Determination of seed viability of eight wild Saudi Arabian species by germination and X-ray tests

Our purpose was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of eight wild species (Salvia spinosa, Salvia aegyptiaca, Ochradenus baccatus, Ochradenus arabicus, Suaeda aegyptiaca, Suaeda vermiculata, Prosopisfarcta and Panicumturgidum) from Saudi Arabia. Several days were required to determine viability of all eight species via germination tests, while immediate results on filled/viable seeds were obtained with the X-ray test. Seeds of all the species, except Sa.aegyptiaca, showed high viability in both the germination (98–70% at 25/15 °C, 93–66% at 35/25 °C) and X-ray (100–75%) test. Furthermore, there was general agreement between the germination (10% at 25/15 °C and 8% at 35/25 °C) and X-ray (5%) tests that seed viability of Sa.aegyptiaca was very low, and X-ray analysis revealed that this was due to poor embryo development. Seeds of P.farcta have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (98% at 25/15 °C and 93% at 35/25 °C) and X-ray (98%) test. Most of the nongerminated seeds of the eight species except those of Sa.aegyptiaca were alive as judged by the tetrazolium test (TZ). Thus, for the eight species examined, the X-ray test was a good and rapid predictor of seed viability.     

Germination response and viability of an endangered tropical conifer Widdringtonia whytei seeds to temperature and light

The tropical conifer Widdringtonia whytei Rendle is an endangered species endemic to Mulanje Mountain in Malawi. A study was conducted for the first time under controlled conditions in order to assess the effects of temperature and light on germination and viability of W. whytei seeds. Seeds incubated at a constant temperature of 20 °C attained the highest cumulative germination percentage (100%) followed by 87% germination under fluctuating temperatures of 15 °C night/25 °C day. No seed germination occurred at temperatures below 15 °C. Seeds that failed to germinate at temperatures below 15 °C showed the highest (> 90%) viability compared to the seeds incubated at 25 °C (60%). Across temperature regimes, germination was significantly higher under light (44.7%) than dark (35.6%) conditions. It is concluded that temperature is one of the critical factors for germination of W. whytei seed. The ability of W. whytei seeds to germinate both in light and darkness implies that the species would unlikely form a persistent soil seed bank, an attribute which is common in species that survive in habitats frequently disturbed by fires.     

Temperature requirements for dormancy break and seed germination vary greatly among 14 wetland Carex species

We evaluated dormancy loss in seeds of 14 Carex species (C. atherodes, C. brevior, C. comosa, C. cristatella, C. cryptolepis, C. granularis, C. hystericina, C. lacustris, C. pellita, C. scoparia, C. stipata, C. stricta, C. utriculata, C. vulpinoidea) under growing season and stratification conditions and determined the temperature requirements for germination. Seeds were germinated for 1 year at a diel temperature regime (5/1 °C, 14/1 °C, 22/8 °C, or 27/15 °C) or a seasonal regime (seeds moved among the four diel regimes to mimic seasonal temperatures). All species had conditionally dormant seeds at maturity. The optimal temperature for germination of most species was 27/15 °C. The 14 species were grouped by their seed viability, dormancy, and germination with a Seed Regeneration Index (SRI; range 0–1) using the results of this study and a previously published paper on stratification effects on Carex seed dormancy and germination. The eight species that had an SRI value >0.5 (C. brevior, C. comosa, C. cristatella, C. cryptolepis, C. hystericina, C. scoparia, C. stipata, C. vulpinoidea) had high seed viability (>60%) and required little to no stratification to germinate readily over a broad range of temperatures. The six species with an SRI value <0.5 (C. atherodes, C. granularis, C. lacustris, C. pellita, C. stricta, C. utriculata) generally had low seed viability (<50% and often <1%) and required stratification or particular temperatures (35/30 °C or 5/1 °C for C. stricta; 35/30 °C for C. utriculata; 27/15 °C for C. atherodes, C. lacustris, C. pellita; 5/1 °C for C. granularis) for germination ≥50%. These six species will require more attention from restoration practitioners to ensure that there are sufficient viable seeds to meet revegetation goals, that dormancy break is achieved, and that seeds are sown when temperatures are optimal for germination. The different seed germination syndromes that we found for these Carex species likely contribute to variable seed bank formation and emergence patterns, and species coexistence.     

Seed storage and germination in Kumara plicatilis,a tree aloe endemic to mountain fynbos in the Boland,south-western Cape,South Africa

Seed storage under appropriate conditions is a relatively inexpensive means of safeguarding plant genetic material for ex situ conservation. Post-storage germination trials are used to determine the viability of stored seeds, and hence the efficacy of the particular storage treatment. Kumara plicatilis (= Aloe plicatilis) is a tree aloe endemic to mountain fynbos in the Boland, south-western Cape. The viability and germination behaviour of K. plicatilis seeds were assessed for seeds stored for four and nine months at − 80 °C, 4 °C, 25 °C and under ambient conditions in a laboratory. Seeds were germinated under controlled conditions and germination rates and percentages determined. Ungerminated seeds were tested for viability using tetrazolium salt. Seed viability was not significantly reduced during storage. Seeds stored at − 80 °C for four and nine months exhibited the fastest germination rate overall (both 5.9 ± 0.3 weeks, mean ± S.E.), and slowest was for seeds stored under ambient conditions for four and nine months (both 7.8 ± 0.4 weeks). All seed lots showed similar percentage germination after four months of storage (78.0–90.4%). The highest percentage germination overall was for seeds stored at − 80 °C for four months (90.4%) and the lowest was for seeds kept at 4 °C and − 80 °C for nine months (39.2 and 39.6%, respectively). Respective percentage viability for ungerminated seeds in these two treatments was 82% and 87%, respectively, indicating the induction of secondary dormancy. Induced dormancy triggered by protracted cold temperatures may be an adaptation that enables seeds to survive prolonged extreme conditions that are unfavourable for germination. Further research on the long-term storage of aloe seeds would be beneficial for developing long-term seed storage and germination testing protocols for ex situ conservation.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Temperature requirements for seed germination of Pereskia aculeata and Pereskia grandifolia

Pereskia aculeata and Pereskia grandifolia have been studied widely due to their high nutritional and therapeutic values. However, little is known about the biological requirements of their seeds for the various germination factors. Thus, this experiment aimed to evaluate the thermal effects on the germination of these species at the temperatures of 24 °C, 27 °C, 30 °C, 33 °C and 36 °C. After verification of the existence of differences in the performance of germination, a non-linear regression was carried out, relating the germination to temperature and identifying its point of maximum efficiency. We found that the lowest synchronization indexes of germination were observed close to 30 °C. The best germination response of the P. aculeata and P. grandifolia was observed at 30 °C and 33 °C, respectively, with greater germination strength and fewer days to attain 63.21% of germinations. The results obtained from the germination of P. aculeata and P. grandifolia can be described by the Weindull distribution model with three parameters, as proposed by Carneiro and Guedes (1992).     

Effect of yak rumen content treatments on seed germination of 11 alpine meadow species on the Qinghai-Tibetan Plateau

The Qinghai-Tibetan Plateau is located in the ‘Third Pole’ of the world, characterized by a harsh environment. Despite this, the alpine meadow ecosystem have developed over a wide area but serious grassland degradation is threatening the ecological environment on the Plateau. Recruitment of new plants to the population, via germination and establishment, is vital to plant community survival. Previous work on the seeds in this area has mainly focused on community-wide germination strategies, seed germination characteristics and their correlations with seed size and seed mass. However, there have been no studies on the effects of soaking in rumen contents on the plant seed germination characteristics of alpine meadow species. The present study had two main objectives: (i) to determine the effect of fresh rumen content from yaks on seed germination characteristics and seedling growth of species common to the eastern Tibetan Plateau alpine meadow, and (ii) to develop an effective method to enhance seed germination. Seeds of 11 common species were collected together with fresh rumen content from three yaks that grazed there. Seed germination tests were conducted after they had been soaked in rumen content for one of six soaking periods (12, 24, 36, 48, 60 or 72 h). The seeds were incubated under natural light conditions of 8 h light at 25 °C and 16 h darkness at 15 °C, for the germination period of 34 days. The results showed that seed germination and seedling growth were affected by soaking time, seed coat completeness and seed type. After soaking in rumen content, the germination percentages of scarified (peeled or with the seed coat cut through) seeds of some species (true seeds Oxytropis ochrocephala and Medicago ruthenia var inschanica, nutlet Carex enervis, achenes Anemone rivularis and Polygonum sibiricum) and complete seeds of C. enervis, and A. rivularis were improved but the duration of soaking was also important. Seed germination of caryopsis Achnatherum inebrians (a toxic grass) was significantly inhibited by any exposure to rumen fluids. Scarified seeds generally had higher germination percentages than complete ones after treatment, but with the increase in soaking time, germination percentages declined and scarified seeds were more sensitive to the treatment than the complete seeds. After soaking in yak rumen content, the germination indices of scarified M. ruthenia at 12 h treatment, O. ochrocephala and achene Rumex acetosa at 12–24 h treatment, nutlet Kobresia humilis at 24 h treatment, P. sibiricum at 24–48 h treatment, C. enervis at 12–48 h treatment and A. rivularis at 12–60 h treatment were significantly higher than the control (P < 0.05), while the germination indices of complete C. enervis seeds at 12 h and 36 h treatment, and A. rivularis at 12–60 h treatment were significantly higher compared with the control. The germination indices of other species gradually decreased with the increase in soaking time. We concluded that yak rumen digestion could enhance, inhibit or not affect seed germination and seedling growth of the alpine meadow species, which might influence seedling recruitment, interspecific competition, and the plant community structure of the eastern Tibetan Plateau alpine meadow. Overall, yak digestion has a positive effect on alpine meadow seed germination and seed dispersal.     

Smoke-water effect on the germination of Amazonian tree species

Smoke stimulates seed germination of a range of species from ecosystems that may or may not be fire prone. We evaluated the effects of smoke-water on germination of ten tree species of economic value in the Amazon region. Two materials were burnt to produce smoke-water: germination paper and the wood of Cecropia palmata Willd. Seven dilutions of the solutions were tested. Seeds of nine forest trees were germinated under controlled laboratory conditions (25 °C ± 2 °C) in the laboratory. Bertholletia excelsa Humb. & Bonpl., was tested in the nursery (approximately 25–36 °C) because of its large seeds. Irrespective of the material burned, smoke-water significantly increased seed germination of three species: Cordia goeldiana Hub., Ochroma pyramidale (Cav. ex Lam.) Urb. and Jacaranda copaia (Aubl.) D. Don. and there was a significant inhibitory effect on Swietenia macrophylla King. Germination was accelerated by smoke in J. copaia, B. excelsa and Bellucia grossularioides (L.) Triana. The most pronounced effect was observed in B. excelsa, as the mean germination time of 108 d (control) was reduced to 76 d with smoke-water made from germination paper (dilution of 1:25) and to 61 d with the one from Cecropia wood (dilution of 1:250). For five of the ten species studied, smoke-water either increased or accelerated seed germination, irrespective of the materials used for its production. Seeds with low vigour and prolonged germination time seemed to be more receptive to smoke.     

Impact of temperature on olive (Olea europaea L.) pollen performance in relation to relative humidity and genotype

Olive varieties ‘Koroneiki’, ‘Kalamata’, ‘Mastoidis’ and ‘Amigdalolia’ were employed in two experiments for 3 years to assess the effect of temperature on olive pollen germination and tube growth in relation to relative humidity and genotype. Pollen samples were subjected to pre-incubation at 10, 20, 30 or 40 °C in combination with decreased air relative humidity – 80, 40, 30 or 20%, respectively – for 24 h to simulate temperature stress that is observed during pollen dispersal; and subsequently in vitro cultured. In the second experiment, pollen was exposed at 15, 20, 25 and 30 °C for 24 h in vitro to evaluate pollen response in conditions of water and nutrients availability and to determine the optimum pollen germination and tube growth temperatures for each cultivar. The highest pre-incubation temperature treatment (40 °C) prevented pollen germination in ‘Koroneiki’ and ‘Mastoidis’, with the less affected varieties (‘Amigdalolia’ and ‘Kalamata’) having average germination percentages of only 7.6 and 2%, respectively. Pre-incubation at 30 °C had a negative impact on pollen germination in ‘Koroneiki’ (?65%), ‘Kalamata’ (?20%) and ‘Amigdalolia’ (?72%) compared to the control (20 °C). Pollen pre-incubation at 40 °C decreased significantly the pollen tube length in ‘Kalamata’ (?50%) and ‘Amigdalolia’ (?52%). In the second experiment, in vitro pollen germination increased after incubation at 25 °C for ‘Koroneiki’ (+6%), ‘Mastoidis’ (+52%), ‘Kalamata’ (+10%) and ‘Amigdalolia’ (+10%) compared to the control (20 °C). At 30 °C germination percentages for ‘Mastoidis’, ‘Kalamata’ and ‘Amigdalolia’ were 8, 6 and 14% higher, respectively, compared to the control (20 °C). Pollen tube length also increased with incubation temperature for all of the studied cultivars. Based on the cumulative stress response index (CSRI) that was calculated for high temperature stress the varieties were classified: ‘Mastoidis’ and ‘Kalamata’ as tolerant and ‘Koroneiki’ and ‘Amigdalolia’ as intermediate at 30 °C while all studied cultivars were sensitive at 40 °C. The observed strong genotype-differentiated response in high and low temperature stress could be exploited by plant breeders towards producing new tolerant olive varieties.     

Role of calcium in alleviating effect of salinity on germination of Phragmites karka seeds

Phragmites karka (Retz.) Trin, ex. steud, a perennial reed with creeping rhizome from the family Poaceae, is distributed as pure population in brackish water swamps. Populations primarily propagate using ramets but also produce numerous seeds which form part of the seed bank after dispersal and are exposed to extremes of temperature, drought, and salinity stress. Seeds were germinated under a range of salinity (0, 100, 200, 300, 400, 500 mM NaCl) and temperature (10/20 °C, 15/25 °C, 20/30 °C, 25/35 °C, night/day) regimes in 12 h light:12 h dark photoperiod or in complete darkness with 0, 5, 10, 25 mM CaCl₂. Salinity, absence of light and high temperature (25/35 °C) reduced germination while calcium generally reversed this effect, more so at cooler temperature regimes. Calcareous soil around Karachi would help alleviate the salinity effect on the germination of P. karka and facilitate its survival.     

Effect of variable dew temperatures on infection of green foxtail by Pyricularia setariae,Drechslera gigantea,and Exserohilum rostratum

A thermogradient apparatus was used to investigate the effect of variable dew temperatures on infection of green foxtail by the indigenous pathogen Pyricularia setariae (Ps) and the exotic pathogens Drechslera gigantea (Dg), and Exserohilum rostratum (Er) from the southern USA that showed bioherbicide potential against several grassy weeds. This device is capable of creating multiple diurnal temperature cycles, mimicking daily temperature fluctuations that occur under field conditions. Seven temperature regimes, i.e., 15/10 °C, 20/5 °C, 20/15 °C, 25/10 °C, 25/20 °C, 30/15 °C, and 30/25 °C (maximum/minimum), were used with temperature cycling from maximum to minimum and then back up to maximum in a 24 h period. Ps and Dg were much more virulent than Er on green foxtail, resulting in higher levels of disease and weed control. Dg was little affected by the dew temperatures in terms of plant infection and was more efficacious than Ps under cooler dew temperatures (15/10 °C and 20/5 °C), causing twice as much disease. This greater amount of disease coincided with higher conidial germination, appressorial formation and infection-hypha frequency by Dg at the lower temperatures. The efficacy of Ps improved as dew temperature increased, accompanied by a higher percentage of germination and more frequent appressorial production. Dg caused severe disease 2 d after inoculation whereas Ps required 4 d to initiate disease symptoms. These observations suggest that Dg is a superior candidate than Ps for green foxtail control on the Canadian prairies.     

Biology and thermal requirements of Chrysoperla genanigra (Neuroptera: Chrysopidae) reared on Sitotroga cerealella (Lepidoptera: Gelechiidae) eggs

Chrysoperla genanigra Freitas is a common green lacewing associated with melon pests in the Northeastern Brazil. All life stages of this recently described species were studied under a range of constant temperature conditions (17, 21, 25, 29, 33, 35 and 37 °C), a photoperiod of 12 h:12 h (L:D) and 70 ± 10% relative humidity. Adults of C. genanigra were fed on a diet consisting of a 1:1 (v/v) mixture of brewer’s yeast and honey, while larvae were provided with eggs of Sitotroga cerealella (Olivier) ad libitum. The duration of preimaginal development of the species was inversely proportional to temperature and ranged from approximately 63 days at 17 °C to 15 days at 35 °C. The percentage of adult emergence varied from 6.7% at 17 °C to 76.7% at 25 °C, although no larvae were able to complete development at 37 °C. The lower thermal threshold for total preimaginal development was approximately 10.8 °C and the thermal requirement was 336.7 degree-days. Egg production, along with the longevity of both males and females, were significantly affected by temperature. It is concluded that the best temperature for rearing C. genanigra is 25 °C, with the lowest preimaginal mortality and the highest egg production (992.7 eggs/female).     

Optimisation of pollen viability tests for Acacia podalyriifolia and two ploidys of Acacia mearnsii

Acacia mearnsii (black wattle) is a commercially important forestry species in South Africa, grown for its timber as well as its bark. It is, however, also considered to be an alien invader of indigenous vegetation and for this reason the production of a sterile variety would be highly desirable for commercial forestry in South Africa. Previous research on crosses between diploid and tetraploid parent plants to produce triploid progeny has resulted in poor seed set. One possible barrier preventing seed set could be the viability of the pollen used in the cross pollination operations. Thus a study was conducted to test the pollen viability. In vitro agar media germination tests (ACIAR and Brewbaker and Kwack media) were optimised on Acacia podalyriifolia pollen and then used together with vital stain tests (Sigma® DAB peroxidase and p-phenylendiamine) to test pollen germination and viability of A. mearnsii pollen. These were then compared to in vivo pollen germination on the stigma, and were conducted on both diploid and tetraploid pollen mixes. Results showed that the vital stain tests gave significantly (p < 0.05) higher pollen viability than the agar germination tests and were more in agreement with the results from the pollen germination rate on the stigma. For both the diploid and tetraploid pollen mixes tested, there were no significant differences (p > 0.05) between the two agar media germination tests and between the two vital stain tests.     

Effects of seed storage on germination of two succulent desert halophytes with little dormancy and transient seed bank

Seeds of both Salsola imbricata and Haloxylon salicornicum have high germination level and germination speed, and form a transient seed bank in nature. The impacts of storage period and condition on germination level and speed were assessed in the two species. Storage for three months significantly increased both germination level and speed of seeds stored under the different conditions, compared to that of fresh seeds. In both species, nine months storage did not affect germination percentage in cold storage seeds, but completely inhibited it in field seeds. Storage for longer time in room and warm temperatures resulted in significant reduction or complete inhibition in the germination of the two species, so this was more pronounced in H. salicornicum. Storage significantly increased germinate rate index of seeds stored in all conditions till 17 months in S. imbricata and till 12 months in H. salicornicum. In both species, fridge storage had little effects on final germination and germination speed of seeds incubated at the different temperatures, compared to fresh seeds. However, room temperature and warm storages significantly reduced final germination and germination speed at the different temperatures, so the reduction was more pronounced at 35 °C, especially in H. salicornicum.     

The germination characteristics of Alexandrium minutum (Dinophyceae), a toxic dinoflagellate from the Fal estuary (UK)

The germination characteristics of Alexandrium minutum cysts from the Fal estuary were studied at different conditions of temperature (4–24 °C) and salinity (15–35‰) and in the dark and low light intensity (2 μmol^?2 s^?1). Sediment sub-samples were directly cultured and processed at the end of the experiment for counts of non-germinated cysts. A decrease in the number of cysts was interpreted as germination that was calculated by comparison of the number of cysts over time with that of initial counts. The 50% germination time (time at which 50% of the total initial number of cysts had germinated) was calculated for each condition. A. minutum did not germinate in the dark but it germinated under all other conditions studied. Highest germination occurred at salinities of 30 psu and 35 psu and temperatures from 8 °C to 24 °C (germination rate—expressed as the inverse of the 50% germination time: 1.1–1.2). Lowest germination occurred at 15 psu and 4 °C and 24 °C (germination rate: 3.9–3.8). However, little variation in germination rates occurred across the conditions studied. As these conditions represent those likely in the estuary it is probable that A. minutum cysts on the surface of the sediments represent a constant source of cells to the water column and sediment disturbance (revealing buried cysts) could rapidly inoculate the water column with vegetative cells. This data was used to develop a model for Alexandrium germination from coastal sediments.     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

Ecophysiological requirements on seed germination of a Mediterranean perennial grass (Stipa tenacissima L.) under controlled temperatures and water stress

Stipa tenacissima L. (alpha grass) steppes are one of the most representative ecosystems in arid Mediterranean ecosystems. On the one hand these steppes, which are perpetually exposed to climate and strong anthropogenic pressure, have undergone severe degradation. On the other hand, the ability of S. tenacissima to regenerate naturally is significantly reduced. In this study the germination response and seedling emergence of S. tenacissima are examined in relation to the main environmental factors (water stress and temperature) under laboratory-controlled conditions. The main aim of this paper was to investigate the influence of temperature over a temperature range (10 °C–30 °C) and water stress induced by the solutions of polyethylene glycol (PEG)-6000 (0 to − 1.6 MPa) for a period of 30 days, on the germination behavior of S. tenacissima seeds. The results showed that temperatures between 10° and 20 °C seem to be favorable for the germination of this species, with optimum temperatures among accessions found in 20 °C. When seeds were water-stressed, germination severely decreased at − 0.8 MPa, indicating that the accession resistance limits to the water stress, and was completely inhibited at − 1.6 MPa. Consequently, the final germination percentage (FGP) decreased and the mean time germination (MTG) increased. Based on the empirical data of the germination rate, we estimated that the parameters of the thermal time and hydrotime models showed different values in all accessions which proves the difference between accession adaptive capacities.     

Effects of different temperatures on the life history of Evania appendigaster L. (Hymenoptera: Evaniidae), a solitary oothecal parasitoid of Periplaneta americana L. (Dictyoptera: Blattidae)

The influence of temperatures on the life parameters of the solitary oothecal parasitoid Evania appendigaster, was investigated in the laboratory. Parasitized oothecae of Periplaneta americana were left to develop under seven constant temperatures: 15, 17, 20, 25, 30, 35, and 40 °C. At the end, we found that: (i) E. appendigaster was able to complete development within the temperature range of 17–34 °C; (ii) mean adult longevity decreased as temperature increased, with the temperature of 40 °C being fatal in a matter of hours; (iii) males lived longer than females between 15 and 30 °C; (iv) adult emergence rate was the highest at 25 °C, and (v) no wasps emerged at 15 or 40 °C. Non-emerged oothecae contained either unhatched eggs or dead larvae. We determined the theoretical lower developmental threshold and thermal constant for the complete development as 12.9 °C and 584.8 day-degrees for males, and 13.1 °C and 588.2 day-degrees for females, respectively. A good balance between faster development, maximum adult longevity and good egg viability was obtained between 25–30 °C, and that would be the best temperature range for rearing E. appendigaster.     

Overwintering temperatures affect freezing temperatures of turions of aquatic plants

The effect of different overwintering temperatures (2.5 ± 1 °C in a refrigerator or outdoor natural overwintering on wet topsoil with weak frosts) on the freezing temperature and survival rate of turions of 10 aquatic plant species with different ecological traits (free-floating habit or bottom rooting) was studied using mini thermocouples. Dormant, non-hardened turions of 9 species exhibited freezing within a narrow temperature range of ?7.0 to ?10.2 °C, while Hydrocharis morsus-ranae froze at ?3.6 °C. The survival rate of the turions after the measurements was, however, very low (0–38%). In several species, the freezing temperature of turions at the beginning of germination was not significantly different (at p < 0.05) from the dormant ones. The mean freezing temperature of outdoor hardened turions of 6 species was within a very narrow range of ?2.8 to ?3.3 °C and was thus significantly higher by 4–7 °C (p < 0.0002) than that for the non-hardened turions. It is assumed that the freezing temperatures indicate freezing of the extracellular water. The hardened turions of all 7 species were able to survive mild winter frosts under the topsoil conditions at a rate of 76–100%. These characteristics suggest that the turions of aquatic species can be hardened by weak frosts and that their frost hardiness is based on the shift from frost avoidance in non-hardened turions to frost tolerance.     

New approach for determination of an optimum honeybee colony’s carrying capacity based on productivity and nectar secretion potential of bee forage species

The present study was carried out to determine an optimum honeybee colony’s carrying capacity of selected valleys dominated by Ziziphus spina-christi and Acacia tortilis in the Al-Baha region, Kingdom of Saudi Arabia. The study was conducted based on the assessment of the number of colonies kept, their productivities and the existing productive bee forage resources in the target valleys with its economic implication. In the existing beekeeping practice, the average number of managed honeybee colonies introduced per square kilometer was 530 and 317 during the flowering period of Z. spina-christi and A. tortilis, respectively. Furthermore, the overall ratios of productive bee forage plants to the number of honeybee colonies introduced were 0.55 and 11.12 to Ziziphus trees and A. tortilis shrubs respectively. In the existing situation the average honey production potential of 5.21 and 0.34 kg was recorded per Ziziphus and A. tortilis plants per flowering season, respectively. The present study, revealed that the number of honeybee colonies introduced in relation to the existing bee forage potential was extremely overcrowding which is beyond the carrying capacity of bee forage resources in selected valleys and it has been observed to affect the productivities and subsequent profitability of beekeeping. The study infers that, by keeping the optimum honeybee colony’s carrying capacity of valleys (88 traditional hives/km² or 54 Langstroth hives/km² in Ziziphus field and 72 traditional hives/km² or 44 Langstroth hives/km² in A. tortilis field), profitability of beekeeping can be boosted up to 130.39% and 207.98% during Z. spina-christi and A. tortilis, flowering seasons, respectively.