209

Hydrobiologia 324 : 209-217, 1996 . © 1996 Kluwer Academic Publishers . Printed in Belgium .

Distribution and associations of the aquatic Heteroptera of the Balearic Islands (Spain) J. Garcia-Aviles l , M. A. Puig 2

& A. G. Soler 3 1 Centro de Investigacidn de Espacios Naturales Protegidos, C/San Sebastian 71, 28791 Soto del Real (Madrid), Spain 2 Centre d' Estudis Avancats, Cam( Sta. Barbara s/n, 17300 Blanes (Gerona), Spain 3 Departamento de Biologla Animal y Ecologla, Facultad de Biologla, Universidad de Murcia, Campus de Espinardo, 30071 Murcia, Spain

Received 1 March 1995 ; in revised form 18 October 1995 ; accepted 6 December 1995

Key words : Heteroptera, distribution, associations, Balearic Islands

Abstract Twenty-five species of aquatic Heteroptera were collected from the Balearic Islands . Five are first records (Sigara nigrolineata, Micronecta scholtzi, Ranatra linearis, Notonecta meridionalis and Hebrus pusillus) . Previous records are also discussed . The spatial structure of the communities on the Islands is analysed . The different abundance of species and their characteristic habitats are identified . The species associations for each island are established through factorial analysis (correspondence analysis) ; a total of 8 associations are defined . They represent permanent habitats, with the exception of one, characteristic of seasonal ponds of Mallorca . Within the permanent lentic habitats, a clear difference occurs between artificial habitats ('albercas' : stone or cemented man-made irrigation ponds) and natural pond habitats .

Introduction

Material and methods

The Heteroptera of the Balearic Islands are relatively well known, with studies published since the last (Ramis, 1814 ; Bolfvar & Chicote, 1879 ; Moragues, 1894) as well as in the present century (Saunders, 1901 ; Royer, 1906 ; Garcfas, 1907 ; Torre, 1911 ; S'anchez, 1918 ; Eidmann, 1927 ; Villarrubia & Espanol, 1933 ; Espanol, 1935 ; Tamanini, 1948, 1949 ; Palau, 1949 ; Margalef, 1951, 1952, 1953 ; Bigot, 1958 ; Compte, 1960 ; Ribes, 1965, Compte, 1968 ; Tamanini, 1971 ; Ribes, 1977, 1978, 1984 ; Pons, 1987 ; Nieser & Montes, 1988) . Yet, most deal only with single islands and do not discuss habitat preferences . In this study, we provide a synoptic information and describe species associations and ecological preferences .

A total of 246 sites (120 in Mallorca, 68 in Menorca, 41 in Ibiza and 17 in Formentera) were sampled in winter (February and March 1988) and spring (May and June 1988) (Garcfa-Avilt s, 1990) using a 30 cm square net with 100 ,am mesh size . Figure 1 shows the geographical location of the Balearic Islands ; Table 1 provides a summary of the types of habitat of the sampling sites . Specimens were identified using the keys of Tamanini (1979), Jansson (1986), Poisson (1957), Macan (1976), Murillo (1985) and Milldn et al. (1987) . In order to define species associations, a multiple correspondence factorial analysis, version SPAD .N (Lebart et al ., 1987), was applied to each of the islands . In this analysis presence/absence data were used . Stations lacking Heteroptera were not eliminated from the analysis .



210 Table 1 . Location and characteristics of the sampling sites

Habitat

Sites

Stream

Pond

'Alberca'

Marsh Spring

Reservoir

Mallorca

Menorca

2, 3, 6, 7, 8, 9, 10, 11, 12, 14, 15, 26, 27, 28, 31, 34, 36, 37, 38, 39, 62, 63, 65, 66, 69, 72, 73, 81, 83, 84, 85, 86, 88, 90, 92, 94, 100, 103, 104, 105, 108, 109, 111, 112, 119. 4, 13, 17, 18, 19, 20, 21, 22, 23, 24, 25, 47, 48, 50, 52, 53, 54, 55, 57, 58, 61, 93, 116, 117 .

125, 138, 147, 158, 165, 174, 184, 121, 135, 152, 176,

16, 43, 51, 56, 59, 60, 67, 71, 77, 78, 79, 80, 89, 95, 96, 97, 99, 106, 110, 114, 120 . 29, 30, 35, 40, 41, 42, 44, 45, 46, 101 . 1, 5, 32, 33, 49, 64, 68, 70, 76, 82, 87, 91, 98, 102, 107, 113, 115, 118 . 74, 75 .

153, 166, 173, 188 .

126, 132, 139, 140, 148, 149, 159, 160, 167, 168, 175, 181, 186 . 122, 124, 141, 143, 154, 155, 178, 185 .

136, 142, 151, 161, 171, 182,

137, 145, 157, 164, 172, 183,

131, 134, 144, 150, 156, 162,

123, 127, 128, 129, 130, 133, 146, 169, 177 . 163, 170, 179, 180, 187 .

Ibiza

Formentera

190, 191, 208, 209, 213, 216, 223 .

237, 238, 239 .

201, 207, 229 .

234, 240, 241, 243, 244, 246 .

189, 200, 214, 220, 202,

242 .

192, 195, 196, 197, 203, 205, 210, 212, 215, 217, 218, 219, 221, 222 . 226 .

230, 231, 232, 235, 236, 245 . 233 .

193, 194, 198, 199, 204, 206, 211, 224, 225, 227, 228 .

Table 2. Definitions of Abundance of each

MENORC ;,

species on each island Abundance

Proportion of sites from which recorded

Very abundant IBIZA

(~

0

30 km

Abundant Common Scarce Rare Very rare

> 50% 30%-50% 15%-29% 5%-14%

<5% Only 1 site

FORMENTERA Figure 1 . Geographical location of the Balearic Islands

Based on the scores of the multiple correspondence analysis, a cluster of 20 fixed groups was formed for cases considered in each analysis . These were organized into five classes in order to maximize objectivity .

Species A total of 25 species were captured, five of wich (Sigara nigrolineata, Micronecta scholtzi, Ranatra linearis, Notonecta meridionalis and Hebrus pusillus) are first records for the Islands . The species, islands, recording sites, abundance on each island (Table 2),

preferred habitats, and other factors are mentioned below. Corixa affinis Leach, 1817 Mallorca: Scarce (sites : 17, 20, 22, 23, 55, 57, 58, 61) . Menorca : Abundant (sites : 121, 124, 126, 130, 131, 132, 134, 135, 137, 138, 140, 141, 147, 150, 154, 155, 156, 160, 161, 162, 172, 175, 176, 185, 186) . Ibiza : Very rare (site : 197) . In ponds and streams (with slow or almost no current), usually with aquatic vegetation and fresh or slightly brackish water .

21 1 Corixa panzeri (Fieber, 1848) Mallorca : Very rare (site : 89) . Menorca: Common (sites : 121, 124, 125, 131, 132, 135, 136, 137, 139, 140, 141, 154, 155, 175, 182, 183, 186) . First record for Mallorca . In ponds and streams (with slow or almost no current), always with aquatic vegetation and fresh or slightly brackish water. Parasigara perdubia (Rey, 1894) Mallorca: Scarce (sites : 9, 16, 81, 91, 104, 105) . Menorca : Scarce (sites : 137, 140, 159, 160, 161, 174, 183, 188) . First record for Mallorca . Mainly in streams with slow to moderate current, with or without vegetation and fresh water . Cited for Ibiza (Nieser & Montes, 1988) in a stream formed by the Broils d'es Bosquetell spring . During our study, this stream had completely dried up . Sigara lateralis (Leach, 1817) Mallorca : Scarce (sites : 17, 18, 19, 20, 23, 52, 53, 54, 55, 57, 58, 61, 79) . Menorca : Common (sites : 122, 123, 124, 129, 130, 135, 137, 138, 141, 147, 150, 154, 155, 156, 162, 175, 176, 182, 185) . Formentera : Rare (sites : 238, 239) . First record for Formentera . Mainly in ponds with or without vegetation and with fresh or brackish water . Sigara nigrolineata (Fieber, 1848) Mallorca : Rare (sites : 52, 109) . Ibiza : Scarce (sites : 192, 200, 217) . New for the fauna of the Balearic Islands . Mainly in lentic habitats, with or without vegetation and fresh water. In Ibiza always in 'albercas' (small man-made ponds for irrigation made of cement or stone walls) ; in Mallorca, in a pond and in a seasonal stream with almost no current . Sigara selecta (Fieber, 1848) Mallorca : Scarce (sites : 41, 42, 43, 44, 45, 48, 77) . Menorca: Very rare (site : 127) . Always in stagnant brackish waters, whether they are natural (marshes, coastal lagoons, etc .) or artificial ('albercas'), with or without vegetation . Cited by Ribes (1984) for Ibiza, based on records by Gasull in 1945, in an area long dried up or altered . Because of this and the lack of subsequent records, its current presence in Ibiza is in need of confirmation .

Sigara stagnalis (Leach, 1817) Menorca: Scarce (sites : 129, 130, 136, 139, 150, 176, 182, 185) . Always in lentic habitats (marshes, ponds and the mouths of streams), mainly in brackish water, with or without vegetation . Cited for Mallorca by Moragues (1894) and Bigot (1958) . Because of the destruction or disappearance of recording habitats and a lack of subsequent records since then, its current presence is in need of confirmation . Micronecta scholtzi (Fieber, 1860) Mallorca : Rare (sites : 74, 75, 117) . Ibiza : Scarce (sites: 192, 203, 210, 221, 222) . New for the fauna of the Balearic Islands. In great numbers in the Cuber and Gorg Blau reservoirs in Mallorca. In Ibiza, always in small numbers in 'albercas' with or without aquatic vegetation and fresh or slightly brackish water. Naucoris maculatus Fabricius, 1798 Mallorca: Rare (sites : 89, 90, 102) . Menorca : Rare (sites : 160, 174) . Always in permanent lentic habitats, with abundant aquatic vegetation and fresh or very slightly brackish water . Cited for Ibiza by Ribes (1984) and Nieser & Montes (1988) . Nepa cinerea Linnaeus, 1758 Mallorca : Scarce (sites : 9, 21, 22, 62, 63, 88, 102, 108, 115) . Menorca : Scarce (sites : 138, 139, 140, 151, 155, 161, 176, 184, 186, 187) . Ibiza: Very rare (site : 190) . First record for Ibiza . On banks of streams and ponds, usually in areas with vegetation and fresh or slightly brackish water . Ranatra linearis (Linnaeus, 1758) Menorca: Very rare (site : 174) . New for the fauna of the Balearic Islands . In the La Vall stream, near its mouth, in an area of permanent and fresh waters, with almost no current and abundant macrophytes . Anisops debilis perplexa Poisson, 1929 Mallorca : Rare (sites : 51, 80, 89, 105) . Ibiza : Scarce (sites : 203, 210, 215, 217, 219) . Formentera : Very rare (site : 242) . First record for Formentera .

2 12 Always in 'albercas', with or without vegetation and fresh or slightly brackish water. Anisops sardea Herrich-Schaffer, 1850 Mallorca : Scarce (sites : 19, 20, 51, 52, 80, 89, 114, 117) . Menorca : Abundant (sites : 121, 122, 123, 130, 131, 134, 135, 140, 141, 145, 147, 150, 154, 155, 156, 162, 166, 172, 176, 178, 182, 185, 186) . Ibiza : Rare (sites : 203, 217) . Mainly in ponds and 'albercas', with or without vegetation and fresh or brackish water. In Menorca, also in stream still-waters . Notonecta meridionalis Poisson, 1926 Menorca : Scarce (sites : 126, 141, 150, 156, 157, 176, 185) . New for Balearic Island fauna . In ponds and two streams with slow current ; always in areas with macrophytes and fresh or slightly brackish water. Notonecta maculata Fabricius, 1794 Mallorca : Common (sites : 2, 6, 9, 11, 12, 16, 17, 18, 19, 20, 31, 43, 51, 52, 56, 57, 60, 61, 63, 73, 80, 85, 88, 89, 91, 93, 97, 105, 106, 110, 114) . Menorca : Common (sites : 121, 126, 137, 140, 141, 147, 149, 150, 155, 160, 166, 172, 175, 178, 183, 184, 185, 186) . Ibiza : Common (sites : 189, 190, 192, 200, 203, 210, 215, 216, 218, 219) . Formentera : Very rare (site : 242) . First record for Formentera. In very diverse habitats (mainly 'albercas', ponds and stream still-waters), with or without vegetation and fresh or slightly brackish water . Several authors (Ribes, 1965 ; Nieser & Montes, 1988) regard notes of Notonecta glauca for Mallorca (Moragues, 1894 ; Garcias, 1907 ; Compte, 1960) as belonging to N. maculata . Notonecta viridis viridis Delcourt, 1909 Menorca : Scarce (sites : 121, 135, 137, 141, 150, 156, 157) . In ponds and stream still-waters with abundant aquatic vegetation and fresh or slightly brackish water . Plea minutissima Leach, 1817 Mallorca : Common (sites : 12, 16, 17, 18, 20, 21, 22, 47, 52, 53, 60, 81, 83, 89, 90, 93, 116, 117) . Menorca : Abundant (sites : 121, 131, 132, 134, 135, 136, 137, 139, 140, 141, 145, 146, 147, 150, 154, 155, 156, 160, 161, 162, 165, 167, 174, 175, 176, 182, 183, 186, 187, 188) . Ibiza : Scarce (sites : 190, 201, 203, 216, 220,

222) . Formentera : Very rare (site : 233) . First record for Formentera . In very diverse habitats (from streams to sources or marshes), always in lentic areas with abundant aquatic vegetation . Aquarius najas (De Geer, 1773) Mallorca: Scarce (sites : 2, 9, 81, 82, 91, 92) . Menorca : Rare (sites : 159, 160) . Always in permanent fresh waters (sources and streams) with or without vegetation and with or without current. Gerris argentatus Schummel, 1832 Menorca : Rare (sites : 160, 174) . In stream still-waters with abundant emerging macrophytes and fresh water . Gerris thoracicus Schummel, 1832 Mallorca : Rare (sites : 3, 16, 51, 55, 78) . Menorca : Common (sites : 126, 132, 135, 136, 137, 138, 140, 141, 147, 151, 155, 156, 158, 162, 175, 176, 182, 183, 185, 186) . In very diverse habitats (mainly in streams, ponds and 'albercas') with fresh and brackish water and aquatic vegetation . Hebrus pusillus (Fallen, 1807) Mallorca : Very rare (site : 102). New for the fauna of the Balearic Islands . In the Estany de la Fuente de Sant Joan, a small lagoon with a coverage of the alga Enteromorpha intestinales in pleustonic form (Martinez Taberner, 1988) and abundant emerging riparian vegetation . Hydrometra stagnorum (Linnaeus, 1758) Mallorca : Common (sites : 2, 3, 7, 10, 12, 21, 22, 62, 63, 72, 73, 81, 83, 86, 88, 91, 106, 120) . Menorca : Common (sites : 132, 137, 138, 140, 142, 155, 157, 161, 172, 175, 178, 179, 183, 184, 185, 186, 187) . Ibiza : Scarce (sites : 190, 194, 201, 204, 223, 224) . On the banks of permanent aquatic habitats with or without vegetation and fresh or very slightly brackish waters . Mainly in streams on Mallorca and Menorca and in springs on Ibiza . Mesovelia vittigera Horvath, 1895 Mallorca : Rare (sites : 47, 90, 102, 114, 117) . Menorca : Scarce (sites : 132, 155, 175, 176, 182) . Ibiza : Very rare



213 (site : 208) . Formentera : Rare (sites : 233, 246) . First record for Ibiza and Formentera . Mainly in permanent fresh water habitats (large ponds, and still-waters and mouths of streams) with emerging vegetation .

C. affinis

OS. lateralis

S. nigrolineata •

• A. sardea

S. selecta M. scholtzi •

Microvelia pygmaea (Dufour, 1833) Mallorca : Scarce (sites : 21, 47, 60, 61, 81, 88, 89, 93, 97, 117, 120) . Menorca : Common (sites : 140, 147, 150, 151, 163, 165, 166, 176, 178, 186, 188) . Ibiza : Abundant (sites : 190, 191, 192, 193, 194, 197, 201, 204, 207, 216, 222, 223, 224, 229) . In stagnant waters and those of little current, mainly in areas with emerging or floating vegetation and fresh water.

+ 1 .5

•

I

G . thoracicus .4 M vittigera

+0 .6

• • • N. maculates P . minutissima • C panzeri N. maculatus A . debilis perplexes V hoberlandti M. pygmaea • H. pusilius _-1 .0 2

H. stagnorum • II N. cinerea •A . najas P. perdubia

••

Figure 2 . Plot of the first two axes of the multiple correspondence

Velia hoberlandti Tamanini, 1949 Mallorca : Scarce (sites : 1, 5, 6, 7, 9, 27, 34, 62, 67, 68, 69, 71, 82, 104, 105, 107) . Menorca : Scarce (sites : 141, 142, 163, 183, 187) . Endemic species of the Balearic Islands . In permanent habitats (springs and stream stillwaters), usually with fresh water and with or without vegetation . Records of V rivulorum for the Balearic Islands antidate to the description of V hoberlandti (Tamanini, 1949), and presumably belong to V hoberlandti . Notes of V caprai caprai by Ribes (1965) and Pons (1987) for Mallorca and Menorca are based on external taxonomical characters, and probably belong to V hoberlandti . Notes of V caprai caprai by Nieser & Montes (1988) for Mallorca and Menorca are identification errors and belong to V hoberlandti (Nieser, in litt.) . Hence, the only species of Velia present on the Islands is V hoberlandti .

analysis for the Heteroptera of Mallorca .

Associations of species

Figure 3 . Ordination of the sampling sites on Mallorca on the first

MALLORCA

two axes of the multiple correspondence analysis . The symbols used for each of the habitat types are : A springs, 0 streams, • 'albercas', 0 ponds, + marshes, 0 reservoirs .

Heteroptera were present in 77 of the 120 sampled sites on Mallorca, totalling 20 species . The first two axes of the correspondence analysis account for 14.94% and 11 .77% of the total variance, respectively . Axis 1 is defined by Sigara selecta at its positive end and by Anisops sardea, Mesovelia vittigera, Corixa panzeri, Naucoris maculatus and Anisops debilis perplexa at its negative end (Figure 2) . Axis

0

0

0

0 O E

--0 .60

11 A

A~ II

2 is associated at its positive end with Corixa affinis and Sigara lateralis and with Hydrometra stagnorum, Nepa cinerea, Parasigara perdubia and Aquarius najas at its negative end (Figure 2) . The distribution of sampling sites (Figure 3) shows almost all ponds in the upper left quadrant (-/+) and all marshes at the positive end of Axis 1 . Axis 2 separates lentic ecosystems (in particular temporal ponds



214 MALLORCA

r1,

CLASS 2 CLASS 3 CLASS 4 CLASS5

G . argenratus N. maculatus A . najas • • P. • R . linearis +2.25

pcrduh;a

q -- 7 101

i22, 13 C 1617 9~ 20

1

1

MENORCA

I CLASS 1 C CLASS 2[

3 5

1

I

7 CLASS 3 [ t0 r z 13 14 CLASS 4

P. minutissima • • N macalara affinis H. stagnonmr •C . panzeri obertaidti e• a • •C I • •N. viridis M. pygmaea •+ 1 .0 G. thoracicus vittigera A . sardea • -0 .25 S. lateralis • •N. meridionalis II •s stagnalis

16

n 1a

CLASS 5

C Zp 1

'1.

Figure 4. Dendrograms based on the scores of multiple correspondence analyses .

• S . selecta

Figure 5. Plot of the first two axes of the multiple correspondence analysis for the Heteroptera of Menorca .

at its positive end) from lotic habitats (in particular spring and permanent streams at its negative end) . On the whole, the negative and positive ends of Axis 1 are defined by species characteristic of permanent lentic fresh water ecosystems and of permanent lentic ecosystems with brackish waters, respectively . The positive and negative ends of Axis 2 are defined by species characteristic of temporal lentic ecosystems and of permanent lotic ecosystems, respectively . Remaining axes are associated only with stations with one species present, and cannot be defined . A cluster analysis was made based on the resulting scores of the preceding factorial analysis (Figure 4) and groups obtained were divided into five classes (Table 3) . Class 1 corresponds to sites which lacked species distinctive of the remaining groups and where only accidental species were present (Table 3) . In general, the following associations can be defined for Mallorca : 1 . Permanent lotic habitats (springs and streams) : Class 2 with Aquarius najas and Parasigara perdubia as the characteristic species . 2 . Seasonal lentic habitats (ponds and `albercas' ) . Class 3 with Sigara lateralis, Corixa affinis and Plea minutissima . 3 . Permanent 'albercas' . Class 4 with Anisops debilis perplexa, Anisops sardea and Notonecta maculata . 4 . Permanent ponds . Class 5 with Mesovelia vittigera, Micronecta scholtzi and Naucoris maculatus .

0 0

0

+0 .6

0

F71

n

0

- 0 .3 1

Aj

OD

A

r'0+

On o , 0

A

**0

00

0~

0

0 .2

00

0 O O O DO

0 .~~ 0 1

0

11

Figure 6 . Ordination of the sampling sites on Menorca on the first two axes of the multiple correspondence analysis . The symbols used for each of the habitat types are : A springs, O streams, • 'albercas', O ponds, * marshes .

MENORCA Heteroptera were present in 53 of the 68 sampled sites on Menorca, totalling 21 species . The first two axes of the multiple correspondence factorial analysis account for 21 .81% and 15 .65% of the total variance, respectively . Figure 5 shows the species associated with both axes . These are Notonecta viridis viridis, Mesovelia vittigera and Notonecta



2 15 Table 3 . Associations of characteristic species resulting from the classification (centroid) in classes, obtained with the scores defined in the correspondence factorial analysis . Classes cited as `without defined association' include those sites without the common species that are characteristic of the associations, but which contain accidental species instead . Island

Class Groups

Sites

Association

Mallorca

1

1, 2, 3, 4, 5, 6, 7.

Without defined association

2 3

8, 9 . 10, 11, 12, 13, 14.

4

15, 16.

1, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 21, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 48, 49, 50, 56, 59, 60, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 76, 77, 78, 83, 84, 85, 86, 87, 8 8, 93, 94, 95, 96, 97, 98, 99, 100, 101, 103, 104, 106, 107, 108, 109, 110, 111, 112 , 113, 115, 116, 118, 119, 120 . 2, 9, 81, 82, 91, 92. 16, 17, 18, 19, 20, 22, 23, 52, 53, 54, 55, 57, 58, 61, 79. 51, 80, 89, 105 .

5

17, 18, 19, 20.

47, 74, 75, 90, 102, 114, 117 .

1

1, 2, 3, 4 .

121, 126, 135, 137, 141, 150, 156, 157, 185 .

2 3

5, 6, 7 . 8, 9, 10, 11, 12 .

4

13, 14, 15, 16, 17, 18 .

5

19, 20 .

132, 138, 184, 122, 134, 153, 169, 160,

Menorca

155, 175, 176, 182 . 140, 142, 147, 151, 161, 163, 172, 178, 186, 187 . 123, 124, 125, 127, 128, 129, 130, 131, 136, 139, 143, 144, 145, 146, -148, 149, 154, 158, 159, 162, 164, 165, 166, 167, 170, 171, 173, 177, 179, 180, 181, 188 . 174.

meridionalis at the positive end of Axis 1 and Sigara selecta at the negative end . The positive end of Axis 2 is defined by Parasigara perdubia, Naucoris maculatus, Gerris argentatus, Ranatra linearis and Aquarius najas . Distribution of stations related to both axes (Figure 6) show most ponds in the lower right quadrant (+/-) and marshes and springs in the lower left quadrant On the whole, Axis 1 is associated with species characteristic of permanent fresh water lentic habitats on its positive end . Axis 2 separates species characteristic of permanent streams (at its positive end) from the remaining habitats . A cluster analysis based on the resulting axes of the correspondence analysis (Figure 4), established five site classes (Table 3), and their associated species . Class 4, with only accidental species, is characterized by the absence of species that define the rest. As a whole the following associations can be defined for Menorca : 1 . Permanent lentic habitats . a) In general : Class 1 with Notonecta viridis viridis, Notonecta meridionalis and Corixa affinis . b) Lentic habitats with

183, 133, 152, 168,

A . najas, P perdubia S. lateralis, C. affinis, P minutissima A . debilis perplexa, A, sardea, N. maculata M. vittigera, M. scholtzi, N. maculatus N. viridis viridis, N . meridionalis, C. affinis M. vittigera, G . thoracicus H. stagnorum, N. cinerea, V hoberlandti, M. pygmaea Without defined association

G. argentatus, N. maculatus, P perdubia

a clay substratum on the north coast : Class 2 with Mesovelia vittigera and Gerris thoracicus . 2 . Permanent streams . a) In general : Class 3 with Hydrometra stagnorum, Nepa cinerea, Velia hoberlandti and Microvelia pygmaea. b) Large still-waters : Class 5 with Gerris argentatus, Naucoris maculatus and Parasigara perdubia . IBIZA Heteroptera were present in 25 of the 41 sampled sites on Ibiza, totalling . l l species . Only Microvelia pygmaea and Notonecta maculata have been captured in over 25% of the sampled sites, whilst the remaining species con only be found in very few stations . The first two axes of the correspondence analysis account for 22 .45% and 19 .11% of the total variance, respectively . Axis 1 is defined by Anisops sardea, Anisops debilis perplexa, Sigara nigrolineata, Micronecta scholtzi and Notonecta maculata at its positive end, and by Corixa affinis and Hydrometra stagnorum at its negative end . Axis 2 is associated at its positive end with Nepa cinerea and Plea minutissi-

216 ma, and at its negative end with Mesovelia vittigera . Because of the small number of species and stations where they were found, there is no graphical representation of this analysis . The cluster does not define species associations but rather divides stations according to the presence or absence of the two most abundant species on the island (Microvelia pygmaea and Notonecta maculata) . Notonecta maculata was found mainly in artificial lentic habitats ('albercas') and Microvelia pygmaea in natural lentic habitats (ponds and stream pools) . FORMENTERA Heteroptera were present in 5 of the 17 sampled sites on Formentera, totalling 5 species . Sigara lateralis was found in two pools of a seasonal streams ; Anisops debilis perplexa and Notonecta maculata in an `alberca' ; Plea minutissima in a permanent pond and Mesovelia vittigera in this and another pond .

Conclusions A total of 25 species were collected . Five (Sigara nigrolineata, Micronecta scholtzi, Ranatra linearis, Notonecta meridionalis and Hebrus pusillus) are first records for the Balearic Islands . Only two of all previously cited species have not been found in our study . Sigara scripta, cited by Moragues (1894) for Mallorca in a long dried-up site, and Micronecta leucophala, cited by Tamanini (1948) for Mallorca based on specimens belonging to the Civic Natural History Museum of Genova and collected by Jorda, probably before 1930 . Due to the dates of these recordings and the lack of subsequent ones, the presence of both species on the Islands is in need of confirmation . With the exception of the endemic Velia hoberlandti, the remaining species are widely distributed throughout the Mediterranean area, particularly in the west . Only Anisops debilis perplexa has a smaller distribution area ; in the south of the Iberian Peninsula and the north of Africa (Nieser & Montes, 1984) . For the Balearic Islands, only permanent habitats show definite species associations, with the exception of Mallorca which has its own association of seasonal ponds (especially those situated in the area named Marinade Llucmajor) which is formed by Sigara lateralis, Corixa affinis and Plea minutissima .

Permanent lotic habitats are found only on Mallorca and Menorca . Associated with these habitats in Mallorca are Aquarius najas and Parasigara perdubia . In Menorca, Gerris argentatus, Naucoris maculatus and Parasigara perdubia are associated with the larger streams, while Hydrometra stagnorum, Nepa cinerea, Velia hoberlandti and Microvelia pygmaea are associated with the smaller streams with little current and abundant vegetation . As far as the permanent lentic habitats are concerned, there are obvious differences between the 'albercas' and the ponds . In the permanent 'albercas', wich are considerable both in number and extension in Mallorca and in Ibiza particularly (where they form the majority of permanent aquatic habitats) there is an association made up of Anisops debilis perplexa, Anisops sardea and Notonecta maculata . Menorca, with fewer 'albercas', has no definite species association for this habitat . With regard to permanent ponds, in Mallorca one can find an association composed of Mesovelia vittigera as characteristic species and Micronecta scholtzi and Naucoris maculatus as associated species . While in Menorca there are two associations, one including the majority of permanent ponds and which is made up by Notonecta viridis and Notonecta meridionalis as characteristic species and with Corixa affinis as associated species, and another association which is restricted to ponds with a clay substratum found on the north coast of the island and made up by Mesovelia vittigera as characteristic species and Gerris thoracicus as associated species .

Acknowledgements We thank Dr J . A . Palazon and Dr J . F. Calvo Sendin for help with statistical methods ; Dr N . Nieser and Dr A . Millan for help with taxonomical questions, and J . Larkin for revision of English manuscript .

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