Habitat selection in rock pool corixids: the effect of local density on dispersal

The corixid species breeding in temporary rock pools of Baltic archipelago live in a highly fragmented and unpredictable habitat. Shallow rock pools can dry out and be refilled repeatedly during a summer causing high mortality of immatures. In deeper pools, young nymphs face intense competition by older stages including cannibalism. The adult corixids move frequently between rock pools and are thus able to use currently available habitat for reproduction. In this dispersal behaviour, the ability to assess the local population density and hence select the more suitable low density patches would be advantageous. We studied the effect of local population density on the frequency of dispersive flights of Arctocorisa carinata (Sahlberg) and Callicorixa producta (Reuter) experimentally, using rock pools from which nymphs of both species were removed. The dispersal rates of marked C. producta adults were significantly lower from experimental rock pools than from normal density controls, leading to a concentration of C. producta adults in the experimental rock pools. Indications of immigration rate differences between the experimental and control pools were also observed. No clear differences were found in the superior competitor A. carinata.     

Preferred egg laying sites in Palmacorixa nana (Heteroptera : Corixidae)

Female Palmacorixa nana showed clear preference for wood oviposition substrates over Elodea and plexiglass in both laboratory and field experiments. Wood was chosen because of its rigidity and rough surface. These data raise the possibility that males could gain access to females by controlling localized resources.Present address: Department 0f Entomology University 0f Alberta Edmonton, Alberta, Canada T6 G 2E3Present address: Department 0f Entomology University 0f Alberta Edmonton, Alberta, Canada T6 G 2E3     

Tarsal asymmetry, nutritional condition, and survival in water boatmen (Callicorixa Vulnerata)

Fluctuating asymmetry (FA) has been used as a measure of developmental stability and may indicate individual phenotypic or genotypic quality. Using water boatmen (Callicorixa vulnerata) from a natural population, we examined the relationship between tarsal FA (tarsal spine number, tarsal length) and indices of body condition in two habitats. We used body weight and residual body weight (controlling for body length) as indices of condition because experimental food deprivation in water boatmen led to a reduction in each. We detected a negative relationship between FA and both indices of condition in two ecologically distinct pond habitats. We predicted this association was due to a negative relationship between FA and competitive feeding ability. Consequently, we examined associations between survival time and tarsal FA in C. vulnerata under resource-limited laboratory conditions. Univariate analyses revealed a negative correlation between survival and tarsal FA in each trait. Inclusion of survival time, body length, gender, tarsal spine number, tarsal length, and measures of FA into multivariate analyses revealed a negative correlation between survival and FA. Individuals with the greatest survival had higher nutritional condition than individuals that succumbed early in the experiment. Asymmetric individuals may suffer a foraging handicap as a result of the use of tarsi in feeding or they may be of poor genetic quality. Our results suggest elevated FA may limit resource acquisition and are consistent with the use of FA as a measure of fitness.     

Opposing selection on a sexually dimorphic trait through female choice and male competition in a water boatman

Female choice and male-male competition are traditionally considered to act in concert, with male competition facilitating female choice. This situation would enforce the strength of directional selection, which could reduce genetic variation and thus the benefits of choice. Here I show that in a water boatman, Sigara falleni, the direction of selection through female choice and male competition vary among traits under laboratory conditions. The two forces were mutually enforcive in acting on body size but exerted opposing selection on a sexually selected trait, male foreleg pala size. Female choice favored large palae, whereas male competition favored smaller palae, suggesting that large palae are costly in competition. This conflicting selection through female choice and male competition could be one of the forces that contribute to the maintenance of genetic variation in sexually selected traits.     

Two New Species of Tupiperla (Plecoptera: Gripopterygidae) from the Missions Area of Argentina and Paraguay

Tupiperla flinti sp. n. from Misiones in Argentina and from southern Paraguay, and T. misionera sp. n. from Misiones are described.     

A Chromosomal Investigation of the West European Species of <Emphasis Type="BoldItalic">Corixa</Emphasis> Geoffroy (Heteroptera: Corixidae)

C-banded karyotypes are provided for the five west European species of Corixa Geoffroy. All have 2n = 22 autosomes + sex chromosomes which are XY (♂), XX (♀). Some specimens of C. punctata have a small B-chromosome, while some C. panzeri have a fairly large one. The karyotypes of C. punctata, C. dentipes, C. affinis and C. panzeri are all distinctive, but the karyotypes of C. punctata and C. iberica appear indistinguishable. The Scottish material of C. punctata and C. iberica used in this study shows morphological intergradation between the two, suggesting that they hybridise where their ranges overlap. Meiosis shows very fine even pachytene bands in C. punctata, and that the autosomes form true bivalents during diplotene in C. affinis and C. panzeri, while the sex chromosomes appear closely associated. At first metaphase the sex chromosomes may appear either closely associated or may have separated. There is no evidence of the presence of m-chromosomes.     

The Gammaridae and Corixidae of an inland saline lake from 1975 to 1978

When observations began the population of Watch Lane Flash consisted of Gammarus duebeni and Sigara lateralis. Gammarus tigrinus was then introduced; probably during a transfer of water from a nearby canal. G. tigrinus rapidly increased in numbers and at the same time G. duebeni and S. lateralis decreased to zero. There followed a partial recolonisation by corixids but the species present were Sigara concinna and Sigara dorsalis. Throughout the study period corixid populations were stable in two immediately adjacent water bodies, one of which also contained G. duebeni. Thus the changes described were associated with the presence of G. tigrinus. The reasons for the success of G. tigrinus and its effects on other gammarids and corixids are discussed.     

The ecology of the Corixidae (Hemiptera: Heteroptera) in the Corrib catchment,Ireland

Two surveys were carried out in the Corrib catchment (Ireland) to determine the physical and chemical factors that govern the distribution of Corixidae. Of the twenty one species recorded, five species, Sigara scotti (Fieber), S. distincta (Fieber), S. fossarum (Leach), S. fallenoidea (Hungerford) and Cymatia bonsdorffii (Sahlberg) comprised 82% of the numerical total. Although individual species occurred in chemically diverse sites species assemblages and changes in the relative abundance of the majority of species and in species richness and diversity were evident in the progression from hard to soft water. High altitude soft water sites had a much lower number of species compared with chemically similar low altitude sites. In Lough Corrib, the main body of water in the catchment, most species were abundant only in sheltered areas with mud substrates and high percentage vegetation cover. Species diversity was high in these areas and either C. bonsdorffii, S. fossarum, S. fallenoidea or Callicorixa praeusta (Fieber) dominated numerically. However, S. scotti, S. dorsalis (Leach) and Arctocorisa germari (Fieber) were more abundant in exposed areas with sand, gravel or mearl substrates. In temporary ponds and in lotic water species diversity was also high but species composition (mainly C. praeusta, Sigara nigrolineata (Fieber), Corixa punctata (Illiger), C. panzeri (Fieber), C. bonsdorffii) was different to that of temporally stable lentic habitats.     

Competitive interactions limiting the number of species in rock pools: experiments with Sigara nigrolineata

Rock-pool corixids (Hemiptera) Arctocorisa carinata and Callicorixa producta were excluded from small rock pools. First-stage larvae of Sigara nigrolineata, separately or together with larvae of either of the rock-pool species, were then introduced daily at a rate simulating reproduction by typical populations. In all three treatments, the survival of S. nigrolineata larvae was high at the beginning of experiment, 0.39–0.83 between the 1st and 5th stages, but later high mortality was observed. C. producta adults tended to invade experimental rock pools and towards the end of the experiment larvae of this species were dominant. Oviposition rates and developmental rates of the three species are comparable. In laboratory tests, young larvae of S. nigrolineata were more vulnerable to interspecific predation than those of the rock-pool species, and older larvae proved to be less efficient predators. In rock pools, there are no environmental factors preventing successful reproduction by S. nigrolineata. However, competition and predation by the two other rock-pool species seem to prevent successful reproduction. Dispersal in S. nigrolineata is too slow for efficient colonization of rapidly changing rock-pool environments.     

Patterns in attachment sites of the parasite Hydrachna guanajuatensis Cook, 1980 (Acari: Hydrachnidiae) on aquatic heteropterans (Nepomorpha) from the Tecocomulco Lake,Mexico

The water mite Hydrachna guanajuatensis Cook, 1980 Cook, D. (1980), ‘Studies on Neotropical Water Mites’ Memoirs of the American Entomological Institute, 31, 1–645. [Google Scholar] is recorded as an ectoparasite of Ranatra sp. (Nepidae), Notonecta sp., Buenoa sp. (Notonectidae), Krizousacorixa femorata (Guérin, 1857), Trichocorixella mexicana (Hungerford, 1927), and Hesperocorixa laevigata (Uhler, 1893) (Corixidae). The host body region, where the larvae and protonymph attach, depends significantly on the heteropteran species: χ² = 3969.43, p < 0.05 and χ² = 1893.6, p < 0.05, respectively. We performed a cross tabulation with a correspondence analysis and found three associations for the larvae: 1) dorsal side of abdomen underneath the wings of the two species of Notonectidae, 2) head, wings, and hind legs of two of the species of Corixidae (T. mexicana and K. femorata), and 3) thorax and fore and middle legs of the single species of Nepidae. These different patterns are discussed according to morphological and ecological characteristics of the hosts. This is the first study that deals with the spatial distribution patterns within the same species of ectoparasite.