Two calanoids,two lakes,and a decade or two. An updated record and evaluation of occurrence and periodicity of Tropodiaptomus spectabilis and Metadiaptomus meridianus (Copepoda: Calanoida), and alternative stable states in two cascading impoundments

Episodic switching between Tropodiaptomus spectabilis and Metadiaptomus meridianus in L. Midmar (29° 30 S, 30° 12 E), and transitory seasonal alternation of these taxa in L. Albert Falls (29° 26 S, 30° 26 E) recorded in comparative studies of these inter-leading reservoirs between 1989 and 1999, along with historical records for Midmar extending back to 1978, are updated and re-evaluated in light of subsequent and additional findings. In the longer term, an `exclusive' occupancy by one or another species has been maintained in these and other inter-leading impoundments on the quasi-subtropical Mgeni River. Sympatry was invariably transitional. It lasted several months in the upper Midmar system, and where protracted over several years as in the downstream Albert Falls system, was effectively negated by seasonal separation of the taxa. Possible influences of parasitism, changes in water turbidity or pH, dependent or independent of inter-basin water transfers, and such water transfers themselves, are explored and rejected as proximate causes of species replacement. Because evidence for the existence of resting eggs was contradictory (respectively present and absent in preserved and live samples), emergence from diapause is considered an unlikely source of re-colonisation. The guild complement of invertebrate planktivores is comparable in both lakes, seemingly removing predation as a determinant factor. The comparability of food thresholds for various measures of demographic performance suggests remarkable similarity in the competitive potential of these species, which additionally show considerable niche overlap in terms of adult diet, and comparable vulnerability to ellobiopsid parasitism. Ecological separation is thus limited to differentiation of thermal optima, functional feeding biology of juvenile stages – especially nauplii, and sediment tolerance. Evidence now available supports previous arguments that species separations remain attributable largely to marginal species differences in thermal optima, mirrored in the pattern of seasonal separation during an episode of sympatry (1990 to early 1994) in the down-stream Albert Falls system. While no causal explanation can be substantiated from evidence gleaned during this decade of study, the species replacements observed in Midmar appear to reflect alternative stable states, induced by presently unknown factor(s), plausibly temperature, or improbably, human translocation. By contrast, alternative stable states are not manifest in Albert Falls, wherein the longer term, T. spectabilis seemingly represents the only stable state, a feature apparently shared by other warmer reservoirs down the Mgeni cascade. The unpredictability of chaotic dynamics precludes its analysis in this situation, while conversely, the system provides a unique model for meta-population analysis, related to uni-directionality of natural dispersal. However, the cost-effectiveness of continued monitoring for unforeseeable events poses a serious practical dilemma.     

ASPECTS OF COMPARATIVE PLANKTON ECOLOGY IN CASCADING MGENI RIVER RESERVOIRS (MIDMAR,ALBERT FALLS,AND NAGLE): AN OVERVIEW

Summary

An overview of a three year study of abundance, community structure and succession of zooplankton and phytoplankton in relation to physical limnological conditions in Lakes Midmar and Albert Falls is presented, along with findings on zooplankton from a nine month study of Lake Nagle. Physical stability increased between Midmar (mean summer N² = 6.55 × 10⁴ s²) and Albert Falls (N² = 8.70 × 10⁴ s²), in line with elevations in water temperature. Phytoplankton richness and diversity was similar in these reservoirs, although zooplankton species richness increased downstream. Abundance levels of both phyto- and zoo-plankton were broadly comparable in these two reservoirs. In Midmar and Albert Falls, overall mean (± SD) chlorophyll levels were 3.60 ± 1.54 and 3.41 ± 1.41 μg 1¹, with corresponding overall average zooplankton standing stocks of 0.85 and 0.76 g m² dry mass, dropping to 0.54 g m² in Nagle (for which spring to midsummer data are missing).

Ruderal and colonist phytoplankters were persistently dominant both in Midmar and Albert Falls, in keeping with the continuous (if incomplete) mixing patterns evident in these reservoirs. Few stress tolerant algae occurred. The summer ruderal assemblage was unexpectedly dominated by diatoms in the physically more stable conditions of Albert Falls, but not Midmar. Mean zooplankton grazer-induced instantaneous mortality rates for planktonic algae for the whole study were estimated (by regression predictions) as 0.17 d¹ in both lakes. Phytoplankton was not studied in Nagle.

Changes in zooplankton community structure between Midmar and Nagle largely involved progressive increases in the contribution of smaller-bodied cladocerans (comprising both sequentially smaller species of Daphnia (D. pulex, D. longispina, D. laevis), and additional genera such as Diaphanosoma, Ceriodapnia, Moina and Bosmina). As with a parallel progressive switch between Metadiaptomus meridianus and Tropodiaptomus spectabilis over this series of reservoirs, (and the temporal separation of “co-existing” populations in Albert Falls), which has been shown experimentally to be strongly temperature-linked, changes in absolute temperature are implicated as a primary causal factor in the shifts in cladoceran species composition. Temporal occurrences of these species also indicate the primacy of temperature.     

Food and suspended sediment influences on the naupliar and copepodid durations of freshwater copepods: comparative studies on Tropodiaptomus and Metadiaptomus

Post-embryonic durations of Tropodiaptomus spectabilis (Kiefer)and Metadiaptomus colonialis(van Douwe) were determined at 20°Cin laboratory factorial experiments involving four algal foodenrichment levels (0, 100, 500 and 2500 µg l^–1 Cof Selenastrum added to 20 µm filtered water from respectivesource-lakes) and three suspended sediment levels (filtered,natural, and 2- to 3-fold sediment-enriched lake water). Foodeffects (30, 75, 225 and 600 (µg ^–1 C of Scenedesmus)were tested alone at 20°C for Metadiaptomus meridianus (vanDouwe). Total naupliar (D_n) and total copepodid (D_c) developmenttimes [summed to give total post-embryonic duration (D_t)] andmetasome lengths at maturity were measured In all taxa, foodsupply maximally affected D_c values 2- to 3-fold, whereas itsmaximal influence on D_n values was relatively slight (generally25%). The measured effect of food supply on D_t, was as strongas the predicted influence of temperature over an appropriateannual range. Food supply influenced size at maturity, and probablythereby fecundity, thus exerting additional demographic influences.Sediment effects were inconsistent, and quantitatively weakerthan food effects Total development of T.spectabilis was 20%raster, and that of M.colonialis 15% slower in sediment-enrichedthan in natural sediment level treatments; contrasting baselinesediment levels (2–3 times higher for the latter species)and different enrichment procedures confound interpretation.Unexpectedly, and inexplicably, development almost invariablyfailed in sediment-free water, implying an apparent dependencyon inorganic particles in these taxa This contrasts with thegenerally adverse influences of high sediment concentrationsupon zooplankton. Minimal male and female D_t values at 20°Cwere comparable and significantly longer in M.colonialis (15.5and 17 7 days) and M meridianus (16.5 and 21.5 days) than inT.spectabilis (11.7 and 12 2 days). These differences in durationare ecologically incongruous in relation to expected r –K life history strategies of genera characteristic of temporaryor semipermanent waters and permanent waters respectively.     

Nutritional suitability of some uni-algal diets for freshwater calanoids: unexpected inadequacies of commonly used edible greens and others

• 1 Naupliar and copepodid development times (Dn and Dc, respectively) of two African freshwater calanoids (Metadiaptomus meridianus and Tropodiaptomus spectabilis) were measured on mono-specific diets of comparably sized Chlamydomonas reinhardii, Scenedesmus acutus, Cryptomonas sp., Rhodomonas minuta, Cyclotella meneghiniana, and Selenastrum capricornutum, to test the nutritional adequacy of these algae. Comparisons were made at a standard temperature (17°C) and food supply level (1 mgCl^?1).
• 2 All diets other than Scenedesmus and Selenastrum supported complete naupliar development at broadly comparable times within and between calanoids, apart from greatly protracted Dn values for M. meridianus on Cyclotella. Dc durations were more variable between diet types, and both Chlamydomonas and Cyclotella were inferior or inadequate for copepodid development.
• 3 Both naupliar and copepodid stages ingested radiolabelled Scenedesmus and Selenastrum readily. Comparative incorporation rate measures of Selenastrum and Cryptomonas respectively exceeded estimated metabolic maintenance needs of stage 3/4 nauplii of T. spectabilis by some 56% and 790%. Scope for growth (‘surplus’ energy) was accordingly fourteen-fold greater on Cryptomonas than on Selenastrum /Scenedesmus. The dietary inadequacy of these two green algae is thus attributed largely to low digestibility, and perhaps some biochemical deficiency.

     

Studies on two species of Asellus in Rutland Water

The study comprised a comparison of the ecology of two species of Asellus (A. aquaticus and A. meridianus), and had two main aims. First the energy budget of the population of A. aquaticus, which is one of the most abundant species in the reservoir was assessed. Secondly, the two species appear to be ecologically very similar and it has been assumed by many workers that they are in competition. The study aimed to investigate how these two species might be able to coexist.The population dynamics of both species and the interaction between them is under study, as are their relations with the other benthic animals recorded in the reservoir (see Bullock et al. 1982). The sampling programme to cover variations in depth and substratum is also described by Bullock et al. 1982. A. aquaticus occurs in both arms while A. meridianus exists only in the south arm. A preliminary examination of the available data reveals that the density of A. aquaticus has increased in the south arm while the density of A. meridianus decreased drastically in February 1980. Since then low numbers of A. meridianus have been recorded every month even in the summer (breeding) season. It is noteworthy that simultaneously the number of predators, particularly Helobdella stagnalis, increased in comparison with previous years.It was therefore decided to study the predation on Asellus in the laboratory as well as in the field by using a serological technique. Antisera were produced against each species of Asellus by injections into rabbits of precipitated proteins (antigens). Thus a positive reaction obtained from a homogenised predator when tested with the specific antiserum indicates which species of Asellus had been consumed and the percentage of predators which had fed on Asellus in every sample could be calculated. The results obtained to date reveal that considerable numbers of Asellus spp. are removed from the environment by the predators (Helobdella stagnalis, Erpobdella octoculata, Polycelis tenuis. Dendrocoelum lacteum and Dugesia lugubris).Size class structures of the population of both species were constructed to study their life cycles and to estimate the population production. Comparitive respirometry of the two species was carried out at 4 °C, 10 °C and 16 °C, using a Gilson differential respirometer. This study aimed firstly to assess one of the essential parameters in the energy budget study of A. aquaticus and secondly, since A. aquaticus appears to be more active than A. meridianus, it would be expected that a comparison of their metabolic rate at different temperature would reveal marked differences between two species. It was found that there was no significant difference between the two species at 4 °C and 10 °C, but A. aquaticus had a significantly higher metabolic rate than A. meridianus at 16 °C.Consumption and assimilation of decaying oak leaves and of Cladophora glomerata (both of which are available in the environment) by two species of Asellus are being measured at present in the laboratory at three different temperatures (4 °C, 10 °C and 16 °C), and will contribute to the estimation of energy budgets.     

Phylogeography,phylogeny, and taxonomical revision of the Midday jird (Meriones meridianus) species complex from Dzungaria

The Midday jird Meriones meridianussensu lato is a widely distributed and highly variable species complex, whose taxonomy is still controversial despite several genetic and morphological studies. Dzungaria is a crucial region for understanding the phylogeny and phylogeography of this species complex. In this work, the genetic variation of M. meridianus in Dzungaria and adjacent areas was studied based on mitochondrial (Cytb) and nuclear (BRCA1 and IRBP) genes. To compare morphological and genetic differentiation among lineages, craniological variation of the genotyped specimens was examined. Moreover, environmental data were used to estimate the most probable dispersal routes of M. meridianus clades in the studied area. Three clades of M. meridianus with interspecific level of differentiation were found and treated as distinct species: M. psammophilus (Milne-Edwards, 1871); M. meridianus (Pallas, 1773); and M. penicilliger (Heptner, 1933). The distribution ranges of all three species overlap in Dzungaria. According to the molecular data, M. psammophilus and M. meridianus are sister taxa that diverged ca. 500 kya, while M. penicilliger separated from the common ancestor of the other two lineages ca. 800 kya. These three species have significantly different cranial measurements. Moreover, traces of hybridization between M. psammophilus and M. meridianus were detected, but not between M. penicilliger and the other two species. Finally, the dispersal scenarios for M. psammophilus, M. meridianus, and M. penicilliger are herein discussed. It is suggested that M. meridianusand M. penicilligerindependently colonized Dzungaria from the west via Dzungarian gates.     

Oxygen consumption in Tardigrada from Spitsbergen

Summary Oxygen consumption was measured in seven species of Tardigrada (Doryphoribius smreczynskii, Diphascon spitzbergensis, Macrobiotus islandicus, M. echinogenitus, M. harmswothi, M. spectabilis and M. dispar) from the Spitzbergen tundar. The metabolic rate was measured at 2°, 6° and 10°C. At 6°C it ranged from 0.055 (D. smreczynskii) to 0.101 mm³·10^-3/g·10^-6h (M. harmswothi). In D. smreczynskii the phenomenon of relative thermal independence was observed at a temperature range of 2°–6°C. The dependence of oxygen consumption (R in mm³·10^-3·individ^-1·h^-1) on body weight (W in g·10^-6) for the latter species at 2°C was R=0.088·W^0.82.     

Microbial nitrogen fixation in the gastro-intestinal tract of Kalmykia gerbils (<Emphasis Type="Italic">M. tamariscinus</Emphasis> and <Emphasis Type="Italic">Meriones meridianus</Emphasis>)

The nitrogen-fixing activity, nitrogen (N) and carbon (C) contents, and the number of microorganisms in the forestomach, cecum, and colon were detected in two gerbil species, granivorous Meriones meridianus and M. tamariscinus, which consume a large amount of green parts of the plants. M. meridianus had higher levels of nitrogen-fixation activity in all investigated parts of the gastro-intestinal tract compared with M. tamariscinus. The highest levels were detected in the colon of M. meridianus. The C/N ratios in the forestomach of M. tamariscinus were higher than in M. meridianus, which is consistent with the greater role of the green parts of plants in its diet. A gradual increase in the nitrogen content from the forestomach to the colon of M. tamariscinus was noted. The amount of microorganisms in the forestomach and intestine of the studied gerbil species was similar.     

Geographical variation in the cranial measurements of the midday jird Meriones meridianus (Rodentia: Muridae) and its taxonomic implications

Cranial variation was studied across the geographical range of the Meriones meridianus species complex using 665 specimens from 112 localities. Morphometric results were compared with previously published data on genetic variation. Unsupervised model‐based clustering analysis implemented in Mclust software was employed to identify the number and content of morphological clusters. Three clearly defined morphological groups corresponding to mtDNA clades were found. The results of the morphometric analysis are consistent with the hypothesis that these 3 groups should be treated as distinct species; specifically, M. psammophilus Milne‐Edwards, 1871, M. penicilliger Heptner, 1933 and M. meridianus Pallas, 1773. M. psammophilus inhabits the Mongolian–Chinese part of the superspecies range, except for the Mongolian Dzungaria region, which is inhabited by M. meridianus. The range of the latter species extends westwards to north‐west Kazakhstan and Kalmykia. M. penicilliger inhabits the southern part of the superspecies range from Tian Shan to Turkmenistan. M. dahli is craniometrically similar to M. meridianus; hence, its species status remains questionable.     

Seasonal variations in the immune system of the tench,Tinca tinca (Cyprinidae): proliferative response of lymphocytes induced by mitogens

The proliferation of tench lymphocytes induced by mitogens was studied during the four seasons of the year. Fish were maintained under natural conditions of photoperiod and temperature (mean ± SD: 12±2°C in winter, 22±3°C in spring, 30±3°C in summer and 21±3°C in autumn). Cultures were performed in vitro at 22°C in all seasons and the results were compared. Subsequently, in seasons with extreme water temperatures, cultures in vitro were performed at the same temperature as that of the water (12°C in winter and 30°C in summer) and the results were compared seasonally at the seasonal temperature, i.e. at 22°C in spring, 30°C in summer, 22°C in autumn and 12°C in winter. Phytohemagglutinin, concanavalin A, lipolisaccharide from E. coli and pokeweed mitogen were used as mitogens. Studies performed at 22°C as assay temperature in all seasons showed profound seasonal changes: while in spring, summer and autumn the mitogenic response of lymphocytes to phytohemagglutinin, concanavalin A, lipolisaccharide from E. coli and pokeweed mitogen was very low, during winter the results obtained were significantly higher. However, when the assays were performed at the corresponding seasonal temperature the differences were not as pronounced between the different seasons, and the mitogenic responses of lymphocytes were found to be the lowest during the winter and the highest during the summer with all mitogens used. This fact suggests that immunosuppression occurs in winter and an immunostimulation occurs in summer. However, the higher response found in winter when assaying at 22°C suggests that this property of lymphocytes needs an assay temperature higher than the in vivo temperature in order to observe accurate mitogenic responses.Abbreviations Con A concanavalin A - cpm counts per minute - LPS E. coli lipolisaccharide - MS222 tricainemethane sulphonate - PBS phosphate-buffered saline - PHA phytohemagglutinin - PWM pokeweed mitogen - SI stimulation index     

Biology of the shore fly Scatella stagnalis in rockwool under greenhouse conditions

The development times and survival of immature stages in rockwool and the fecundity and longevity of adult Scatella stagnalis were determined and stage-specific life-tables constructed for the species at constant 20 and 25 °C and at a fluctuating temperature (23–34 °C, mean 28.5 °C). Development time from egg to adult decreased with temperature, being 15.9±0.1 days at 20 °C, 11.4±0.1 days at 25 °C and 10.1±0.2 days at fluctuating temperature with mean of 28.5 °C. The lower threshold for egg-to-adult development was 6.4±2.7 °C and the total quantity of thermal energy required to complete development was 212.8±.0 °C. The proportion of females in two populations studied was 0.521. High temperature increased the mortality of pupae from 7% (20 °C) and 10% (25 °C) to 29% at 28.5 °C. At 25 °C, female longevity was 15.5±0.7 days and fecundity 315±19 eggs/female (20.4 eggs/female/day). Males lived for 22.0±1.1 days. At constant 25 °C, the net reproductive rate was 126.1 female eggs/female, generation time was 18.4 days, the doubling time of the population 5.3 days, and the intrinsic rate of increase (r _m) 0.263 day^–1.     

Regeneration via somatic embryogenesis from leaf basal segments and genetic transformation of bread and emmer wheat by particle bombardment

Direct gene transformation methods such as microprojectile bombardment have been successfully employed for obtaining transgenics in cereals in general and wheat in particular. As success of any transformation strategy depends largely upon the regeneration capability of the target explant, the present investigation employs leaf basal segments to achieve high regeneration response via somatic embryogenesis. Basal segments of 5-day-old seedlings of T. aestivum var. CPAN1676 and T. dicoccum var. DDK1001 were cultured on callusing medium for 3 weeks at 26 ± 1 °C, discontinuous light followed by a culture period of 15 days at 21 ± 1 °C in continuous light. The calli were then transferred to auxin-free medium for regeneration in discontinuous light at 26 ± 1 °C. Regeneration via somatic embryogenesis was observed within 2 weeks in T. aestivum var. CPAN1676 and T. dicoccum var. DDK1001 (68 and 82%, respectively). This embryogenic calli were employed further to obtain hygromycin resistance by particle bombardment in T. aestivum and T. dicoccum. A transformation efficiency of 8.6, 7.5 and 4.9% was obtained in T. aestivum var. CPAN1676, PBW343 and T. dicoccum DDK1001, respectively. Presence of the transgene hptII (hygromycin) in T ₀ plants was confirmed by Southern hybridization.     

Cold tolerance in nematodes

Summary The nematodesTrichostrongylus colubriformis (J3),Ditylenchus dipsaci (J4) andPanagrellus silusae (adults) are freezing-susceptible but can avoid freezing by supercooling. Their mean supercooling points were –30.0±0.7°C forT. colubriformis, –21.7±0.7°C forD. dipsaci and –20.7±0.84°C forP. silusae. T. colubriformis andD. dipsaci could prevent seeding by external ice butP. silusae could not. The glycerol concentrations of these nematodes are considered to be too low to have a significant antifreeze effect.Abbreviations J3 3rd-stage juvenile - J4 4th stage juvenile - SEM standard error of the mean - T ₅₀ 50% survival temperature     

Life table and biological characteristics of Macrolophus pygmaeus when feeding on Myzus persicae and Trialeurodes vaporariorum

The life table and biological characteristics of the predatory bug Macrolophus pygmaeus Rambur (Hemiptera: Miridae) were studied when the bugs were fed with Myzus persicae (Sulzer) (Homoptera: Aphididae) feeding on eggplant and with Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) feeding on tomato plants. The tests were done at five temperatures between 15 and 30 °C, using a L16:D8 photoperiod and 65 ± 5% r.h. Most eggs (range 85 to 90%) hatched at 15 and 20 °C. Incubation period was shortest at 27.5 °C (8.45 and 8.38 days on eggplant and tomato, respectively). Preoviposition was also shortest at 27.5 °C (5.10 and 4.75 days on eggplant and tomato, respectively) whereas fecundity was highest at 20 °C (213.90 and 228.25 eggs on eggplant and tomato, respectively). Maximum longevity of females was at 15 °C (122.40 and 129.35 days on eggplant and tomato, respectively). Mean generation time was longest at 15 °C on both host plants (122.75 and 124.64 days, respectively). The intrinsic rate of increase of M. pygmaeus was highest at 27.5 °C with similar values on eggplant (0.0981 day^–1) and tomato (0.1040 day^–1). Doubling time was shortest at 27.5 °C (7.06 and 6.67 days on eggplant and tomato, respectively) and, also, finite rate of increase was highest at 27.5 °C (1.1031 and 1.1096 on eggplant and tomato, respectively). The results show that the predator M. pygmaeus develops well on the aphid M. persicae or on the whitefly T. vaporariorum, both of which are important pests of vegetable crops. This predator is also well adapted to the temperatures that occur both in greenhouses and in the open field in the Mediterranean region. Compared to other natural enemies of whiteflies, such as Encarsia formosa Gahan (Hymenoptera: Aphelinidae), Macrolophus pygmaeus can increase at relatively low temperatures.     

Evidence that mass trapping suppresses pink bollworm populations in cotton fields

Both thelytokous and arrhenotokous Trichogramma minutum were collected from eggs of the spruce budmoth, Zeiraphera canadensis in New Brunswick, Canada and their phenotypic traits compared for use in biological control. The lower threshold temperature for development of thelytokous and arrhenotokous parasitoids was 9.7 and 10.1 °C, respectively; the former required significantly higher degree-days for development from egg to adult (–x±SE=165.1±5.8 °D) than the latter (128.1±4.9 °D). Thelytokous and arrhenotokous parasitoids had similar forewing length (0.49±0.01 vs. 0.49±0.01 mm) and adult lifespan (13.3±0.7 vs. 14.0±1.1 days), but significantly different fecundity and sex ratios. Thelytokous females produced fewer offspring (89.5±6.6 vs. 173.9±6.4) and fewer female progeny (77.2±5.4 vs. 109.8±3.3) despite an overall higher proportion of females (91.6±1.1% vs. 65.4±2.8%) than their arrhenotokous counterparts. Ovarian dissections showed that the number of eggs increased with parasitoid age in arrhenotokous parasitoids but remained steady in thelytokous parasitoids. The variation in ovarian development of the two forms was the major factor contributing to the differences in fecundity. Thelytokous parasitoids were more host-specific than arrhenotokous ones; when offered eight host species, the former rejected three whereas the latter rejected only one. Thelytokous parasitoids survived better than arrhenotokous ones when stored from 30 to 150 days at 4 °C. Thelytokous females were slower at initiating flight after emergence than arrhenotokous females but maintained flight activity longer (6 h). These results indicate that thelytokous T. minutum are different from their arrhenotokous counterparts physiologically, biologically and ecologically and that they may play different roles in the field. The potential for using thelytokous parasitoids in biological control programs is discussed.     

Spatial distribution of resting stages,rate of emergence from diapause and times to adulthood and to the appearance of the first clutch in 3 species of cyclopoid copepods

The spatial distribution of dormant copepodids of 3 species of cyclopoid copepods — Cyclops vicinus, Mesocyclops leuckarti and Thermocyclops crassus — was studied in 4 small lakes in South Germany. The rate of emergence from diapause and times from the resting stage to adulthood and from adulthood to the appearance of the first clutch was studied at 4 constant temperatures (5, 10, 15, 20 °C) in the laboratory. Resting stages of C. vicinus were always concentrated in the deepest parts of the lakes and were found relatively deep in the mud. M. leuckarti- and T. crassus-copepodids preferred shallow areas in deep lakes but were concentrated in the deep areas in shallow lakes. Copepodids of both species were always concentrated in the uppermost mud layers.Rate of emergence from diapause was strongly temperature-dependent. At high temperatures (20 °C) copepodids of all species under study emerged within 2 weeks. At lower temperatures C. vicinus copepodids showed the highest rate of emergence. At 5 to 10 °C only few M. leuckarti- and T. crassus-copepodids had emerged after the investigation period (7 weeks). Both C. vicinus and T. crassus showed the highest rate of emergence at the natural end of diapause but even at that time only few T. crassus-copepodids emerged at 5 °C. Times to adulthood at 5 °C were shortest in C. vicinus. At higher temperatures this species was passed by M. leuckarti. Times from adulthood to the appearance of the first clutch at 5–15 °C were shortest in C. vicinus. T. crassus produced no clutch at 5 and 10 °C.     

Egg production in response to combined alternative foods by the predator Coccinella transversalis

The peformance of the parasitoid Anagyrus kamali Moursi [Hymenoptera: Encyrtidae], as a function of host density, temperature, and photoperiod was investigated with the objective to optimize a mass-rearing system in the context of a biological control program. The number of hosts parasitized at densities varying from 2–100 hibiscus mealybug (HMB), Maconellicoccus hirsutus Green [Homoptera: Pseudococcidae], corresponded to a type II-III functional response in fixed-time conditions and a type III in variable-time conditions. Twenty-six percent of the oviposited eggs led to progeny emergence with a sex ratio of 0.49±0.102 (M/F), regardless of host density. Fecundity and oviposition period under six abiotic combinations (i.e., two temperatures (26±2 °C and 32±2 °C) and three photoperiods (L0:D24, L12:D12, L24:D0)) were measured. Lifetime fecundity and reproductive life were significantly affected by temperature and photoperiod conditions. Optimum female parasitoid lifetime fecundity was attained at 26±2 °C, L0:D24 with an average of 116.1±17.43 eggs. At 32±2 °C, L24:D0 and L12:D12, an average of 79.4±34.57 and 85.8±35.81 eggs were laid, respectively. Reproductive longevity was maximal at 26±2 °C, L0:D24 with 12±4.85 days of oviposition. Because the parasite A. kamali can be reared optimally without light, this may save tremendous energy costs.     

Preliminary studies on the biology of the pest mite Luciaphorus auriculariae (Acari: Pygmephoridae) infesting Jew's ear mushroom Auricularia polytricha in China

The mite, Luciaphorus auriculariae Gao et al. recently discovered in Fujian Province, China, is regarded as a destructive mite to the commercial production of jew's ear mushroom, Auricularia polytricha, causing a 10–50% to total loss of the crop.There are only two phases in the life cycle of L. auriculariae. Eggs develop directly into adults within the physogastric hysterosoma of the female. Mating takes place both within and outside of the hysterosoma and lasts 7–12 seconds. Under normal conditions, a male mates up to 20 times, but a female, only once. When the hysterosoma bursts, fertilized females disperse rapidly in search of food. As soon as a favourable location is found, they project their gnathosomas and their hysterosomas begin to swell.At controlled temperatures of 20°C, 25°C, 30°C, and 35°C, the egg phase lasted 13.6±3.2,6.6±0.6, 4.5±0.8 and 3.0±0.9 days; the adult phase, 26.6±4.3, 12.6±2.2, 8.8±0.2 and 7.0±0.7 days, and the progeny totaled 125.4±90.1, 128.1±119.1, 163.9±92.1 and 77.3±81.5, respectively.Laboratory tests showed that in the course of normal development and reproduction, L auriculariae can feed on both the mycelia and sporophores of A. polytricha, A. auricula and Flammulina velutipes, but not on the mycelia of Agaricus bisporus, Pleurotus ostreatus, Tremella fuciformis, or Lentinus edodes or the sporophores of L. edodes.When living conditions become unfavourable, the walls of the physogastric hysterosoma harden and form a crust around the cavity, delaying further egg development and protecting newly emerged adults.     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

Location,reproduction and movement of Neoseiulus californicus (Acari: Phytoseiidae) during the autumn,winter and spring in orchards in the south of France

Field samples and experiments conducted in apple orchards in the south of France showed that Neoseiulus californicus (McGregor) searched for prey on the trees and in the ground cover as late as mid-November 1993, and at least as early in the spring as the end of February 1994. Overwintering females fed, expanded and produced viable eggs within 7.9±0.3 (SE) days given the natural light regime, adequate food and temperatures of 17.0±20.6°C. The first generation of N. californicus developed in the field during March and April 1994. N. californicus nymphs, females and males readily moved over bare ground and through a grass ground cover to trap plants located on stakes 1 m above the ground. In the laboratory, the rate of movement of adult females on 0.5 mm copper wire was a linear function of temperature above a threshold of 11.9±0.9°C. At 25°C they travelled 10 m per h. The migration rate of N. californicus to trap plants on stakes placed in an orchard 13 Apr. increased in 2 weeks from 0.07 to 0.57 predators/trap plant/degree-day, while the migration rate to plants placed directly in the ground cover was 1.45 predators/trap plant/degree-day. The largest population of N. californicus in April occurred on Barley, Hordeum murinum L. This plant produces pollen in April and May, and may be useful in biocontrol programs.