Relationships between parasitism,bumblebee foraging behaviour,and pollination service to Trifolium pratense flowers

1. Parasite effects on host behaviour frequently alter their hosts' trophic interactions. There are many compelling examples of such effects in herbivore‐based trophic interactions, but less attention has been paid to how parasite effects on host behaviour can alter mutualistic interactions. 2. Pollination mutualisms depend greatly on pollinator behaviour, and many pollinators are attacked by a wide range of parasites and parasitoids. 3. To investigate whether parasites affect pollination service via changes in host behaviour, natural variation in conopid fly parasitism was used to investigate the relationship between infection and Bombus impatiens Cresson behaviour foraging on arrays of Trifolium pretense L. flowers in the laboratory. The consequences of infection for seed set and seed mass were also examined. 4. Conopid parasitism was not related to any measured behavioural response; however, flowers visited by conopid‐parasitised bees set significantly heavier seeds than those visited by unparasitised bees. Larger bees were more likely to be parasitised, but the relationship between parasitism and seed set still held after accounting for body size. 5. The present results demonstrate that parasitoids may have positive impacts on per‐visit pollination, but, because larger bees were more frequently parasitised, parasitism could also affect pollination by removing the largest pollinators from the population.     

Allele Polymorphism of the Serotonin Transporter Gene and Clinical Heterogeneity of Depressions

Depression disorders are a clinically heterogeneous disease group. Their development is to a substantial extent underlain by dysfunction of the serotonin system, in particular, disturbed serotonin transport. The heterogeneity of depressions is associated, among other factors, with the age at disease onset. Allele polymorphism of the serotonin transporter (5-HTT) gene was tested for association with age at disease onset, clinical signs, and anxiety-related traits of depression patients. A sample included 77 patients (mean age 61.2 ± 8.8 years) with late-onset depression (LOD, mean age at onset 56.58 ± 9.7 years) and 74 patients (mean age 31.0 ± 11.8 years) with early-onset depression (EOD, mean age at onset 23.9 ± 7.4 years). In genotype frequency distribution of two 5-HTT gene polymorphisms, the LOD and EOD groups did not differ from each other (² = 0.33, P = 0.85 for VNTR; ² = 3.33, P = 0.19 for HTTLPR) and from a control group (² = 0.34,P = 0.84 for VNTR; ² = 2.1, P= 0.35 for HTTLPR). In either group, patients differing in VNTR and HTTLPR genotypes did not differ in psychological traits and, in particular, in anxiety-related traits. In the case of the HTTLPR polymorphism, LOD patients with genotype sstended to display less severe neuroticism (t= 2.03, P = 0.0507) and scored significantly less on the Hamilton depression scale (t = 2.19, P = 0.039). Thus, the 5-HTT gene polymorphisms do not affect the risk of depression but is possibly associated with specific clinical signs of the disease, at least in elderly patients.     

Style morph frequencies in Minnesota populations of Lythrum (Lythraceae)

Style morph frequencies (shortmidlong) were determined for a total of n = 11 918 plants in 16 Minnesota populations of Lythrum salicaria L. Nine populations were in the establishment phase, with population sizes ranging from n = 56 to n = 2 192. Most of these populations exceeded previously reported population sizes in the native European habitat. A nonparametric statistical test, the chi-square (²), can be used to determine if populations are at isoplethic equilibrium (111, shortmidlong); a ² value >5.99 is significant at the 5% level. Only one established population (White Bear Lake, n = 1991, ² = 3.0) fitted the null hypothesis for isoplethy, although all established populations contained all three style morphs. Pooled values for these populations indicated an excess of mids and longs, with shorts being deficient. Colonizing populations had a higher percentage of mids (54%) when compared to established populations (33.7%). Short styles were almost nonexistent (8%) in colonizing populations. Five out of the seven populations lacked at least one style morph. A review of the literature reporting style morph frequencies in tristylous L. salicaria revealed that no statistical analysis for isoplethy has been performed. Darwin originally assumed that all populations would be isoplethic, possessing equal numbers of all three style morphs, but concluded, without statistical analysis, that, instead, populations were anisoplethic. Since tests for statistical deviations from the expected frequencies (111) have not been used, ² analysis was performed. Several of these populations were at isoplethic equilibrium (Nadder su2 = 1.7, Blelham ² = 1.69, Potsdam ² = 1.5, Vestfold ² = 0.4, Buskerud ² = 5.62, Kilchberg ² = 0.35, Lausanne ² = 3.32, Canberra ² = 5.29, Massachusetts ² = 3.13), suggesting that the general conclusion of anisoplethy in tristylous L. salicaria is inappropriate.This is Scientific Journal Series Paper Number 19 128 of the Minnesota Agricultural Experiment Station     

Correlation between antibodies to Cowdria ruminantium (Rickettsiales) in cattle and the distribution of Amblyomma vector ticks in Zimbabwe

Cowdriosis, caused by Cowdria ruminantium, is transmitted by Amblyomma ticks, which are widely distributed in Zimbabwe. To assess the distribution of this disease in Zimbabwe, cattle either exposed to Amblyomma ticks or maintained in areas free from these ticks were tested for antibodies to Cowdria. A total of 324 sera were tested using competitive ELISA and the indirect fluorescent antibody test (IFAT). At diptanks in Amblyomma-infested areas 52% (n=95) and 26% (n=47) of sera were positive by cELISA and IFAT, respectively. At diptanks in Amblyomma-free areas 11% (n=125) and 10% (n=134) of sera were positive by cELISA and IFAT, respectively. The results were significantly different between Amblyomma-infested and tick-free areas (²=24.73, P0.005 for IFAT and ²=57.53, P0.005 for cELISA). High background readings in field sera, possibly due to cross-reactive antibodies to Ehrlichia spp., complicated the determination of a realistic cut-off point, especially in cELISA. On the basis of the distribution of Amblyomma ticks, currently a large part of Zimbabwe can be considered endemic for the disease.     

Larval development of two parasitic flies (Conopidae) in the common host Bombus pascuorum

Abstract.

• 1 Whenever parasitism by more than one female occurs, larvae of parasitoids not only have to resist host defence but also face competition with other (unrelated) larvae. Competition is particularly important in solitary parasitoids where only one larva is able to complete its development. Such a situation is found in Conopidae (Diptera) parasitizing adult bumble bees where larvae of two species of conopid flies, Sicus ferrugineus L. and Physocephala rufipes F. often compete within the common host Bombus pascuorum Scopoli. This study analysed the larval development of the two species and asks how competition among larvae may be regulated.
• 2 Parasitized workers of B.pascuorum were caught in the field and kept according to different experimental schedules in the laboratory. This provided stage-structured data for the temporal course of development of the parasitic larvae. For the analysis, a simulation model was constructed that estimated the duration of all parasitic stages (Manly, 1990, first method). In both species the egg stage was found to be approximately 2 days, first instar 3 days, second instar 4 days, and third instar 3 days. The total development time is an estimated 10.8 days from oviposition in S.ferrugineus and 11.4 days in P.rufipes. S.ferrugineus develops faster in the beginning, probably because of its larger egg size, whereas P.rufipes pupates at larger size. First-instar larvae of both species possess strong, pointed mandibles.
• 3 The success of conopid larvae seems only marginally affected by host defence, for a single larva per host almost always completes development. Under competition, however, mortality rate increases substantially, and most larvae die in their first instar. Moreover, they show signs of melanization. The estimates for developmental times and the patterns found in this study suggest that conopid larvae seem capable of physical attacks, particularly during the first instar, when elimination of competitors is most common, and that S.ferrugineus has a time advantage because of its faster early development. Because most studies have previously been carried out with hymenopteran parasitoids, this study provides new information about the other large group of parasitoid insects, the Diptera, and demonstrates convergent patterns.

     

Patterns of parasite infection in bumble bees (Bombus spp.) of Northern Virginia

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Patterns of parasitism among conopid flies parasitizing bumblebees

The effects of host size and host species on the prevalence and fitness of conopid flies (Diptera: Conopidae) parasitizing bumblebees (Hymenoptera: Apidae) were investigated. Field data from nine sites across south‐western Alberta, Canada, showed that conopids parasitized, on average, 12.3% of workers and 3.5% of male bees. In general, bee mass was a better predictor of host use and conopid offspring size than bee species. Host mass could not, however, explain the very low prevalence of conopids in the long‐tongued bumblebee, Bombus californicus Smith, or in male bees in general. Conopids predominately infested bees of intermediate size, and as a result, occurred most commonly in the intermediately sized species, B. flavifrons Cresson. Host quality, in terms of conopid offspring size, increased as a non‐linear function of bee size. The results are discussed with respect to the impact of conopids on bumblebee populations, and the relation between host quality and patterns of host use.     

Analysis of the Pectin Methylesterase Activity in a Segregating Population of a Tobacco Transgenic Plant using Callus Tissue

With the aim to develop a callus-based tool to study the activity of transgenes, we induced callus from a segregating population of a tobacco transgenic plant expressing a single copy of a transgene designed to overexpress a pectin methylesterase isoenzyme (pmeu1). Pectin methylesterase (PME) activity in the whole plant showed 4-fold induction whereas in callus tissue we found up to 20-fold induction. Furthermore, determination of PME activity of 38 segregating transgenic calluses showed the presence of four groups: calluses with activity like control (calluses-c), calluses with 5-fold induction (calluses-5); calluses with 10-fold induction (calluses-10) and calluses with 20-fold induction (calluses-20) of PME activity. Based on the expected Mendelian segregation of azygous:hemizygous:homozygous, we placed calluses-c, calluses-10 and calluses-20 as azygous, hemizygous and homozygous, respectively. This is a behavior that can be explained by the gene-dosage phenomena. Chi-square statistics was used to test whether the calluses-5 are azygous (²= 4.24) or either homozygous or heterozygous (²= 0.034). The Chi-square critical value is ² _{(=0.05, 1 df)}= 3.84 which allowed to conclude that calluses-5 are either homozygous or heterozygous. Next, we tested whether calluses-5 are either hemizygous (²= 6.36) or homozygous (²= 0.314). The critical value of ² _{(=0.05, 2 df)}= 5.99 was highly significant for concluding that calluses-5 are homozygous for the transgene. This is a behavior that can be explained by the co-silencing phenomena. It is concluded that the use of callus tissue can allowed to find changes in expression of transgenes that are difficult to observe in the whole plant.     

Field evidence that host selection by conopid parasitoids is related to host body size

Summary The body size of the host insect in which a parasitoid develops can have important effects on its development and life history. Large and small host body size have both been suggested to be advantageous to parasitoids, depending on the life-history of the species concerned. We test field data on the bumblebeeBombus terrestris and its conopid parasitoids for evidence of differences in size between parasitised and unparasitised worker bees. Bees acting as hosts for conopid parasitoids are on average larger-bodied than unparasitised bees. This result holds for bees collected in two different years, and whether bees are collected while foraging or from the nest. The results we present demonstrate differential parasitism of hosts of different body sizes, but do not necessarily indicate active host choice by conopids. However, they are in agreement with independent evidence that conopids develop more successfully in large-than in small-bodied hosts.     

The effects of landscape on bumblebees to ensure crop pollination in the highland agricultural ecosystems in China

Honey bees and wild bees provide critical pollination services to agricultural ecosystems; however, the relative contributions of different bee taxa are not well understood. The natural habitats surrounding farmland support food and nesting resources for wild bees and therefore play an important role in the maintenance of crop pollination. In this study, we selected Cucurbita pepo L. (squash) as a model crop to investigate the relative importance of honey bees and bumblebees in pollinating the crop. Thirteen fields, which were surrounded by a gradient of natural habitat, were investigated on the Yunnan‐Guizhou Plateau in China. We measured the visit densities of honey bees and bumblebees, the number of pollen grains deposited in a single visit by the two bee taxa, as well as the overall pollen grains deposited on stigmas during a flowering day, and then used Bayesian inference to decouple the pollen grains deposited by either the honey bees or the bumblebees. Compared with honey bees, bumblebees deposited a higher number of pollen grains on stigmas in a single visit, but had a lower visit density than honey bees. Meanwhile, the bumblebee visit density increased along the proportion of natural habitat, while the honey bee visit density was not affected by the surrounding natural habitat. Data simulations using Bayesian inference showed that on a flowering day, the number of pollen grains deposited by bumblebees increased with the proportion of natural habitat in the surrounding landscape, but the number of pollen grains deposited by honey bees did not. Moreover, the total numbers of pollen grains deposited by honey bees or bumblebees alone were all below 2000 (the critical level to satisfy the pollination requirement of this crop). Pollen calculations demonstrated that the number of pollen grains deposited by the two bee taxa was greater than 2000 in fields surrounded by more than 13% natural habitat (grasslands and forests). The results revealed that bumblebees ensured C. pepo pollination in combination with honey bees in the highland agricultural ecosystems.     

Regional Differentiation in the Dynamics of the Pollen Seasons of Alnus, Corylus and Fraxinus in Poland (Preliminary Results)

In 1995–1996 a study of pollen concentrations of Corylus, Alnus and Fraxinus was performed at seven sites in regions of different climatic and natural conditions. The aim of the study was to determine whether regional differences in the course and duration of pollen seasons occur in Poland. The study was performed using a volumetric method. Several phases during the pollen season were defined for each taxon (1, 2.5, 5, 25, 50, 75, 95, 97.5, 99% of annual total) and duration of the pollen seasons was calculated using 98 and 90% methods. Dynamics and duration of the pollen seasons and a start of particular phases of the season were compared among sites. On the basis of the preliminary analysis it could be supposed that regional differences were most evident in the case of Corylus. The pollen season of this taxon started the earliest in Pozna where thermal conditions were most favourable and the latest in Gdask, a place at the furthest to the north ( ², 0.05). In montane regions (Zakopane, Rabka) last phases of the season were significant extended ( ², 0.05). Probably it results from secondary pollen deposition and a long-distance transport by montane wind. In case of Fraxinus the significant regional differences in the start of the pollen season were not found. The study supported that weather conditions have the substantial influence on the start of consecutive phases of the pollen season.     

Genetic Determinants of Predisposition to Bronchial Asthma

The ratio between the normal (+) and null (0) alleles of the genes encoding glutatione S-transferases M1 (GSTM1) and T1 (GSTT1) were studied in normal individuals from northwestern Russia (control group) and in patients with bronchial asthma (BA). The frequency of the GSTM1 0/0 genotype in the population sample was statistically significantly lower (37.8%) than in the BA patients (82.1%; ² = 16.8;P< 0.001; _W² = 15.7; = 0.01). For the GSTT1 gene, similar data were obtained. The frequency of the GSTT1 0/0 genotype in healthy donors was statistically significantly higher (16.3%) than in the BA patients (73.7%; ² = 28.5;P < 0.001; _W² = 23.22; = 0.01). A significant preponderance of the compound homozygotes for the GSTM1 and GSTT1 null alleles among the BA patients was observed. The frequency of the GSTM1 0/0, GSTT10/0 individuals among the patients was 57.9%, while it was only 4.7% among the controls (² = 27.4; P < 0.001).     

Effect of osmotic gradient on ADH-induced intramembranous particle aggregates in toad bladder

Summary Paired toad urinary bladders were prepared without or with an osmotic gradient (175 mosm) across them, stimulated for 2.5 (n=6), 5 (n=6), 30 (n=6) or 60 (n=6) min with ADH (20 mU/ml), and studied by freeze-fracture electron microscopy. Water permeability at these times was assessed in additional bladders (n=6 for each case) after tissue fixation according to the technique of Eggena. After both 60 and 30 min of ADH stimulation, the presence of a gradient compared with the absence of one was associated with fewer aggregates (242±35vs. 382±14 ×235 m^–2 at 60 min,P<0.01; 279±36vs. 470±51 ×235 m^–2 at 30 min,P<0.01) and lower water permeability (8.4±1.1vs. 18.8±1.8g×min^–1×cm^–1 ×mosm ^–1 at60min,P<0.005; 9.2±1.0vs. 22.0±2.1 g ×min^–1×cm^–2×mosm ^–1 at 30 min,P<0.001). In addition, with a gradient both maximum water permeability and maximum aggregate frequency were reached nearly together; a similar correspondence occurred without a gradient. We conclude that in the presence of an osmotic gradient both the ADH-associated aggregates and the water permeability response to ADH are prevented from reaching the higher levels observed in bladders not exposed to a gradient.     

No evidence for linkage disequilibrium between Bf and GLO in African Negroids

Summary A sample of South African Negroids (n=791) was scored for each individual's Bf and GLO phenotype. (The genes for the Bf and GLO polymorphisms are included in a known cluster of linked genes on chromosome 6.) Following a ²-test the respective two series of alleles were found to be distributed at random, i.e., there was no evidence for a linkage disequilibrium. This result is discussed in terms of the linkage relationships and map distances of the genetic markers involved.Supported by the Deutsche Forschungsgemeinschaft (DFG), Bonn-Bad GodesbergSupported by a grant from the Georg and Agnes Blumenthal-Stiftung, BerlinSupported by a research fellowship (1975/76) awarded by the Alexander von Humboldt-Stiftung, Bonn-Bad Godesberg     

Instar-specific head and body lengths of Hyalella(Amphipoda): criteria for starting and endpoints in experimental studies

Abstract Instar-specific data on head length and body length of Hyalella azteca was obtained from live specimens reared individually at 23 ± 1 °C under a 14L:10D photoperiod and with food ad lib. Both head length and body length were strong predictors of instar number through instars 1 – 10. The relationship between instar number and head length was linear (head length [m] = 104.28 + 61.05[instar]; r ²=0.98, P<0.001), whereas that between instar and body length was not (body length [m] = 1339.28 + 55.82[instar]²; r ² = 0.97 , P< 0.001). Head length measurements were easier to obtain and were more accurate than body measurements. Both measurements can be obtained without injury to the animal, permitting repeated observations on the same individual.     

Polymorphisms at the GLUT1 (HepG2) and GLUT4 (muscle/adipocyte) glucose transporter genes and non-insulin-dependent diabetes mellitus (NIDDM)

Summary In order to determine the possible contribution of the GLUT1 (HepG2) glucose transporter gene to the inheritance of non-insulin-dependent diabetes mellitus (NIDDM), two restriction fragment length polymorphisms (RFLPs) and the related haplotypes at this locus were studied in 48 Italian diabetic patients and 58 normal subjects. Genotype frequencies for the XbaI polymorphism were significantly different between patients and controls (XbaI: ² = 9.80, df= 2, P < 0.0079). A significant difference was also found in the allele frequencies between NIDDM patients and controls (² =9.39, df = 1, P < 0.0022), whereas no differences were found for the StuI RFLP. No linkage disequilibrium was detected between the XbaI and StuI RFLPs in this sample. The analysis of the four haplotype frequencies (X1S1, X1S2, X2S1, X2S2) revealed a significant difference between diabetic patients and controls (² = 14.26, df =3, P < 0.002). By comparing single haplotype frequencies, a significant difference between the two groups was found for the X1S1 and X2S2 haplotypes. A two-allele RFLP at the GLUT4 (muscle/adipocyte) glucose transporter gene, detected with the restriction enzyme KpnI, was also examined; no differences were found between patients and controls for this RFLP. The finding of an association between polymorphic markers at the GLUT1 transporter and NIDDM suggests that this locus may contribute to the inherited susceptibility to the disease in this Italian population.     

The influence of two endoparasitic wasps, <Emphasis Type="Italic">Hyposoter didymator</Emphasis> and <Emphasis Type="Italic">Chelonus inanitus</Emphasis>, on the growth and food consumption of their host larva <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>

The influence of parasitism by Hyposoter didymator (Thunberg; Hymenoptera: Ichneumonidae) and Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) on the growth and food consumption of their host Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) was studied in the laboratory. Parasitised larvae consumed significantly less artificial diet than unparasitised ones. Egg parasitisation by C. inanitus affected host larval consumption from the second day after emergence and it was significantly different from that of unparasitised ones. H. didymator, however, started to reduce larval consumption 4 days after parasitisation on the third instar host larvae. The overall reduction achieved by the larval endoparasitoid H. didymator is higher than that caused by the egg-larval endoparasitoid C. inanitus. The final body weight of a parasitised host larva by H. didymator and C. inanitus was only 6.7 and 13.0% of the maximum weight of an unparasitised sixth instar larva respectively. Moreover, parasitised larvae never reached the last instar. Results indicated that parasitised larvae might cause considerable less damage to the host plant than unparasitised ones.     

Elevated frequency of an ETS-1 restriction fragment polymorphism in chronic B-cell leukaemia

We studied the frequency of an SstI polymorphism in 70 patients with chronic B-cell leukaemia (CLL) and 100 normal controls. There was a highly significant difference in the distribution of the three genotypes between the CLL patients and the normal controls (²= 13.46, 2 df, P<0.001). The C2 allele was found more frequently in CLL patients and may be a marker for a predisposition to develop CLL.     

Contrasting frequencies of parasitism and host mortality among phorid and conopid parasitoids of bumble-bees

Abstract 1. Phorid (Diptera, Phoridae) and conopid (Diptera, Conopidae) parasitism among four North American bumble-bee (Hymenoptera, Apidae) species was investigated. Male bumble-bees experienced a significantly higher incidence of parasitism by the phorid, Apocephalus borealis Brues, and a significantly lower incidence of parasitism by the conopid, Physocephala texana Williston, than did workers.
2. The incidence of parasitism by A. borealis and P. texana varied between bumble-bee sexes and species in patterns that did not reflect differences in relative host abundance. Differences in foraging behaviour between bumble-bee workers and males, as well as between species, may explain these results.
3. Bumble-bee workers and males parasitised by A. borealis had significantly shorter lifespans than unparasitised bees. Based on previous estimates of bumble-bee mortality, A. borealis parasitism may reduce worker lifespans by up to 70%. In contrast, the mortality rate of bees parasitised by P. texana was not significantly different from that of unparasitised bees.
4. These results contrast with previous work highlighting the importance of conopid parasitism to bumble-bee populations, and suggest that phorid parasitism may impose greater costs to bumble-bees than does conopid parasitism in local populations.     

Einfluß von Bromuracil auf die Mutationsauslösung und Inaktivierung durch UV und Röntgenstrahlen beim Phagen χ

Zusammenfassung Durch Anreicherung in BUdR- und FUdR-haltigem Medium wurde in die DNS des Serratiaphagen Bromuracil (BU) eingebaut. Im CsCl-Gradienten zeigte die Dichte der BU--Partikel einen Ersatz des Thymins durch BU von 25 bis 30% an. Die Häufigkeit zweier Plaquetypmutanten (c und b) war in der BU--Population signifikant (durchschnittlich 1,4 bzw. 2,4), die des dritten Typs (e) nur insignifikant über die in BU-freien Phagen erhöht. Im Vergleich zu letzterem betrug die absolute Häufigkeit der zusätzlichen c- und b-Mutanten in BU- 2,2 × 10^–4 bzw. 1,1 × 10^–4.Die UV-Inaktivierung von BU- war etwa um den Faktor 1,40 höher als die des normalen . Die Inaktivierung durch Röntgenstrahlen war dagegen nur um das 1,14fache erhöht. Die Häufigkeit der durch Röntgenstrahlen induzierten Plaquemutationen wurde durch den BU-Einbau nicht merklich beeinflußt. Dagegen war die UV-Induktion der Mutationen sehr viel mehr verstärkt als die UV-Inaktivierung. Die Sensibilisierungsfaktoren der drei Mutantentypen waren verschieden und am höchsten bei niederen UV-Dosen (3,4, 5,0 und 22 für c, b bzw. e). Das bedeutet eine Annäherung der Dosiskurven an linearen Verlauf. Die zur Auslösung von Mutationen erforderliche Trefferzahl wird somit durch BU-Einbau vermindert. Für -normal entsprachen die Kurven der UV-Mutationsinduktion dem 2-Treffertyp. Es wird geschlossen, daß die Hemmung der Dunkelreaktivierung (HCR) der Letalläsionen und Prämutationen in BU-DNA nicht die einzige Ursache für die Unterschiede in den UV-Sensibilitäten ist, sondern daß die Bildung anderer UV-Produkte als in der normalen DNA ebenfalls eine Rolle spielt.

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Summary Bromouracil (BU) was incorporated into the DNA of theSerratiaphage by means of culture in a medium with BUdR and FUdR. The density of BU-x particles in the CsCl-gradient indicated a replacement of about 24 to 32 % of the thymine by BU. The frequency of two types of plaquemutants (c and b) in the BU--population was increased significantly above the frequencies in BU-free phage by average factors of 1.4 and 2.4, resp. A third mutant type (e) was increased less. The absolut frequencies of additional c- and b-mutants in BU- compared with normal were about 2.10^–4 and 1.10^–4, resp.The UV-inactivation of BU- was higher by a factor of about 1.40 than that of normal , the inactivation by X-rays was only 1.14 times higher. The X-ray induced plaquemutation frequencies were not remarkably influenced by incorporated BU, but UV-mutation-induetion was increased much stronger than UV-inactivation. The sensitization factors were different for the three mutation types and highest at low UV-doses (3.4, 5.0 and 22 for c, b and e resp.). The UV-dose curves of mutation induction in normal are of the 2 hit type, but for BU- they were significantly less curved indicating the participation of 1-hit-processes in premutation production. It is concluded that inhibition of dark repair (HCR) of lethal lesions and premutations in BU-DNA is not the only reason for the differences in UV-sensitivities but that production of other species of UV-products in BU-DNA than in normal DNA plays also a role.