© Entomologica Fennica. 16 September 201 1

The latitudinal uniformity of the unique life history of caprai (: ) and notes to the pre-overwintering period of selected water striders (Heteroptera: )

Tomas Ditrich, Miroslav Papaéek & Mikko Heino

Ditrich, T., Papacek, M. & Heino, M. 2011: The latitudinal uniformity of the unique life history of (Heteroptera: Veliidae) and notes to the pre- overwintering period ofselected water striders (Heteroptera: Gerridae). — Ento- mol. Fennica 22: 106—112.

Temperate water striders (Gerridae) overwinter as adults and die after spring re- production. European water cricket Velia caprai (Veliidae) overwinters concur- rently in egg and adult stage in Central Europe. This rare overwintering strategy goes with longevity ofthis . Adults can survive two winters in Central Eu- rope, unlike other semiaquatic bugs. Scandinavian populations of V. caprai and water striders lacustris and G. lateralis were examined at the beginning and end of September to determine their life histories. Both gerrids start to overwinter during September, females prior to males and macropterous individu- als prior to brachypterous. All females of G. lacustris and G. lateralis enter repro- ductive diapause before winter. V. caprai overwinters in both adult and egg stage in Norway, and can probably survive two winters. Central European and Scandi- navian populations of V. caprai share the same unusual way ofoverwintering and probably also the whole life history.

T. Ditrich, Faculty ofEducation, University ofSouth Bohemia, Jeronymova 10, 3 71 I5 Ceske' Budejovice, Czech Republic, and Faculty ofScience, University of South Bohemia, Branisovska 31, 3 70 05 Ceske' Budej'ovice, Czech Republic; E— mail: [email protected] M. Papacek, Faculty ofEducation, University ofSouth Bohemia, Jeronymova 10, 3 71 I5 Ceske' Budejovice, Czech Republic; E—mail.‘ [email protected] M. Heino, Department ofBiology, University ofBergen, PO Box 7803, N—5020 Bergen, Norway; E—mail.‘ [email protected] Received 2 September 2010, accepted 22 November 2010

1. Introduction 2008). As other semiaquatic bugs (Heteroptera: ), V caprai moves on a water sur- The water cricket Velia caprai caprai Tamanini, face and feeds on trapped into a water 1947 (hereafter used V caprai refers to this sub- surface film. However, this species has a unique species) colonizes small forest streams and pud- life history, quite different from other semi- dles in most European countries (Mielewczyk aquatic bugs. According to available data, all 1980, Aukema & Rieger 1995, Ditrich et al. temperate water striders (Gerridae) and other Eu- ENTOMOL. FENNICA Vol. 22 *9 Urinal/min? oflzfl’ history of Valid capmz' 107

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‘ wBER 15~

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Fig. 1. Monthly means of temperature in Bergen, Norway (BER) and Ceske Budéjovice, the Czech Republic (CB) for years 2000—2008. Data were obtained from Norwegian Meteorological institute (2009) for Bergen, Fiesiand (station 50500; 00°17’21’N. 501335?) and The Czech Hydrometeorologicai institute (2009) for Ceske Budejovice (ca 48°58’N, 14°28’E). ropean semiaquatic bugs overwinter exclusively from limited knowledge on life history of some as adults (Brinkhurst 1959, Wroblewski 1980, other species. Spence & Andersen 1994). The pondweed bug A question is whether populations of V. cu— Mesoveliufirrcom Mulsant & Rey, 1852 (Meso- pmi from different latitudes have equal life his— veliidae) is the exception, as it. overwinters exclu— tory strategy. Data from most surveys report this sively in the egg stage (Zimmennann 1984). The species as univoltine, hibernating as adult (Couli— second exception is the V. CBpVClL it. regularly anos at al. 2008), or partly bivoltine, hibernating overwinters in both egg and adult stage in the as adult (Mielewczyk 1980, Wroblewski 1980, South Bohemia, the Czech Republic (from 480 Savage 1989). Because the distribution of V. 37’ N to 49° 10’), as was recently shown by Di- capmi reaches far to North, Norwegian popula-— trich & Papacek (2009b). Moreover, adults of V. tions were checked ifthe bugs share the same life capmi can successfully overwinter two consecu~ history as in Central European populations. tive winters and thus exhibit extreme longevity Whereas climate in the Czech Republic is typi- (Ditrich & Papaicek 2009a). E.g., male adult, cally temperate continental (relatively warm marked and released in October 2007 in Novo- summers and cold winters), the climate in Bergen hradské Hory Mts. (the Czech Republic), was re— is northern oceanic (colder summers and mild captured alive in September 2009 (T. Ditrich, winters, Fig. l). Hypothetical uniformity of life unpubl.) Single specimen can thus survive three strategy within these different regions thus would succeeding winters __ first in the egg stage and indicate that the life history is shared by all popu— other two as adult. Such ability ofan individual to lations in Europe. For ensuring uniqueness of survive two seasons successfully is unusual presumed life history, also other common semi- among Gerromorpha. V. capmi thus exhibit aquatic bugs, present in the study area, were ex- unique life history in conditions of Central. Eun- amined. rope. However, the closely related V. sazriii prob- ably shares at least some life history traits (includ- ing overwintering strategy) with V. caprai (T. 2. aterial and ethods Ditrich & V. Kostal, in prep), but because know- ledge on life history of this species is too scarce, Populations from Bergen area (60015’N to 600 we consider the life history of V. cupmz' as 25’N) in Norway were chosen to compare life unique. We realize that this uniqueness results histories of semiaquatic bugs. All sites (see he—

ENTOMOL. FENNICA Vol. 22 ° Uniformity oflife history of Velia caprai 109

Table 1. Counts of collected adults, their sex and wing morph. MP: macropterous, BP: brachypterous, AP: apterous. First collecting period: 3rd—5th September, second collecting period: 25th—27th September.

First period Second period

Gerris lacustris 6 E2 6 E2 BP 88 ’l 30 52 43 M P 75 1 1 2 4 1 Gerris lateralis 6 E2 6 E2 AP 35 36 14 5 M P 5 2 2 0 Velia caprai 6 E2 6 E2 AP 1 1 1 160 123 202

their ovaries was classified according to Ditrich nymphs of G. lateralis and 2 and 2 nymphs of V. & Papacek (2009b): (i) immature (oocytes in caprai were found at the beginning and at the end germaria or oocytes and unovulated eggs present of September, respectively. Thus, only adults in the vitellaria), (ii) unreproductive mature were used for the analyses. The abundance of (chorionated eggs ovulated, “corpora lutea” visi- adults decreased significantly from the first to the ble, oviposition not detected), (iii) reproductive second collecting period in both water striders (X2 mature (oviposition detected by visible “corpus = 184.2, d.f.= 1,p<0.0001; 76:32.8, d.f.= 1,p< luteum” located caudally (distally) from the last 0.0001 for G. lacustris and G. lateralis, respec- egg within an ovariole). The overwintering of tively), but stayed unchanged in V. caprai (x2 = eggs should be indicated by presence of mature 2.01, d.f. =1,p = 0.16). females before winter.

Littoral and was searched floating vegetation 3.1. Sex ratio for eggs during the sampling. In addition, live specimens (at least 50 bugs of each species) were Results ofall samplings are summarized in Table transported to the South Bohemia and kept in 1. During the beginning of September, the sex ra- seminatural conditions (outdoor plastic boxes tio was significantly biased to females in G. with water and shore with moss and rocks) till lacustris and V. caprai (X2 = 15.4, d.f. = 1, p < November 2009, when the moss and rocks were 0.0001; x2 = 8.9, d.f. = 1, p = 0.003; respectively), searched for eggs. whereas it was balanced in G. lateralis (x2 = 0.05, d.f. = 1, p = 0.82). The situation changed at the end of when the sex ratio was bal- 2.3. Statistical analyses September, anced in G. lacustris (x2 = 1.4, d.f. = 1, p = 0.23), Sex ratios were compared to the balanced propor- male biased in G. lateralis (x2 = 5.8, d.f. = 1, p = tion (1:1) using X2 test in both collecting periods. 0.016) and stayed female biased in V. caprai (x2 = All other differences in sex ratios, wing morph 19.2, d.f. = 1,p < 0.0001). The difference in the proportions and collecting periods were com- sex ratio between the samples from particular pe- pared using X2 contingency tables. Sexual matu- riods was significant in G. lacustris and G. rity between periods was compared with the non- lateralis (contingency tables, X2 = 8.1, d.f. = 1, p = parametric Mann-Whitney test. The level of sig- 0.004; X2 = 4.2, d.f. = 1,]? = 0.04; respectively),

= nificance was set as OL 0.05 . All tests were run in but non-significant in V. caprai (contingency software package Statistica 8.0. tables, x2 = 0.6, d.f. = 1, p = 0.44).

3.2. Frequency of Wing morphs 3. Results Whereas both gerrids were found in two wing Adults were mostly found in both collecting peri- morphs (in G. lacustris macropterous and bra- ods. Only 4 and 1 nymphs of G. lacustris, 1 and 0 chypterous, MP and BP hereafter, respectively; 110 Ditrich et al. ° ENTOMOL. FENNICA Vol. 22

in G. lateralis MP and apterous, latter one AP Table 2. Sexual maturity in females of V caprai. of 30 selected found in hereafter), all individuals of V. caprai were Sample specimens Bergen area two periods in September 2009. apterous. Wing morph analyses were thus run for during collecting For dates of periods, see Table 1. gerrids only. The of was not sex frequency wing morphs Period Immature Mature dependent in any species in any sample from any collecting period (contingency tables, X2 = 0.003, Unrepro- Repro- d.f. = l,p= 0.96; x2 = 1.3, df. =1,p=0.26 for G. ductive ductive lacustrl's and G. laterall's in the sample from the First 23 1 6 first period; = 1.2, d.f. = 1,p = 0.27; = 0.7, X2 X2 Second 11 11 8 d.f. = 1, p = 0.4 for G. lacustris and G. lateralis in the sample from the second period). The wing morph data of the sexes were thus pooled. The wing morph frequency differed significantly be- during September. Individuals begun to prepare tween the samples from particular collecting peri- for the winter and number of active specimens of ods in G. lacustris. Whereas the frequency MP both species decreased. Females started to disap- morph almost equalled to that of BP morph dur- pear earlier/faster than males in both G. lacustrl's ing the first period, BP individuals dominated in and G. lateralis. Population of V. caprai stayed the samples from the second period (contingency unchanged with regard to the number of adults tables, x2 = 57.7, d.f. = 1, p < 0.0001, Table 1). No and the sex ratio. Both gerrids thus prepare for such pattern was found in G. lateralis, where overwintering earlier than V. caprai. As there was apterous specimens dominated in samples from not an apparent decrease oftemperature between both periods (contingency tables, X2 = 0.006, d.f. the collection periods, the preparation for over- = 1,p = 0.94, Table 1). wintering happens probably due to the change of the photoperiod rather than change in tempera- ture. of V. before win- 3.3. State of ovaries and oviposition Prolonged activity caprai ter is in accordance with rather active over- All examined females of G. lacustris and G. wintering of this species (Ditrich & Papacek lateralis were immature in both periods. State of 2009b). The female biased sex ratio in V caprai maturation in V. capraz' differed from that found in autumn populations is known from several Eu- in both gerrids. Part ofthe females was reproduc- ropean regions (Erlandsson 1993, Ditrich & tive in both periods. However, whereas most of Papacek 2009b). females were immature in the first period, propor- The population of the water strider G. lacus— tion of immature and unreproductive mature fe- Iris exhibited significant change in the frequency males equaled in the second collecting period of the wing morphs during the collecting periods (Table 2). The overall maturity of the examined in September. The macropterous individuals dis- females was significantly higher in the second pe- appeared earlier than the brachypterous ones. riod, compared to the first one (Mann-Whitney This phenomenon was found also in Great Britain test, U= 299,]? = 0.03). and Finland (Brinkhurst 1959, Vepsalainen No egg was found at any site during sampling 1974). According to Brinkhurst (1959), long in both periods. However, more than hundred winged individuals leave water and migrate to eggs of V. caprai were found in the moss in the overwintering sites earlier than the short winged outdoor box in November 2009. No egg was ones. Later, Andersen (1973) explained this fea- found in the boxes with gerrids. ture by the higher frequency ofbrachypterous in- dividuals among adults emerged in autumn. The results in the present study tend towards the first 4. Discussion explanation, because the wing morph frequency changed significantly in almost exclusively adult The Norwegian populations of G. lacustris and population. G. lateralis went through significant changes All examined females of both investigated ENTOMOL. FENNICA Vol. 22 ° Uniformity oflife history of Velia caprai 111 gerrids were immature during September, with- life history ofthis species in Britain should be re- out any progress in development of ovaries when examined. The overwintering strategy of V ca— comparing samples from the first and the second prai in Ireland has been studied by Murray & collecting period. These species thus overwinter Giller (1991) in detail. They claimed a non-dia- in reproductive diapause, reach sexual maturity pause overwintering, which was later confirmed and reproduce in spring, as commonly accepted in Central Europe (Ditrich & Papacek 2009b). for water striders (Spence & Andersen 1994). However, they did not record autumn or winter The presence of reproductive females of V. oviposition in their study and presumed over- caprai in samples from both collecting periods wintering in different stages ofadulthood and late can be explained by either (i) rapid sexual matu- nymphal instars. Murray & Giller (1991) also re- ration ofall females ofthe newly hatched summer port relative longevity of V caprai (male in No- generation, (ii) differently timed sexual matura- vember 1986 was recaptured in August, 1987). tion in differently aged time splitting cohorts of Nevertheless, the presence of mature females in one generation that is equally finished in Septem- all samples throughout year 1987 was ascribed to ber, or (iii) by longevity of the fully matured old overlapping generations rather than to continual overwintering generation. As adults of V. caprai survival of at least some individuals. We suppose can apparently survive two consequent winters in that the ability to overwinter two succeeding win- the Czech Republic (Ditrich & Papacek 2009a), ters is common to V caprai through Europe. and there was only one unreproductive mature fe- male present in samples from the first collecting period, the last explanation should be preferred 5. Conclusion for the Norwegian population. State of ovaries found in females of V. caprai in samples from Water striders start overwintering during Sep- both collecting periods indicates their maturation tember in Bergen area in Norway. Macropterous during the autumn and possible oviposition be- adults of G. lacustris leave water surface earlier fore winter. This phenomenon was confirmed by than brachypterous ones, as proposed by Brink- oviposition in November, detected in females hurst (1959). All gerrid females are immature from the Norwegian population reared in semi- when entering reproductive diapause prior to natural conditions. V caprai overwinters in both overwintering. The Scandinavian population of adult and egg stage in Norway. The possibility of V. caprai shares the life history with Central Eu- egg overwintering of V caprai, suggested by ropean populations — i.e., overwinters in both Cobben (1968) and Poisson (1924), is thus con- adult and egg stage and the adults can probably firmed in different populations. Overwintered survive two winters. The overwintering strategy adults in Norway can successfully survive proba- of this species, unknown among other semi- bly also second winter, assumed from the pres- aquatic bugs, does not show latitudinal variabil- ence of mature females at the beginning of Sep- ity. tember, which is similar to the situation from Central Europe (Papacek & Jandova 2003). Acknowledgements. 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