa ruricola (DeGeer) (20.5%) and Trochosa sp. (12.9%) comprising the three most common spiders. With respect to catches, the tree-row management factor was more important than the type of fertilizer applied (Tables 3 and 4). The fertilizer treatment only significantly affected the catches of the ground beetle C. cancellatus (Table 4), whose activity-density was higher in the chemically-treated plots. The groundcover management had a significant effect on the activity-density of all the analyzed taxa except total ants, the ant L. niger and the spider Trochosa sp. ( Figs 1, 2 ). However, the strategy that favoured activity-density depended greatly on the taxonomic group. Thus, carabids were predominantly caught in the herbicide and the tilled plots, staphylinids under the mulching and the herbicide plots, spiders in the tilled plots and total predators in the herbicidetreated and the tilled plots (Fig. 1). There were also differences in the preference at the species level (Fig. 2). The studied factors also influenced significantly the biodiversity parameters (Tables 5 and 6). The fertilizer strategy only affected the species richness of the rove beetles (Table 5), with more on the chemical plots. With respect to tree-row management, species richness was higher on the plots treated with herbicide for carabids and in the mulched plots for staphylinids (Fig. 3A). However, there were no significant differences in the abundance of all predators caught (Fig. 3A). With respect to Shannon–Wiener’s diversity, the index was significantly lower in the tilled plots for total predators and for the carabids (Fig. 3B). In the case of the staphylinids, this parameter was significantly greater on the mulched plots (Fig. 3B). As Linyphiidae could not be identified to species level, this family of spiders was not considered in the analysis of species richness and Shannon–Wiener’s diversity.

250 Mulching Tillage Herbicide

Captures/trap

200

a a

150

a a b

100

b

50

a

b ab

a

a

a

a

b

b

0

ids

rab

ds

ts

lini

hy

Ca

p Sta

rs

rs

An

ato

ide

red

Sp

p All

Figure 1 Effect of tree-row management on the captures of carabids, staphylinids, ants, spiders and total predators (mean captures/trap over the sampling period). Error bars correspond to standard errors. For each taxonomic group, columns with the same letter are not significantly different.

study the sequence of the orchard colonization by the different taxa. In the first year, carabids (39.7%) and spiders (35.8%) were caught in the same number, although, in the first sample (approximately 4 months after planting), the activity-density of spiders was slightly higher than that of carabids. In 2004 (65.7%) and 2005 (66.0%), carabids were numerically dominant. Rove beetles were represented by 46 species, ground beetles by 35, spiders by 23 (Linyphiids could not be identified up to species level) and ants by five (ten queens from four different ant species were also caught, but not considered in the analysis because they could have arrived by flying and not be affected by the treatments). A complete list of the species and their abundance is presented in Table 2. Only eight species were represented by more than 100 individuals. Among carabids, Pseudophonus rufipes (De Geer) (55.8% of the total carabid catches), Poecilus cupreus L. (17.6%) and Carabus cancellatus (Illiger) (10.3%) were the most common species ( Table 2 ). Among ants, Lasius niger (L.) clearly dominated the catches (86.9%). On the other hand, the most frequently-collected staphylinid, Aleochara spadicea (Erichson) only represented 28.5% of these beetles.

Discussion Conventionally, apple trees receive chemical fertilizer, and weeds in the tree-row are suppressed by herbicide sprays. Alternatives to this conventional management are required to produce apples organically. Organic fertilizers are available

Captures/trap

100 Mulching

a

75

0

s

ipe

ho

Ps

uf sr

nu

b b us

re up sc

ilu

ec

Po

a

a

b

25

op

Herbicide

a

50

c

d eu

Tillage

bu

ra Ca

sc

b

us

lat

ce an

ara

ch

o Ale

a

a

a a

r

ige

n ius

s

La

b

c

a

ice

ad sp

a

ab a

xim

s

rdo

Pa

ro ap

a os

ur ar

a a a .

la

ico

ch

Tro

a ab

b

Tro

a os ch

sp

Figure 2 Effect of tree-row management on the captures of species with more than 100 individuals captured (mean captures/ trap over the sampling period). Error bars indicate standard errors. For each species, columns with the same letter above the column are not significantly different. Analysis were performed on log( x + 1) transformed data but are presented as raw data here. © 2008 The Authors


Apple orchard management on ground predators 7 Table 5 Split-plot analysis of variance testing the effects of fertilizer treatment and tree-row management on the species richness Carabids

Staphylinids

Ants

Spiders

All predators

Source of variation

d.f.

F

P

F

P

F

P

F

P

F

P


5 1 5 2 2 20

0.71 1.12 1.12 10.00 0.18

0.641 0.338 0.380 0.001 0.836

2.81 7.86 0.50 15.22 0.83

0.141 0.038 0.776 0.000 0.451

2.39 5.87 0.46 0.10 0.70

0.180 0.060 0.801 0.905 0.508

1.00 0.22 0.54 0.00 0.19

0.500 0.656 0.744 1.000 0.170

3.97 1.66 0.66 2.64 1.29

0.078 0.255 0.654 0.096 0.297

As Linyphiidae identification could not be performed up to species level, this family of spiders was not considered in the analysis.

Modification of microhabitat by groundcover management may explain the specific reactions of different taxa. In the experimental orchard, soil moisture was significantly greater under mulching whereas temperature was lower (Dapena et al., 2006), which could influence activity-density of some predaceous arthropods (Lassau & Hochuli, 2004; Hatten et al., 2007). Moreover, grass residues of mulching may be an impediment for movement of some species as well as a food resource or a shelter for some other species (Langellotto & Denno, 2004; Hatten et al., 2007). Regarding tillage is clear that this management transforms the soil conditions with respect to the other treatments (Cárcamo, 1995; Hatten et al., 2007). Herbicides may affect arthropods mediated by habitat changes, such as the plant community (Taylor et al., 2006). Therefore, groundcover management modifies the environment producing different conditions and microhabitats. Because each species has its own ecological and physiological requirements, species may display a differential response depending on groundcover suitability and their own requirements, as our data and other studies have shown ( Fig. 2 ) ( Cárcamo, 1995; Miñarro & Dapena, 2003; Lassau & Hochuli, 2004; Mathews et al., 2004; Hofmann & Mason, 2006; Tuovinen et al., 2006; Hatten et al., 2007; Thomson & Hoffmann, 2007). A previous study in another apple orchard also showed a preference of the two most abundant carabids P. rufipes and P. cupreus for tillage and plots with herbicide treatment, respectively (Miñarro & Dapena, 2003). However, a possible bias in pitfall catches due to different habitat structure should be considered, as has been shown in the capture

in form of manure or compost, but also as pelletized fertilizers obtained from animal and vegetal wastes, such as some of the applied in the present study in the experimental orchard. Different types of mulching or a mechanical control of weeds are alternatives to the use of herbicide. The results of our research showed that these two tested management factors (particularly tree-row management) may affect both activitydensity and biodiversity of ground-dwelling potential predators. The impact of the fertilizers was much lower than groundcover management. With regard to catches of the different taxonomic groups and the most-frequently caught species, there was only an effect on the carabid C. cancellatus , which showed a higher activity-density on the chemicallytreated plots. Chemical application also favoured the species richness of rove beetles. Therefore, the change from chemical to organic fertilizer may be performed without a significant negative effect on the overall ground-dwelling predators. However, the strategy followed to avoid weed competition in the rows of trees had a strong influence on sampled arthropods. Regarding abundance, ants were the only taxon not affected by treatment because ant catches are probably influenced by the distance to the nest rather than by groundcover management. Foraging distances are known to reach up to 10 m from the nest in L. niger and 2 m in Myrmica scabrinodis (Schlick-Steiner et al., 2006). For the other taxa, the effect of the tree-row management was different.

Table 6 Split-plot analysis of variance testing the effects of fertilizer treatment and tree-row management on the Shannon–Wiener’s diversity index Carabids

Staphylinids

Ants

Spiders

All predators

Source of variation

d.f.

F

P

F

P

F

P

F

P

F

P


5 1 5 2 2 20

1.17 2.43 1.28 9.88 0.07

0.435 0.180 0.312 0.001 0.933

1.31 2.75 0.95 12.98 1.57

0.386 0.158 0.470 0.000 0.232

1.26 4.88 1.29 0.06 0.76

0. 403 0.078 0.309 0.943 0.479

0.80 0.01 0.31 0.52 0.72

0.594 0.946 0.899 0.602 0.500

1.05 1.26 0.75 11.72 0.70

0.481 0.313 0.594 0.001 0.510

As Linyphiidae identification could not be performed up to species level, this family of spiders was not considered in the analysis. © 2008 The Authors Journal compilation © 2008 The Royal Entomological Society, Agricultural and Forest Entomology, doi: 10.1111/j.1461-9563.2008.00403.x

8

M. Miñarro et al.

(B) 3,5

(A) 30,0 Mulching Tillage Herbicide

a

a

2,5

20,0 15,0

a 10,0

b

b

Mulching Tillage Herbicide

3,0

a Diversity (H)

Species richness (S)

25,0

a

a

b

b

a a a b

1,0

a a a

b b 5,0

a

a b

a

2,0 1,5

a

a a a

0,5

a a a

0,0

0,0 Ca

ra

s bid S

h tap

yl

ds ini

ts An

Sp

rs ide All

d pre

rs ato

ra Ca

bid

s S

h tap

ylin

ids

An

ts Sp

ide

rs All

d pre

ato

rs

Figure 3 Effects of tree-row management on (A) species richness (S) and (B) Shannon–Wiener’s diversity index (H) (mean captures/trap over the sampling period). Error bars correspond to standard errors. For each species, columns with the same letter above the column are not significantly different.

rate of carabids species between tilled and nontilled plots (Hatten et al., 2007). Tillage has been considered as one of the most disrupting agricultural practices, but its impact is largely dependent on the crop, species or taxa (Cárcamo, 1995; Hummel et al., 2002; Andersen, 2003; Motobayashi et al. , 2006; Hatten et al., 2007). In this and in a previous experiment (Miñarro & Dapena, 2003), soil was tilled several times throughout the sampling period, and a highly disturbing effect could be expected. By contrast, only the tree row was tilled and the recruitment from alleys could diminish the potential disturbing effect. In any case, the impact on the arthropod fauna (i.e. positive as well as negative) was very specific and not greater than that of the other management systems ( Figs 1, 2 ) (Miñarro & Dapena, 2003). As the total predators response is driven by the much higher proportion of carabids (Fig. 1), activity-density was lower under mulching, which only favoured staphylinids. However, for the biodiversity parameters, species richness was not different among treatments, whereas Shannon – Wiener’s index was greater on the mulched and the herbicide plots. Therefore, comparing organic versus conventional management, the replacement of herbicide with mechanical weed control did not affect catches of predators, whereas abundance was lower under mulching. The change from conventional to organic tree-row management did not affect species richness, whereas Shannon–Wiener’s index of carabids lower when changing to tillage. The effect on captures and biodiversity parameters depended on the taxonomic group. Interestingly, the species richness of carabids decreased with mulching whereas diversity increased as a consequence of a lower dominance of particular species (Fig. 3). Some studies have compared the effects of chemical and organic management in different crops. Shah et al. (2003) found more carabids but less staphylinids in organic than in conventional farms, but a higher dominance of particular species in organic farms was translated to a lower diversity in

organic systems. Studying carabids on forage grain, Melnychuk et al. (2003) found no differences in species diversity or in abundance between high input and organic systems. In vineyards, abundance of carabids and spiders was greater in mulches than with herbicide application, whereas there was no difference in staphylinid catches (Thomson & Hoffmann, 2007). Different responses of carabids and spiders were found when comparing chemical and biological insecticides in vegetable production: spider catches were lower in chemically-treated plots, whereas carabids were not affected by insecticide (Hummel et al., 2002). Management effects may depend strongly not only on species, but also on functional groups: predator activity-density was greater in conventional fields whereas detritivores were more abundant in organic fields (Clough et al., 2007). The conservation and enhancement of biological control by naturally-occurring enemies is considered a key point in the management of agricultural pests (Landis et al., 2000; Boller et al., 2004; Zehnder et al., 2007). The present study showed how management practice is an important factor in conserving ground-dwelling arthropods in apple orchards and how biodiversity may be enhanced with a specific practice. However, each taxonomic group reacts specifically to particular treatments. From a practical point of view, a precise knowledge of the role that each taxon (including the species level) plays as a biocontrol agent is needed to favour its activity-density and the biological control of apple pests.

Acknowledgements We thank Tania Iglesias, Iván Fernández and Gabriela Fernández-Mata for their help in the sampling, and Mark Brown, Enrique Dapena, Linda Thomson and referees for comments on an earlier draft of the manuscript. This research was supported in part by the Government of the Principado de Asturias (Project FICYT PC-04 56). © 2008 The Authors


Apple orchard management on ground predators 9

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