(Coleoptera, Elateridae) in Arable Land After Abandonment

Biologia, Bratislava, 62/1: 103—111, 2007 Section Zoology DOI: 10.2478/s11756-007-0017-4

Population dynamics of wireworms (Coleoptera, Elateridae) in arable land after abandonment

Pavel Jedlička1,2 &JanFrouz3*

1Institute of Organic Chemistry and Biochemistry, Academy of Science of the Czech Republic, Flemingovo náměstí 2, CZ–16610 Praha 6, Czech Republic 2Charles University, Faculty of Science, Department of Ecology, Viničná 7,CZ–12843 Praha 2, Czech Republic 3Institute of Soil Biology, Biological Center, Academy of Sciences of the Czech Republic, Na Sádkach 7,CZ–37005 České Budějovice, Czech Republic; e-mail: [email protected]

Abstract: The community of elaterid larvae of three sites (field and two fallows), representing different stages of secondary succession, were studied using soil sampling from 1986 to 1993. All three sites were abandoned arable land: a field cultivated until 1991, a fallow I abandoned in 1986, and a fallow II abandoned about 1976. The fallow II was used as a meadow after abandonment and was regularly mown until 1985, when cultivation stopped. Six species of Elateridae larvae were found at all three study sites. In the field, Agriotes obscurus, Athous niger, Athous subsuscus, Dalopius marginatus and Athous vittatus were found, A. niger and A. obscurus being the most abundant species. During cultivation, larval densities were very low, however, larval abundance increased up to 8.8 ± 8.3 ind. m−2 when cultivation stopped. Only small A. obscurus larvae were found during cultivation, whereas larval size increased after abandonment. In fallow I A. obscurus, A. niger, A. subsuscus, D. marginatus,andAgrypnus murinus were found and the average annual abundance fluctuated between 0.8 ± 1.4to40.8 ± 10.9 ind. m−2 with A. obscurus being the most abundant species. Fallow II supported the highest densities of wireworms from all plots studied (71.2± 35.2 to 280.0± 24.8 ind. m−2). A. obscurus, A. niger, A. subsuscus and D. marginatus were found in fallow II. The abundance of all larval Elateridae as well as the dominant species A. obscurus decreased during the study period, while simultaneously the occurrence of small sized A. obscurus larvae decreased. The frequency of cultivation and time elapsed since last cultivation appeared to be the most important factors affecting elaterid occurrence in the field and fallow I. In fallow II, the decrease in abundance correlates with the accumulation of a dense litter layer, which may correspond with soil surface structure, plant community changes or predator pressure. Key words: succession; soil fauna; crop rotation; Agriotes obscurus; Athous niger

Introduction which may remain unmown for many years (Mašková et al. 2001). However, there is little known about the Larvae of Elateridae, also known as wireworms, repre- effect of long-term field and meadow abandonment on sent important pests in many agricultural crops (Rusek the community of soil dwelling elaterid larvae. 1972; Lefko 1998; Parker 2000; Rotrekl 2000; Parker & In addition to these practical implications, the Howard 2001; Parker et al. 2002). The setting aside and study of changes in communities of organisms is im- turning of arable land into grassland increases the oc- portant for a better insight into the functioning of eco- currence of wireworms (Lefko 1998; Parker 2000). Thus logical succession. In animal communities and particu- the extensification of plant production, which is applied larly in soil invertebrates, more empirical data on suc- in many countries with developed agriculture, may in- cessional community changes are needed for a better crease the occurrence of wireworms and their damage understanding of the underlying mechanisms of succes- to field crops. In the Czech Republic, the proportion sional changes. This represents one part of an exten- of fallows has increased recently in connection with sive research project dealing with successional changes recent socio-economical changes (Lipský 2000; Míchal of a wide spectrum of soil organisms (Frouz 1997; 2002). Many of these sites have now been abandoned Tajovský 1999; Pižl 1992). Preliminary studies indicate for more than 20 years and spontaneous succession has that Elateridae belong to the most important families resulted in the development of permanent grassland or of Coleoptera on these plots (Jedlička & Frouz 1999). woody vegetation. The extensification of plant produc- The main aim of this study was to investigate how tion, namely in low production areas, affects meadows, does the community of elaterid larvae change after field

* Corresponding author

c 2007 Institute of Zoology, Slovak Academy of Sciences 104 P. Jedlička & J. Frouz and meadow abandonment and which ecological factors For A. obscurus, a sample of 50 larvae covering all avail- were correlated with these changes. able sizes was weighed to an accuracy of ±0.01 mg using a Sartorius laboratory balance. From these measurements a linear regression between body length and mass was em- Study area and methods ployed. The R2 of regression used for the biomass calcula- tion were ≥ 0.9andP<0.05. For the remaining species, The study area was located in Southern Bohemia near every specimen was weighed. Before biomass determination Vodňany town, at Dlouhá Ves village (49◦06 N, 14◦07 E, ◦ the larvae were quickly dried by touching them with filter 570 m a.s.l.). The average annual temperature is 7.3 C, the paper. The abundance of larvae was expressed as number mean annual rainfall 605 mm. Three types of habitats were of individuals per square meter, for calculating the mean, studied: field, fallow I and II, representing different stages annual values for individual years from May to May pe- of secondary succession. All these sites were originally part riodswereused.OnewayANOVAwasusedtocompare of one large field which were piece by piece abandoned at species abundances and biomass and the biomass of individ- different times. The field was cropped with wheat in 1986, ual larvae among individual sampling years, based on larval potatoes in 1987, barley in 1988, oats, peas and clover in abundance or biomass in individual samples. Abundance or 1989 and clover in 1990. The terms of autumnal tillage in biomass data were log(n + 1) transformed to approach nor- 1988 were extremely late (25 November). In autumn of 1990, mality (Sokal & Rohlf 1981) before performing ANOVAs. the field was tilled for the last time and then abandoned. The Levene statistic was applied before ANOVA to test for The dominant plant species after abandonment were Rumex homogeneity of variance. If the ANOVA indicated signifi- obtusifolius DC. and Cirsium arvense Scop. In the follow- cant differences, LSD post hoc tests were used to test differ- ing years Agropyron repens L. became the most dominant ences between individual treatments. In the text, ANOVA plant species. The fallow I originally formed part of the output is presented in the form (ANOVA, df, F , P values cultivated field described above and was abandoned in au- for whole ANOVA; LSD P level for post hoc test). To study tumn 1985. In the two initial years of succession annual the relationships of dominant species abundance and fluctu- weeds were dominated by Appera spica-venti (L.) Beauv. ation in environmental parameters, a linear regression was forming the plant cover. Later, the vegetation was domi- used. PCA was used to visualize the main trends in the nated by tall grasses, especially by Calamagrostis epigejos community of Elateridae larvae, the main ordination axis Roth. The amount of litter which accumulated on the soil −2 −2 were then correlated with environmental data, the compu- surface increased from 19 g m in 1986 to 731 g m in tation was performed using CANOCO for Windows 4.0 (Ter 1993 (Frouz 1997). The fallow II was originally a culti- Braak & Šmilauer 1998). Log n + 1 transformed abundance vated field that bordered the previous plot, and was aban- values were used for PCA. Species which were found in only doned between 1975 and 1977. It was regularly mown until one site, with fewer than 3 individuals, were excluded from 1985. Its plant community was dominated by Holcus mol- the PCA. For all other statistics, SPSS10.0 was used (SPSS lis L., Holcus lanatus L., Agropyron repens and Trifolium 1999). Numbers after the symbol ± means SD. repens L. For more detailed information on these plots see Matějka (1990), Pižl (1992) and Frouz (1994, 1997). Data on soil moisture, rainfall and air temperature were taken from Results Frouz (1994) and data on litter from Frouz (1997), the data on plant cover from Matějka (1990) and Frouz (1997) (see Community structure these references for a more detailed description of method- A total of six species of Elateridae larvae: Agriotes ob- ology). Briefly, moisture data were based on soil sampling scurus L., 1758, Athous niger L., 1758, Athous subfus- (two samples per plot and sampling instance) and gravi- cus Müller, 1767, Athous vittatus F., 1792, Dalopius metrical determination of moisture. Soil temperature was measured in the morning (8–9 AM) at each site during each marginatus (L., 1758) and Agrypnus murinus (L., 1758) sampling occasion. Rainfall data were collected by a mete- were recorded in the study plots. orological station located about 1 km from the plots. Litter Field. The overall abundance of Elateridae larvae −2 was collected in each plot during autumnal sampling (five fluctuated from 0 to 22.4 ind. m (Fig.1A),withan samples area 625 cm2 per plot) dried and weighed. Vegeta- average 4 ± 4.7 ind. m−2, which is the lowest value of tion cover was estimated by a trained botanist during the average abundance on all the study plots. This average summer sampling period. value differs significantly from both fallows (ANOVA, To study Elateridae larvae, five circular soil samples df 22, F =46.84, P<0.001, LSD test P<0.05). The (625 cm2 area, 10 cm depth) were taken on each sampling abundance of Elateridae larvae was lower in the first five occasion by soil corer. Samples were taken at each site at four times per year (February, May, August and Novem- years of observation where the field was regularly tilled. ber) from May 1986 to February 1993. Soil samples were Compared to the period with and without cultivation, transported in the laboratory and extracted in a modified significantly (t-test, df 26, t = −2.59, P =0.015) higher Meyer extractor (Meyer 1980). The larvae were fixed by 1– values were found in the two years after field abandon- 2% formaldehyde, hand sorted and stored in 80% ethanol. ment (Table 1, Fig. 1A). When the field was cultivated In total, 1760 elaterid larvae were trapped and processed a higher abundance was usually found in May and Au- in this study. All larvae were identified to species level us- gust, whereas a zero value was typically recorded in ing Rudolph (1974) and Masler (1982). The length of ev- November and February (Fig. 1A). The only exception ery specimen (from front tip of head to end tip of uro- was November 1988 when the field was tilled after sam- gomph) was measured to an accuracy of 0.5 mm. Head capsule widths, to estimate instar number, were measured pling. After field abandonment, the highest values were to an accuracy of 0.014 mm in a sample of 400 larvae of recorded in August but larvae were also recorded in Agriotes obscurus. To determine larval biomass wet weight, some winter samples (Fig. 1A). The total biomass fluc- specimens stored in ethanol were used (Gaston et al. 1996). tuated from 0 to 167.4 mg m−2 (Fig. 2A). The commu- Elateridae in old fields 105

25 A 20

-2 15 10 Ind. m 5 0 II II II II II II II. V V V V V V XI XI XI XI XI XI V. XI. VIII VIII VIII VIII VIII VIII VIII. 1986 1987 1988 1989 1990 1991 1992

80 B 60 -2 40

Ind. m 20 0 II II II II II II II. V V V V V V XI XI XI XI XI XI V. XI. VIII VIII VIII VIII VIII VIII VIII. 1986 1987 1988 1989 1990 1991 1992

400 350 C 300

-2 250 200

Ind. m 150 100 50 0 II II II II II II II. V V V V V V XI XI XI XI XI XI V. XI. VIII VIII VIII VIII VIII VIII VIII. 1986 1987 1988 1989 1990 1991 1992 Years

Agriotes obscurus Athous niger Dalopius marginatus others

Fig. 1. Abundance of Elateridae larvae (ind. m−2) in individual sampling occasions in field (A) fallow I (B) and fallow II (C) during the observation period. nity consisted of five species where Athous niger and during the first year after abandonment, but during the A. obscurus were the most abundant (Table 1). These second year of observation the abundance of Elateridae species represent 65.7 (A. niger) and 17.1% (A. obscu- increased suddenly (Fig. 1B). The highest annual aver- rus) of all elaterid larvae found and their changes in age abundance was found in the last year of observation abundance follow a similar trend to total abundance. (Table 1). The seasonal changes of abundance on this Because both larval body length and head width show plot did not show any consistent pattern during the a considerable amount of variability, which prevents us study period (Fig. 1B). The total biomass of Elateri- from determining larval instars (Fig. 3), we rely on the dae larvae fluctuated from 0 to 302.3 mg m−2;biomass determination of the stage of larval development and fo- values gradually increased with an increasing time from cusonlyonlarvalgrowthmeasuredbylarvallengthand abandonment (Fig. 2B). The community consists of five biomass. Only small larvae of A. obscurus (up to 8 mm) species (Table 1). A. obscurus was highly dominant rep- were found in the field; during the period of cultivation resenting 90.1% of all larvae found and thus changes to the larvae were even smaller (up to 4 mm). Agriotes ob- A. obscurus abundance correspond with changes in to- scurus average mean larval biomass seems to be higher tal abundance of Elateridae described above. The aver- after abandonment but these differences are not statis- age mean larval biomass of A. obscurus increased with tically significant (ANOVA) (Fig. 4A). In A. niger,the time elapsed from abandonment in the range from 0.5 average mean larval biomass did not change between to 9.0 mg in 1987 and 1991, respectively (Fig. 4B). the periods when the field was cultivated and aban- Fallow II. The abundance of Elateridae larvae doned (t-test). The mean larval biomass in the third fluctuated from 19.2 to 345.6 ind. m−2 with an aver- year of observation was significantly higher than in the age 179.1 ± 68.9 ind. m−2, which was the highest value last two years of observation; in other years, no signifi- from all investigated plots (ANOVA, df 22, F =46.8, cant differences were found (Fig. 4A). P<0.001, LSD test P<0.054). Abundance decreased Fallow I. The overall abundance fluctuated from during the observation period (Fig. 1C, Table 1). The 0to73.6ind.m−2, with an average 18.4±16.9 ind. m−2 biomass of Elateridae larvae fluctuated from 343.4 to (Fig. 1B). The abundance of Elateridae was the lowest 2252.9 mg m−2. Similarly to fallow I, the seasonal 106 P. Jedlička & J. Frouz

Table 1. Mean abundance (ind. m−2) of Elateridae larvae in individual observation years and the whole observation period in ﬁeld fallow I and fallow II.

Field 1986 1987 1988 1989 1990 1991 1992 Mean FPSum of ind.a

Agriotes obscurus 0.8ab 0a 0.8ab 0a 0a 2.4b 0.8ab 0.7 2.36 0.034 6 Athous niger 0.8 0 1.6 0.8 3.2 4.8 7.2 2.9 23 Athous subfuscus 0 0 0 0 0 0.8 0 0.1 1 D. marginatus 0 0 1.6 0 0 0.8 0 0.3 3 Athous vittatus 000 01.6000.2 2

Elateridae 1.6a 0a 4ab 0.8a 4.8ab 8.8c 8c 4 2.96 0.009 35

Sum of individuals 2 0 5 1 6 11 10

Fallow I

Agriotes obscurus 0.8 32 8 11.2 13.6 12.8 37.6 16.6 145 Athous niger 0a 0a 0.8ab 0.8ab 0a 2.4b 0a 0.6 4.62 < 0.001 5 Athous subfuscus 000 0 0 00.80.1 1 D. marginatus 0 0 0 1.6 0.8 2.4 2.4 1 9 Agrypnus murinus 0 0.8 0 0 0 0 0 0.1 1

Elateridae 0.8a 32.8bc 8.8ab 13.6ab 14.4ab 17.6abc 40.8c 18.4 4.71 < 0.001 161

Sum of individuals 1 41 11 17 18 22 51

Fallow II

Agriotes obscurus 198.4cd 261.6d 160.8bc 172.8bc 114.4ab 152.8bc 68.8a 161.4 7.59 1409 Athous niger 3.2 11.2 4 13.6 6.4 4.8 0.8 6.3 55 Athous subfuscus 5.6 4 1.6 1.6 4 4.8 0.8 3.2 28 D. marginatus 17.6 3.2 0.8 0 21.6 13.6 0.8 8.2 72

Elateridae 224.8bc 280c 167.2b 188b 146.4ab 176b 71.2a 179.1 7.59 < 0.001 1564

Sum of individuals 281 350 206 235 183 220 89

Explanations: Statistically homogenous group of individual taxa among sampling years are marked by the same letters (ANOVA, LSD test, P<0.05), F and P values for whole ANOVA are given in the table, df is 139 in all cases, non significant F and P values were omitted. aSum of individuals – total number of larvae of given species or trapped on given site number of larvae in individual occasion can by calculated from abundance, one larva represent mean annual abundance 0.8 ind. m−2. changes of abundance on this plot did not show any dae larvae correlated in time from the last tillage on a consistent pattern during the study period but the dif- given plot, the average annual temperature in a given ferences between individual seasonal aspects were the year, the average rainfall in a given year, the maximum lowest from all plots (Fig. 1C). The community of Ela- amount of litter measured in the given year on given teridae larvae consists of four species, A. obscurus be- plots, the plant cover and moisture in observed individ- ing the most dominant, representing 90.1% of all larvae ual sampling terms (Table 2). found. The pattern of its abundance is similar to the A significant positive correlation was found on pattern of total abundance described above. The mean the field between the year of observation (r =0.440; larval biomass of A. obscurus increased with time dur- P<0.05 and r =0.433; P<0.05), the time from ing which the plot was not used as a mown meadow tillage (r =0.559; P<0.01 and r =0.519; P<0.01) (Fig. 4C). and the amount of litter (r =0.467; P<0.01 and Only two other species of elaterid larvae, i.e., r =0.477; P<0.01) with both total Elateridae abun- Dalopius marginatus and Athous subfuscus,markedly dance and abundance of Athous niger, respectively. In influenced the overall abundance and biomass values fallow I, no significant correlation between the inves- on all plots. Their higher presence was ascertained in tigated environmental parameters and the total abun- Fallow I and II (D. marginatus) and in Fallow II (A. dance of Elateridae larvae was found. Athous subfus- subfuscus) only (Table 1, Fig. 1). While mainly small cus indicated a positive correlation with temperature size larvae of D. marginatus (3–4 mm) had a relatively (r =0.365; P<0.05). Dalopius marginatus display a high mean abundance (Table 1, Fig. 1C) but rather significant positive correlation with the year of obser- minor proprortion in overall biomass (Fig. 2C), larger vation (r =0.458; P<0.05), the time from tillage (r = larvae of A. subfuscus showed a distinct rate in biomass 0.464; P<0.05), the current temperature (r =0.458; in fallow II (Table 1, Fig. 2C). P<0.05) and soil moisture (r =0.458; P<0.05). In fallow II, the abundance of both all Elateridae larvae Correlation of community changes with environmental and A. obscurus displayed a significant negative correla- factors tion with the year of observation (r = −0.599; P<0.01 The abundance of individual species and all Elateri- and r = −0.627; P<0.01), the time from tillage Elateridae in old fields 107

180 160 A 140 120 -2 100 80 mg m 60 40 20 0 II II II II II II II. V V V V V V XI XI XI XI XI XI V. XI. VIII VIII VIII VIII VIII VIII VIII. 1986 1987 1988 1989 1990 1991 1992

350 B 300 250

-2 200 150 mg m 100 50 0 II II II II II II II. V V V V V V XI XI XI XI XI XI V. XI. VIII VIII VIII VIII VIII VIII VIII. 1986 1987 1988 1989 1990 1991 1992

2500 C 2000

-2 1500

mg m 1000

500

0 II II II II II II II. V V V V V V XI XI XI XI XI XI V. XI. VIII VIII VIII VIII VIII VIII VIII. 1986 1987 1988 1989 1990 1991 1992

Agriotes obscurus Athous niger Athous subfuscus Dalopius marginatus

Fig. 2. Biomass of Elateridae larvae (mg m−2) in individual sampling occasions in ﬁeld (A) fallow (B) and fallow II (C) during the observation period. 160 140 120 100 80 60

Number of larvae of Number 40 20 0 2 5 8 111417202326 Body lenght (mm)

10 Number of larvae of Number 5

0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 Width of head (mm)

Fig. 3. Body length and head width of Agriotes obscurus larvae (mm) based on larvae collected during the whole observation period in all sites. 108 P. Jedlička & J. Frouz

Table 2. Linear correlation coeﬃcient between environmental variables and individual species and whole family Elateridae.

Plot/species Time Time from tillage T Litter Moisture

Field Athous niger 0.433* 0.519** 0.002 0.477** 0.033 Elateridae 0.440* 0.559** 0.014 0.467** 0.057

Fallow I Athous subfuscus 0.322 0.328 0.365* 0.322 −0.075 Dalopius marginatus 0.458* 0.464** 0.458* 0.236 0.458*

Meadow Agriotes obscurus −0.627** −0.632** −0.219 −0.595** 0.091 Elateridae −0.599** −0.603** −0.164 −0.567** 0.011

Explanations: Only correlation for taxa that show at least one statistically signiﬁcant correlation coeﬃcient with considered environmental variables are given. * P<0.05, ** P<0.01, T – average annual temperature.

35 A b 30 25 20

mg ab 15 10 a a 5 ab ab 0 1986 1987 1988 1989 1990 1991 1992

10 c 9 B 8 7 bc 6 5 ab

mg b 4 abc 3 ab 2 a 1 0 1986 1987 1988 1989 1990 1991 1992

14 12 c c c C 10 bc 8 bc ab mg 6 a 4 2 0 1986 1987 1988 1989 1990 1991 1992

Agriotes obscurus Athous niger

Fig. 4. Mean larval biomass (mg) of Agriotes obscurus and Athous niger in individual years in ﬁeld (A) fallow I (B) and fallow II (C). Statistically homogenous group among individual taxa and sampling site are marked by the same letters (ANOVA. LSD test. P<0.05); df is 139 in all cases, F and P values were: 2.14 and 0.05 for A. niger in ﬁeld; 2.92 and < 0.0001 for A. obscurus in fallow I.

(r = −0.603; P<0.01 and r = −0.632; P<0.01) cession age (field – fallow I – meadow). The time since and the amount of litter (r = −0.565; P<0.01 and the last tillage, plant cover, soil moisture and amount r = −0.595; P<0.01). of litter display a strong positive correlation with the PCA was used to find the main trends in com- first ordination axis (Fig. 5) (the correlation coefficients munity changes on all study plots (Fig. 5). The first were: 0.86, 0.53, 0.58 and 0.57). The occurrence of A. and second ordination axes together explain 82.3% of obscurus correlated positively with all these environ- species data variability, (69.5% 1st axis and 12.8% 2nd mental factors, the closest correlation can be found be- axis). The investigated sites are ordinate according to tween A. obscurus and time from last tillage. Athous the first ordination axis according to the increasing suc- subfuscus and D. marginatus display similar trends as Elateridae in old fields 109

Fig. 5. PCA of community of Elateridae larvae in individual sampling sites and sampling occasions. Solid arrows represent species, dashed lines represent inﬂuence of environmental variables. Moisture – soil moisture (% of water in mass of wet soil), litter – the amount of litter on soil surface (g m−2), plant cover – % of soil covered by plants; based on data given by Frouz (1997) and Matějka (1992).

A. obscurus. However, A. niger seems to be quite in- arable crops in British Columbia and Washington. How- dependent from position of the plot on the succession ever, Rusek (1967, 1972) mentioned that Agriotes brevis gradient as well as from environmental factors that cor- Candéze, 1863 was a dominant species in arable land in respond with the first ordination axis. the Czech Republic, where A. obscurus was less abundant. Masler (1982) mentioned A. brevis as a dominant Discussion species in arable land in Slovakia. Athous niger is of- ten found in arable land but usually at low abundance In agreement with other authors (Lefko 1998; Parker (Rusek 1967, 1972; Strüeve-Kusenberg 1981). The ab- 2000), the results of this study indicated that field aban- sence of another important elaterid pest species – Agri- donment and formation of plant cover increased the otes lineatus (L., 1767) in our samples and generally is abundance of Elateridae larvae in the abandoned field in agreement with the lower occurrence of this species in and thus enhanced the possibility of potential damage arable land in the Czech Republic, (Rusek 1967). This to agricultural crops. However, the abundance of Ela- may be due to the lower pH values of fertilized fields. teridae larvae in a regularly mown meadow (fallow II Parker & Howard (2001) reviewed that A. lineatus was at the start of observation) was an order of magnitude found more commonly than A. obscurus in plots with higher than in fallow I (Table 1), and thus the role of ahighpHintheU.K. fallow as a reservoir of Elateridae is lower compared to In agreement with other authors (Ghilyarov 1953; managed meadows. Contrary to fallow I, the abandon- Cherepanov 1965) tillage seems to be the main factor ment of termination of mowing fallow II plots resulted limiting the abundance of both dominant species and in a slight decrease in Elateridae abundance. consequently all Elateridae in arable land. Our results A total of six species of Elateridae larvae be- indicated that A. obscurus seems to be more sensitive longing to three trophic groups (Cherepanov 1965): to tillage than A. niger.ThesizeofA. obscurus larvae polyphagous A. obscurus; carnivorous and saprofagous found during the cultivation period corresponds to one- A. niger, A. subfuscus, A. vittatus and carnivorous D. year-old larvae (Ghilyarov 1953). This finding together marginatus and A. murinus were recorded in the study with the absence of A. obscurus larvae in the soil after plots. autumnal cultivation may indicate that A. obscurus lar- Agriotes obscurus and Athous niger were the most vae are strongly reduced or even eliminated by autum- abundant species in the plots, A. niger being most nal cultivation and the field population is reestablished abundant in the field and A. obscurus in other plots. each year by new colonizers from surrounding habitats. Vernon (1997, 2001) found A. obscurus abundant in The abundance of A. obscurus increased over time after 110 P. Jedlička & J. Frouz

field abandonment. The size of larvae also increased, the planation such as increasing predator pressure cannot largest larvae recorded in fallow where they may be able be excluded. to pupate (Ghilyarov 1953). No significant correlation Repeated findings of only small D. marginatus lar- was found between the presence of dominant species vae in fallow II indicate that there were optimal con- and soil moisture or temperature. This seems to be a ditions for female egg laying. However, due to the lack discrepancy with the findings that vertical migration of studies in ecology of this carnivorous species we can- and moulting of wireworms are strictly dependent on not clearly explain the reason for the absence of later seasonal changes of soil moisture and temperature (re- instars in our samples. viewed in Parker & Howard 2001). This could be caused by using data from a few years only and the fact that in these years massive vegetation changes occurred which Acknowledgements can hide seasonal periodicity or inter-seasonal variation This study was supported by Grant Agency of the Czech Re- caused by moisture and temperature. public (No. 526/97/0631) and research plan AV0Z60660521. In contrast to A. obscurus,larvaeofA. niger found We would like to thank Dr. K. Tajovský and Dr. V. Pižl in the field were heavier than the larvae of this species for collection of Coleoptera material for this study during found in remaining two plots (Fig. 4). The behavior their research. We thank Quick translation, M. Hanelova of the related species Athous heamorhoidalis (F., 1801) and Dr. A. Dear in particular for linguistic improvements. that belongs to the same ecological group as well as Two anonymous referees are thanked for their critical and Athous niger (polyphagous root eater and predator) helpful comments. was observed Hemerik et al. (2003). They demonstrated a higher mobility of A. haemorhoidalis in compari- References son with A. obscurus and pointed out its cannibalism, which might explain a more diffuse distribution of this Frouz J. 1994. Změny společenstev půdních dvoukřídlých (Dipte- species in their experiments. Hence a higher mobility ra) v průběhu sekundární sukcese na opuštěných polích. PhD and predatory or cannibalism activities of A. niger lar- Thesis, Academy of Sciences of the Czech Republic, České vae may be the cause of a higher portion of larger larvae Budějovice, Czech Republic, 199 pp. Frouz J. 1997. Changes in communities of soil dwelling dipteran in the field. larvae during secondary succession in abandoned fields. Eur. 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