Comparative biology and life table of Habrobracon hebetor (Hymenoptera: Braconidae) on Anagasta kuehniella (Lepidoptera: Pyralidae) at five constant temperatures

Habrobracon hebetor Say is an ectoparasitoid that has been used as a control agent of various lepidopteran pests. Temperature-dependent life table and thermal characteristics of H. hebetor are important in understanding the dynamics of host–parasitoid relationships and for optimizing biocontrol programmes. The influence of five constant temperatures (15, 20, 25, 30 and 35 °C) on the biology of H. hebetor when parasitizing Anagasta kuehniella Zeller was studied. The survival rate of immature stages increased from 16.67% to 83.81% as temperature increased from 15 to 30 °C and then decreased at 35 °C. Total development time ranged from 45.70 days at 15 °C to 7.10 days at 35 °C. The lower temperature threshold for immature stages varied slightly around a value of 11–12 °C. The net reproductive rate (R₀) values were significantly different among temperatures and the highest value was found at 30 °C (85.10). The high survival rate and net reproductive rate combined with a relatively short generation time at 30 °C resulted in the intrinsic rate of increase (r_m) being highest (0.312 d^?1) at this temperature. Considering the acquired results, the temperature range between 25 and 30 °C was optimal for H. hebetor.     

Overwintering,oversummering, and the effect of extreme temperature and humidity levels on the parasitic waspHungariella peregrina compere (Hymenoptera,Encyrtidae)

Hungariella (Tetracnemus) peregrina Compere 1939 is an internal parasite of the long-tailed mealybugPseudococcus longispinus (Targ. Tozz.) (=P. adonidum L.), which attacks the mealybug chiefly in instars I and II. Development through the egg, larval and pupal stages lasts an average of 29.75 days at 30°C and 79.54 days at 17°C. The sex ratio is 1.3 females to 1 male. The wasp persists in avocado orchards throughout the year and overwinters inside the mealybugs or as an adult. The survival depends on the level and duration of low temperatures, since the wasp's tolerance of high temperatures increases as humidity rises, and high humidity greatly increases the life span. In none of the above respects were females found to differ significantly from males.     

Apical Meristem Tip Culture for Eradication of Flexous Rod Viruses in Yams (Dioscorea alata)

Abstract

Apical meristem tips excised from vines of Dioscorea alata cv. White Lisbon produced normal plantlets when cultured in vitro on Murashige and Skoog basal medium supplemented with a range of auxins and cytokinins. Highest yields were obtained on basal medium supplemented with either 1.0 or 0.5 mg/l 2-naphthaleneacetic acid, in combination with either 0.2 or 0.1 mg/l 6-benzyladenine, respectively. Eradication of flexous rod virus infections was possible only when meristems were excised from mother plants which had been growing at 36 + 1°C for at least 14 days; progeny of plantlets obtained from such meristems remained free of detectable virus infection as judged from symptomless growth for 16 months and electron microscopic examination of both sap and ultrathin sections of leaf tissue.     

Effects of low temperatures on pupal survival of the stone leek leafminer Liriomyza chinensis (Diptera: Agromyzidae)

Abstract

The cold-hardiness of Liriomyza chinensis pupae was measured in the laboratory by observing pupal mortality at low temperatures. Pupal mortality increased with decreasing temperature and with extended cold exposure time. No recently pupated pupae (6 h) were able to survive after 16 days of chilling at 0, 2.5 and 5°C, but 42.9% survival was observed at 10°C. Pupae at different developmental stages showed significant difference in mortality, with very low levels of mortality observed for older pupae (4 and 7 days) after exposure to 0°C for 16 days. The lethal time for 50% survival (LT₅₀) increased with increasing age of pupae. LT₅₀ for 4-day-old pupae exposed to 0°C was 52.1 days. Analysis of mean temperatures at several localities indicated that L. chinensis is able to overwinter outdoors in southern regions, but is unable to overwinter in open fields in northern regions of Japan, suggesting that overwintering in these regions would only occur in greenhouses.     

Effect of temperature on predation of Chilocorus bipustulatus L. (Col.: Coccinellidae) feeding on Agonoscena pistaciae (Hem.: Psyllidae)

Chilocorus bipustulatus L. (Col.: Coccinellidae) is a predatory coccinellid with a wide geographical distribution. Biological control programs should have a good understanding of the capacity of a predator to kill the target prey. Therefore, the age-stage specific predation rate and functional response of C. bipustulatus feeding on Agonoscena pistaciae (Hem.: Psyllidae) were studied at 18, 25, and 32 °C (65?±?5%RH and 16 L: 8D) to confirm its potential as a biological control agent of common pistachio psylla. The functional response at 18 and 25 °C were described by type II and type III at 32 °C. The estimated maximum attack rate (T/Th) was at 25 °C. Moreover, the highest net feeding (C₀) was observed at 25 °C (3271.5 psyllids). This laboratory study, thus, suggested that the predatory coccinellid C. bipustulatus reacted to the rise of temperature by enhancing the predation rate on A. pistaciae.

     

The effects of different temperatures and relative humidity on the development,mortality and nymphal predation of <Emphasis Type="BoldItalic">Anthocoris minki</Emphasis>

Mass rearing techniques are a necessity in developing a suitable and economic biological control method. Anthocoris minki Dohrn (Heteroptera: Anthocoridae), which is successfully reared for use in biological control, is a promising indigenous Anthocoris species for biological control of Agonoscena pistaciae Burckhardt and Lauterer (Homoptera: Psyllidae) in pistachio orchards. Development time of nymphal instars, mortality percentage and prey consumption of A. minki fed on Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs were studied at three constant temperatures (20, 25 and 30 ± 1°C) and two relative humidity levels (40 and 65 ± 5%) under laboratory conditions. Temperature and r.h. significantly affected development time and nymphal prey consumption of A. minki. Duration of incubation and total nymphal development time decreased significantly with each increase in temperature. Total nymphal development time of A. minki at 40% and 65% r.h. was 18.6 and 18.6 days at 20°C; 13.7 and 14.6 days at 25°C; and 10.8 and 11.8 days at 30°C, respectively. The shortest nymphal development time and highest nymphal mortality percentage were recorded at 30°C and 40% r.h. The lowest nymphal mortality was 30.1% and 32.1% at 40% and 65% r.h., respectively, at 25°C; the highest nymphal mortality was 51.5% and 52.1% at 20° and 30°C, respectively, and 40% r.h. The highest average number of E. kuehniella eggs consumed was 123.1 at 20°C and 65% r.h., and the lowest was 86.4 at 30°C and 40% r.h. during nymphal development time of A. minki.     

Temperature-dependent development of Agrotis ipsilon (Lepidoptera: Noctuidae) and its stage transition models

The black cut worm Agrotis ipsilon (Hufnagel) is a destructive crop pest worldwide and a typical cut worm damaging plant parts below the soil surface, which requires a thorough phenological prediction of the target stage for proper management. Temperature is an essential factor affecting the phenology and dynamics of insect populations. So, this study was conducted to evaluate the temperature-dependent development of A. ipsilon fed on Kimchi cabbage (Brassica campestris) in a wide range of temperatures (10 to 40 ℃) in the laboratory. The linear and nonlinear relationship between temperature and development rate (1/development time) was analyzed. The lower threshold temperatures (LT) for eggs, larvae, and pupae were estimated to be 12.1 °C, 9.6 °C, and 11.2 °C, respectively, with thermal constants (degree days for development completion) of 31.3, 342.2, and 181.3 DD at each stage, respectively. Additionally, the thermal constant for tracking the phenology of each stage was determined using a common LT of 10.4 ℃: 40.3 DD for eggs, 315.6 DD for larvae, and 199.6 DD for pupae. Consequently, we provided newly the stage transition models for all stages of A. ipsilon using two basic components of the nonlinear development rate and distribution models to simulate the proportion of individuals shifted from one stage to the next stage. These models in their current form will be useful for constructing a population model for A. ipsilon in the future. Furthermore, the variation in the development time of A. ipsilon reported in previous studies was discussed using 95% confidence limits of the estimated line of our nonlinear models.

     

Maternal age influence on diapause induction in sexual and asexual Trichogramma brassicae

In this study, the effect of maternal age on prepupae diapause of progeny in sexual (Wolbachia free) and asexual (Wolbachia infected) Trichogramma brassicae was studied at two temperatures. Maternal generation (G₁) of both populations was reared at 10L:14D photoperiod, 14 and 20 °C, separately. Mated females from G₁ were supplied with eggs of Ephestia kuehniella, each 48 h from one day after emergence to death. The tendency to diapause in progeny (G₂) was determined by rearing at 10 °C. According to the results, reproductive modes, maternal temperature and age have significant effect on the mean number of eggs laid by G₁ and the diapause percentage of G₂. Offspring whose maternal generation was reared at 20 °C had higher diapause percentage than those reared at 14 °C. Diapause percentage in sexual population was higher than the asexual, which demonstrates a negative effect of Wolbachia on this process. Wolbachia infection modifies the effect of maternal age on the diapause percentage in the offspring at 20 °C but not at 14 °C. The result can be due to lower Wolbachia density at 14 °C and greater Wolbachia density at 20 °C.     

Plant age and ambient temperature: significant drivers for powdery mildew (Erysiphe cruciferarum) epidemics on oilseed rape (Brassica napus)

Powdery mildew (Erysiphe cruciferarum) is an important disease in oilseed rape crops worldwide, but of sporadic importance in most southern Australian crops. Six Brassica napus cultivars were exposed to E. cruciferarum simultaneously in four plant age cohorts. First symptoms of powdery mildew appeared 9 days after inoculation (dai) on the oldest plants [42 days after seeding (das)], but 44 dai in the youngest plants that were exposed to inoculum from sowing, although final disease severity did not differ with the plant age at exposure. The maximum level of pod peduncle infestation was unaffected by plant age (P = 0.37) or cultivar (P = 0.28). The effect of temperature was also investigated. The development of disease on plants was slower and final severity reduced at a day/night temperature 14/10 °C compared with 22/17 °C. In vitro, maximum growth of germ tubes from conidia of E. cruciferarum was at 15–20 °C and survival of conidia reduced by temperatures >30 °C. The results explain the sporadic nature of powdery mildew outbreaks in winter‐grown oilseed rape in Australia, where slow rates of infection occur when seasonal colder prevailing winter conditions coincide with the presence of younger plants, together curtailing rapid disease development until temperatures increase in late winter/early spring. These results explain why epidemics are most severe in the two warmer cropping regions, viz. the northern agricultural region of Western Australia and New South Wales. This study suggests that with increases in winter temperatures under future climate scenarios, earlier and more severe powdery mildew outbreaks in Australia will be favoured.     

Functional responses of the parasitoid,Ertmocerus longipes Compere (Hym., Aphelinidae) to densities of the whitefly,Aleurotuberculatus takahashi David et Subramaniam (Hom., Aleyrodidae) at different temperatures

The present study dealt with the functional responses of the parasitoid,Eretmocerus longipes Compere (Hym., Aphelinidae) to the densities of the whitefly,Aleurotuberculatus takahashi David et Subramaniam (Hom., Aleurodidae) at different temperatures under the laboratory conditions. The results showed that when the initial densities ofA. takahashi-3rd instar were raised from 10 to 320 ind./leaf, the numbers of parasitized nymphs increased as well, ranging from 7.0 to 23.1 at 20°C, 9.8 to 42.9 at 25°C, 6.7 to 39.9 at 30°C, and 1.8 to 8.3 ind./leaf at 35°C, respectively. The Holling Disk Equation was introduced to build up the models of functional responses. The response curves remained type II, although the numbers of parasitized nymphs were significantly different under different temperatures. The suitable initial densities of the host whitefly for parasitization were about 80 individuals per leaf. A negative relation was observed between the initial densities of the whitefly and the parasitization rates by the parasitoid. An increase in the initial densities ofA. takahashi-3rd instars ranging from 10 to 320 ind./leaf resulted in a decrease in the parasitization rate byE. longipes ranging from 70.0% to 7.2% at 20°C, 98.0% to 13.4% at 25°C, 67.0% to 12.5% at 30°C and 18.0% to 2.6% at 35°C with a value of 0.2877 was significantly smaller than that at 20°C with a vlaue of 1.3354, that at 25°C with a value of 1.6465 and that at 30°C with a value of 1.1199, respectively (p<0.01). The handling time (Th) forE. longipes was 0.1521 at 35°C, significantly longer than 0.0510 at 20°C, 0.0289 at 25°C and 0.0320 at 30°C, respectively (p<0.01). The maximum loading number (K) of the parasitized nymphs with a value of 34.5 ind./leaf at 25°C was similar to that with a value of 31.2 ind./leaf at 30°C, about 1.8 times as high as that with a value of 19.6 ind./leaf at 20°C and 4 times more than that with a value of 6.6 ind./leaf at 35°C. It was suggested that temperature affected the functional response by balancing searching rate and handling time. The optimal temperature range for the functional responses ofE. longipes to the densities ofA. takahashi-3rd instar was 25° to 30°C.     

Investigation on the storage possibilities of <Emphasis Type="Italic">Rhyzobius lophantae</Emphasis> Blaisdell (Coleoptera: Coccinellidae) at different temperatures and periods

Storage of natural enemies at low temperatures has an important role in biological control programs. It is an very critical factor that the stored individuals is used without losing their characters such as longevity, survival, fecundity, etc. In this study, the storage possibilities of Rhyzobius lophantae Blaisdell (Coleoptera: Coccinellidae) adults under low temperatures (4 °C and 12 °C) for four different periods (10, 20, 30 and 40 days) were investigated. The survival rates and life span of adults (male and female), daily and total egg numbers laid by females stored at 4 °C and 12 °C for 10, 20, 30 and 40 days were determined. The survival rates of adults stored at 4 °C for 10 and 20 days were found to be 94.54% and 58.02% respectively. However, no adults stored at 4 °C for 30 and 40 days were observed to survive. The highest survival rate was 88% for the adults stored at 12 °C for 10 days. The average daily laid egg numbers were 12.51 and 9.37, and total egg numbers were 850.30 and 738.30 of adults stored at 4 °C for 10 and 20 days, respectively. The decrease in daily and total egg numbers of females stored at 12 °C was observed with increasing storage period. There was no significant difference in longevities of male and female stored at 4 °C and 12 °C. These results show that short-term storage at low temperatures does not affect certain properties of the predator when compared to 12 °C and storage periods.     

Laboratory shelf-life of oil-formulated conidia of the locust and grasshopper fungal pathogen Metarhizium flavoviridae Gams & Rozsypal,in mixtures with the pyrethroid insecticide lambda-cyhalothrin

The addition of 20 ppm lambda-cyhalothrin pyrethroid insecticide to Metarhizium flavoviridae (Fungi: Deuteromycetes) dry conidia in oil kept germination above 80% for 2 and 12 months at temperatures of approximately 30 and 8°C respectively. At 30°C, conidia in oil alone maintained viability for only a few weeks, but this was doubled at 8°C. Even dry conidia retained good viability for only 5 months at the higher temperature. The extended viability of conidia given by adding the pyrethroid to the oil formulation is regarded as very valuable for areas where the fungus is to be used against locusts and grasshoppers.     

Effect of temperature on development,mortality, fecundity and reproduction of<Emphasis Type="Italic">Tuberolachnus salignus</Emphasis> on weeping willow (<Emphasis Type="Italic">Salix babylonica</Emphasis>) and corkscrew willow (<Emphasis Type="Italic">Salix matsudana</Emphasis>)

The development time, survivorship and reproduction ofTuberolachnus salignus (Gmelin) (Hemiptera: Aphididae) [Lachninae, Lachnini] were studied onSalix babylonica (weeping willow) andSalix matsudana (corkscrew willow) at five constant temperatures (17.5, 20, 22.5, 25 and 27.5°C). The development time of immature stages ofT. salignus ranged from 14.56 days at 17.5°C to 12.50 days at 25°C onS. babylonica, and 16.47 days at 20°C to 12.28 days at 25°C onS. matsudana. The total survivorship of immature stages ofT. salignus varied from 28% to 85% at 22.5 and 17.5°C, respectively, onS. babylonica, and from 13% to 63%, respectively, at 17.5 and 25°C onS. matsudana. The greatest intrinsic rate of increase occurred at 25°C onS. babylonica (0.2691) and also onS. matsudana (0.2607). The mean generation time of the aphid population ranged from 14.15 days at 25°C to 16.24 days at 17.5°C onS. babylonica, and from 14.33°C days at 25°C to 19.86 days at 20°C onS. matsudana. The optimal temperature forS. babylonica growth, development time, reproduction and percent survival was 25°C.     

Effect of apple cultivar and of temperature on the biology and life table parameters of the twospotted spider mite<Emphasis Type="Italic">Tetranychus urticae</Emphasis>

Development duration and reproduction rate of the twospotted spider miteTetranychus urticae Koch (Acarina: Tetranychidae) were studied on five different apple cultivars (‘Amasya’ (local cultivar), ‘Golden Delicious’, ‘Granny Smith’, ‘Starking Delicious’ and ‘Starkrimson Delicious’) at 25°C, 65±10% r.h. and 16:8 L:D. In addition, the same parameters were determined on Golden Delicious leaves at three constant temperatures (20°, 30° and 35°C, 65±10% r.h. and 16:8 L:D) in the laboratory.T. urticae performed better on Granny Smith than on the other cultivars, due mainly to high daily egg production (4.6 eggs/♀/day) and the intrinsic rate of natural increase (r _m , which was 0.243 ♀/♀/day). The lowestr _m was observed on Amasya variety (0.231 ♀/♀/day). Development periods of immature stages ofT. urticae varied from 6.5 to 15.5 days at 35° and 20°C, respectively, for females, and from 5.9 to 14.5 days at 35° and 20°C, respectively, for males. The development thresholds of the eggs and pre-adult stages, respectively, were 10.78° and 8.43°C, and total effective temperatures were 57.80 and 172.41 degree-days. Mean generation time (T _o ) of the population ranged from 9.94 days at 35°C to 25.99 days at 20°C. The net reproduction rate increased from 66.99 ♀/♀ at 20°C to 92.19 ♀/♀ at 25°C, and decreased to 84.34 ♀/♀ at 30°C and to 12.04 ♀/♀ at 35°C. The highest r _m occurred at 30°C (0.302 ♀/♀/day) and the lowest at 20°C (0.161 ♀/♀/day). http://www.phytoparasitica.org posting Dec. 19, 2003.     

Seed germination, seedling establishment and growth patterns of wrinklegrass (Ischaemum rugosum Salisb.)

Several laboratory and glasshouse experiments were conducted to assess seed germination, seedling establishment and growth patterns of wrinklegrass (Ischaemum rugosum Salisb.) influenced by temperature and light regimes, and chemical media. Wrinklegrass was a positively photoblastic species, and seed germination was temperature‐dependent and light‐mediated. Seeds soaked in distilled water for 24 h, or oven‐dried at the respective temperature regimes of 15, 20, 25, 30, 35, or 40°C prior to treatment in distilled water and incubated in darkness, failed to germinate. Likewise, no germination prevailed when the seeds were exposed to similar temperature regimes and treated with 0.2 m KNO₃, 5% H₂O₂ or 0.01 m HNO₃, and incubated under continuous darkness. Seeds treated with 5% H₂O₂ at 30°C, or oven‐dried and treated with 0.01% M HNO₃ at 35°C registered 10 and 20% germination. Approximately 75 and 90% of the light‐exposed seeds for all treatments germinated in the first three and six days at 25°C. No germination occurred at 15°C in the first three days after treatment. Seeds subjected to 40°C for six days after treatment recorded 36% germination. The optimum temperatures for seed germination were 25–30°C. Seed drying and soaking treatments widened the windows of the optimal temperatures for wrinklegrass germination. The acidic media of KNO₃, H₂O₂ or HNO₃ favored seed germination. Less than 5% of seed germination occurred with burial or water inundation at depths exceeding 2 cm. Seed burial or inundation at ≥2 cm depths inhibited seed germination. Seeds sown onto moist paddy soils registered ca. 50% germination. Free‐floating seeds on the water surface registered ca. 98% germination within the first six days after seeding. The mean number of seedlings that survived was inversely proportional to water depths, with close to 100% mortality at the 14 cm depths of inundation. Both plant height and seedling survival were linearly proportional to the amount of root mass of seedlings which penetrated the soil. The weed was a prolific seed producer (ca. 6000 seeds/genet or 18 000 seeds/genet per year). The vegetative and reproductive efforts of each wrinklegrass plant registered values of 0.68 and 0.32, respectively.     

Effects of temperature and leaf age on conidial germination and disease development of powdery mildew on rubber tree

Powdery mildew is an important disease of rubber trees worldwide. To assess the effects of temperature and leaf age on conidial germination and disease development, conidia were inoculated onto rubber tree seedlings with leaves at three phenological stages (copper bronze, colour-changing, and light green) and then incubated at six constant temperatures (10, 15, 20, 25, 30, and 35°C). Leaf age did not affect conidial germination (p = .296) whilst temperature did (p < .0001), although conidia were able to germinate at all tested temperatures. The estimated optimal temperature for conidial germination was 23.2°C. Leaf age, temperature, and their interactions had significant effects on conidial infection and hypha number (p < .0001). At 10 and 35°C, more than 2 and 4 days were needed for infection to complete, respectively, compared to <2, 1, 0.5, and 0.5 days for 15, 20, 25, and 35°C, respectively. Sporulation and mildew symptoms were only observed on those inoculated leaves of all stages at 20 and 25°C, and at the copper bronze stage only at 15°C. The latent period on the copper bronze leaves at 15°C was longer (9 days) than at 20 and 25°C (4 days). The latent period at 20 and 25°C increased from 4 to 7 days as the leaf development stage increased from copper bronze to light green. Therefore, temperature affected germination and postgermination growth of rubber tree powdery mildew, whereas leaf age primarily affected postgermination growth of the pathogen.     

Efficacy of dose-dependent indigenous microbial insecticides against cotton aphid,Aphis gossypii Glover (Homoptera: Aphididae) at various temperature regimes

Strain selection based on temperature may be warranted when choosing an isolate for development as a microbial control agent. To this end, the effects of three temperature regimes, namely 20, 25 and 30°C, on the virulence of four Beauveria and two Metarhizium isolates against the cotton aphid, Aphis gossypii, were investigated under controlled conditions, 65–70% relative humidity, and a photoperiod of 12:12 (light: dark) hours. The isolates did vary significantly in their activities of efficacy over a range of temperatures. The highest mortality and lowest survival times were observed at 25°C for DLCO41 and at 30°C for DLCO87; while mortality decreased and survival time increased at temperatures of 20°C. Besides the tested fungal isolate DLCO87 had the lowest LC₅₀ value (6.84 × 10⁵ conidia mL^?1) at 30°C. The promising result of this study should enable us to conduct further studies to determine the potential use of the fungus as an agent against Aphis gossypii both in greenhouse and under field conditions.     

Arrowleaf sida (Sida rhombifolia) and prickly sida (Sida spinosa): germination and emergence

Maximum arrowleaf sida (Sida rhombifolia L.) germination occurred at 35°C, whereas prickly sida (Sida spinosa L.) germinated to the same extent at 35 or 40°C. Arrowleaf sida germinated better than prickly sida at 20 and 25°C, but did not germinate at 40°C. Less than 50% of seed from both species were viable at 45°C after 21 days of exposure. Both species exhibited more than 75% germination at a range of pH from 5.0 to 8.0. Arrowleaf sida germinated to a greater extent than prickly sida from 0 to —800 kPa, and an osmotic stress of —200 kPa reduced prickly sida germination, whereas —400 kPa was necessary to reduce arrowleaf sida germination. Prickly sida emergence was optimal at a planting depth of 0.5 cm, and declined rapidly at deeper planting depths. However, arrowleaf sida emergence was equivalent at planting depths of 0.5–2.0 cm, with declining emergence below 2.0 cm. Neither species emerged from depths exceeding 5.0 cm. Light did not influence the germination of arrowleaf sida or prickly sida. Sida rhombifolia et Sida spinosa: germination et levee Le maximum du germination pour Sida rhombifolia L. a été atteint à 35°C tandis que Sida spinosa L. a germé de facon équivalente à 35 ou 40°C. S. rhombifolia a mieux germé que S. spinosaà 20 et 25°C, mais n'a pas germéà 40°C. Moins de 20% de graines des deux espèces étaient encore viables à 45°C après 21 jours dèxposition. Les deux especes ont germéà plus de 75% dans des niveaux de pH allant de 5 à 8. S. rhombifolia a mieux germe que S. spinosa de 0 à 800 kPa, et un stress osmotique de —200 kPa a réduit la germination de S. spinosa, tandis que —400 kPa ont été nécessaires pour réquire la germination de S. rhombifolia. La levée de S. spinosaétait optimale à une profondeur de semis de 0,5 cm, et décroissait rapidement à des profondeurs plus élevées. Cependant la levée de S. rhombifoliaétait équivalente pour des profondeurs de 0,5 à 2 cm, avec une baisse à partir de 2 cm. Aucune des deux espèces n'a levéà des profondeurs supérieurs à 5 cm. La lumière n'a pas d'influence sur la germination des 2 espèces. Keimung und Auflaufen der Sidafaserpflanze (Sida rhombifolia L.) und der Stacheligen Samtmalve (Sida spinosa L.) Die stärkste Keimung lag bei der Sidafaserpflanze (Sida rhombifolia L.) bei 35 °C vor, während Samen der Stacheligen Samtmalve (Sida spinosa L.) bei 35 oder 40 °C gleich gut keimten. Samen der Sidafaserpflanze keimten bei 20 und 25 °C besser als die der Stacheligen Samtmalve, keimten jedoch nicht bei 40 °C. Nach Lagerung bei 45 °C für 21 Tage waren die Samen beider Arten zu < 20% keimfähig. Bei pH-Werten zwischen 5 und 8 keimten beide Arten zu >75%. Bei osmotischen Drücken zwischen 0 und —800 kPa keimte die Sidafaserpflanze besser als die Stachelige Samtmalve, deren Keimung ab —200 kPa gehemmt wurde, wahrend bei der Sidafaserpflanze —400 kPa erforderlich waren, die Keimung zu verringern. Samen der Stacheligen Samtmalve keimten am besten in 0,5 cm Tiefe, in gröβerer Ablagetiefe schnell schlechter. Bei der Sidafaserpflanze jedoch waren Aussaattiefen zwischen 0,5 und 2,0 cm gleich gut, erst bei Tiefen unter 2 cm ging der Auflauf zurück. Aus Tiefen unter 5 cm keimte keine der beiden Arten. Durch Licht wurde die Keimung der beiden Sida Arten nicht beeinflußt.