Larvae Of Different Ages Research Articles

A substance in honey bee larvae inhibits the growth of Paenibacillus larvae larvae

Paenibacillus larvae larvae, a Gram-positive and spore-forming bacterium, is the cause of American foulbrood. We investigated the resistance of larvae of different ages from different colonies against P. larvae larvae. We prepared ethanol-water-extracts from two, three, four and five day old larvae and also larvae in two capped stages to test the ability of the homogenates to inhibit the growth of P. larvae larvae in vitro. There were age and colony dependent differences in the inhibiting potentials of larvae. The results suggest that the concentration of the inhibiting substance(s) in the extract might be responsible for the known different degree of resistance against P. larvae larvae in vivo. Our results further show that the extracts of the two-, three- and four-day-old larvae have the ability to inhibit the growth of P. larvae larvae very well, while starting around day five the inhibiting effect is gradually reduced. Apis mellifera carnica / Paenibacillus larvae larvae / honeybee larvae / age-related resistance /

Flutuação populacional e intensidade de infestação da broca-dos-frutos em cupuaçu

Dentre as pragas do cupuaçueiro Theobroma grandiflorum (Wild. ex Spreng.) Schum., a broca-dos-frutos, Conotrachelus humeropictus Fiedler (Coleoptera: Curculionidae), é a mais importante, devido aos danos causados e por estar disseminada em alguns Estados da região Norte do Brasil. Os objetivos deste trabalho foram avaliar a flutuação populacional de adultos de C. humeropictus, determinar a intensidade de infestação e caracterizar o ataque de larvas desta praga em frutos de cupuaçueiros, em sistemas agroflorestais no Estado de Rondônia. Para obter a flutuação populacional de adultos da broca, foram amostradas semanalmente, durante o período de março/98 a julho/00, 20 plantas de cupuaçu, pelo método do sacolejo, em duas áreas de agrossilvicultores. A avaliação da população de larvas foi realizada durante duas safras, onde foram coletados e abertos frutos atacados pela broca. A determinação da infestação da praga foi obtida através da porcentagem de frutos broqueados. Adultos de C. humeropictus ocorrem durante todo ano nas plantas de cupuaçu, na área estudada, mas predominam na floração, início da frutificação e durante o período de safra. Tanto os frutos verdes como os maduros são atacados, sendo que larvas de idades diferentes podem ocorrem em um mesmo fruto. Perdas superiores a 50% na produção de frutos, devido ao ataque da broca, ressaltam a importância desta praga na região.

Toxicity, feeding deterrence, and effect of activity of 1,8-cineole from Artemisia annua on progeny production of Tribolium castanaeum (Coleoptera: Tenebrionidae).

1,8-Cineole isolated from Artemisia annua was tested against Tribolium castaneum (Herbst) for contact toxicity, fumigant toxicity, and antifeedant activity. The adults of T. castaneum were more susceptible than larvae to both contact and fumigant toxicity of 1,8-cineole, and LD50 and LC50 values of 108.4 microg/mg body weight of adult insect and 1.52 mg/liter air were found, respectively. Furthermore, 14-d-old T. castaneum larvae were more tolerant than 16- and 18-d-old larvae and adults to the contact toxicity of 1,8-cineole, but the 16- and 18-d-old larvae have similar susceptibility. In contrast, all the larvae (14-18 d old) of T. castaneum were much more tolerant than the adults to the fumigant action, but larvae of different ages had similar susceptibility. The compound 1,8-ciineole applied to filter paper at a concentration of 3.22-16.10 mg/cm2 significantly (P < 0.05) reduced the hatching of T. castaneum eggs and the subsequent survival rate of the larvae. Adult emergence was also reduced by 1,8-cineole. Feeding deterrence of 81.9% was achieved in T. castateum adults by using a concentration of 121.9 mg/g food, whereas larvae showed 68.8% at the same concentration.

Cloning and developmental expression of a family of pleurocidin-like antimicrobial peptides from winter flounder, Pleuronectes americanus (Walbaum)

Low molecular weight antimicrobial peptides are an important component of the innate immune system in animals, yet they have not been examined widely in fish. Of particular interest is their expression during development and in response to environmental conditions and disease. Here, we report the isolation of four genomic sequences encoding putative antimicrobial peptides from the winter flounder, Pleuronectes americanus (Walbaum), as well as reverse transcription-PCR products from two tissues that form the first defensive barrier to microbes — skin and intestine. Alignment of the predicted polypeptide sequences shows a conserved hydrophobic signal peptide of 22 amino acids followed by 25 amino acids that are identical (WF2) or homologous to the amino acid sequence of pleurocidin, followed by a conserved acidic portion. Southern hybridisation analysis indicates that related peptides are encoded in the genomes of other flatfish species. Northern and RT-PCR analyses of RNA from multiple tissues show that two of the pleurocidin genes are expressed predominantly in the skin whereas two other genes are expressed mainly in the intestine. RT-PCR assays of total RNA from larvae of different ages provide the first evidence of developmental expression of antimicrobial peptides in fish and indicate that the pleurocidin gene is first expressed at 13 days post-hatch in winter flounder.

Development of the solitary larval endoparasitoid Glyptapanteles porthetriae (Hymenoptera: Braconidae) in its host Lymantria dispar (Lepidoptera: Lymantriidae)

The development of the solitary endoparasitic braconid Glyptapanteles porthetriae in gypsy moth larvae of different ages was studied. Host larvae were parasitized during the premolt to the 2nd instar (A-larvae), to the 3rd instar (B-larvae) or to the 4th instar (C-larvae), respectively. The percentage of successfully parasitized larvae decreased markedly with the age of the host at the time of parasitization. When parasitization occurred at the premolt to the second or third instar, parasitoid larvae successfully emerged at rates of 68% and 57%, respectively, in contrast to the 17% from larvae parasitized in the premolt to the fourth instar. In all three groups of parasitized larvae the final host instar was significantly longer than the corresponding instar of unparasitized control larvae of the same age. However, the growth and growth rate of parasitized larvae were reduced compared to control larvae. Due to the extremely low rate of successful development of G. porthetriae in C-larvae, parameters of parasitoid development were only recorded in A and B-host larvae. In both the parasitoid growth was slow during the first instar but rapidly increased during the second instar. Total developmental time of the parasitoid was significantly longer in B-host larvae, and the resultant cocoons were heavier than those that developed in A-host larvae, but proportionally fewer of the offspring were females. Within both groups the female wasps took significantly longer to develop than the males.

Racing against host's immunity defenses: a likely strategy for passive evasion of encapsulation in Asobara tabida parasitoids

The hymenopteran Asobara tabida Nees (Braconidae, Alysiinae) develops as a solitary endophagous parasite in larvae of several Drosophila species. Most A. tabida eggs possess a sticky chorion which attaches to the tissue of the host organs within a few hours following oviposition. A. tabida sticky eggs usually avoid encapsulation, though the probability of survival decreases in hosts carrying a larger number of circulating hemocytes. Here, we hypothesized that the elicitation of the encapsulation reaction may result from a race between two phenomena: the host's hemocytic reaction and the embedment of the parasitic egg within the host tissues. In order to test this hypothesis, we measured the speed of capsule formation in D. melanogaster larvae of different ages, knowing that the number of circulating hemocytes increases with the age of the larvae. Using a non-virulent A. tabida strain, the eggs of which do not attach to the host tissue, we found that the speed of capsule formation increased correlatively with the age of the D. melanogaster larva. Therefore, the hypothesis of a physiological race between host's immunity defenses and parasite's avoidance of host's defenses is strongly supported by our results. Also, A. tabida eggs which attach to the host's tissue before the attack by the hemocytes has taken place may be considered as a strategy of passive evasion from encapsulation.

Bioactivities of essential oil from Elletaria cardamomum (L.) Maton. to Sitophilus zeamais Motschulsky and : Tribolium castaneum (Herbst)

Contact and fumigant toxicities and antifeedant activity of the essential oil of cardamom, Elletaria cardamomum, to two stored-product insects, Sitophilus zeamais and Tribolium castaneum, were investigated. Topical application was employed for contact toxicity studies, and filter paper impregnation was used for testing fumigant action. The adults of S. zeamais and T. castaneum were equally susceptible to the contact toxicity of the oil at the LD 50 level, with LD 50 values of 56 and 52 μg mg −1 insect respectively. However, S. zeamais was more susceptible than T. castaneum at the LD 95 level. For fumigant toxicity, S. zeamais adults were more than twice as susceptible as T. castaneum adults at both LD 50 and LD 95 levels. Furthermore, 12-day larvae of T. castaneum were more tolerant than the adults to the contact toxicity of the oil, but 14- and 16-day larvae had the same susceptibility as the adults. The susceptibility of the larvae to contact toxicity increased with age. In contrast, all the larvae (12–16 days old) of T. castaneum were much more tolerant than the adults to the fumigant action, and larvae of different ages had similar susceptibility. Cardamom oil applied to filter papers in the concentration range 1.04–2.34 mg cm −2 significantly ( P<0.05) reduced the hatching of T. castaneum eggs and the subsequent survival rate of the larvae. Adult emergence was also drastically reduced by cardamom oil. When applied to rice or wheat, the oil totally suppressed F1 progeny production of both insects at a concentration of 5.3×10 3 ppm. Feeding deterrence studies showed that cardamom oil did not have any growth inhibitory or feeding deterrence effects on either adults or larvae of T. castaneum. However, it significantly reduced all the nutritional indices of the adults of S. zeamais, but with very slight feeding deterrence (27%) at a concentration of 1.44×10 4 ppm.

Juvenile hormone acid and ecdysteroid together induce competence for metamorphosis of the Verson's gland in Manduca sexta

In the last larval instar of Lepidoptera, ecdysteroid in the absence of juvenile hormone (JH) is believed to cause the shift from larval to pupal development. In Manduca sexta, tissues such as the Verson's gland and crochet epidermis become pupally committed before the earliest pulse of ecdysteroid that occurs on day 2. What causes the change in commitment in these tissues? First it was necessary to determine at what stage these tissues become competent to express the pupal program. Last instar larvae of different ages were induced to molt prematurely by feeding the ecdysteroid analog RH5992 and Verson's gland proteins were analyzed by SDS–polyacrylamide gel electrophoresis. Glands became competent to make pupal proteins between 24 and 32 h after the last larval ecdysis. Next, hormonal regulation of competence was examined in ligated abdomens of 12h last instar larvae. Treatment with JH II acid or methoprene acid plus a low dose (1/50th of the molt inducing dose) of RH5992 induced competence, whereas RH5992 alone, methoprene acid alone or methoprene plus RH5992 did not. Verson's glands maintained in vitro produced pupal proteins in response to methoprene acid together with RH5992 but not with RH5992 alone. Likewise, crochet epidermis lost the ability to make crochets (metamorphic change) only in isolated abdomens treated with JH II acid or methoprene acid and low doses of RH5992. In conclusion, JH acid in the presence of basal levels of ecdysteroid induces tissue competence for metamorphosis. Metamorphic competence is followed by commitment, induced by a small pulse of ecdysteroid in the absence of JH, and finally by expression caused by a high titer of ecdysteroid. It is proposed that JH acid is an essential metamorphic hormone.

Trichinella spiralis: the infectivity of synchronous newborn larvae of different ages inoculated intraocularly.

Trichinella spiralis infection results in the transformation of muscle cells into a new, non-muscular cell called the nurse cell, and the nurse cell-muscle larva complex is finally created. To investigate whether T. spiralis infectivity is NBL age-dependent, five groups of synchronous newborn larvae (sNBL) were obtained at 1, 9, 24, 48, and 72 h of age and were inoculated into mice by intravenous injection into the retro-orbital venous plexus. When both "young" groups of sNBL (1 and 9 h old) were injected, the highest number of larvae were capable of infecting the muscle cells. The highest infectivity of 80.0 % was observed for 9-h-old sNBL. In older sNBL the infectivity gradually decreased; thus, for 72-h-old sNBL the lowest level - 0.1% - was detected. Therefore, an "age limit" for NBL infectivity in the present study was precisely determined.

Localization of hatching enzyme in embryos and larvae of the sea-squirt Ciona intestinalis

Summary A polyclonal antibody raised against the hatching enzyme of Ciona intestinalis (D'Aniello et al., 1997) was used on larvae of different ages in whole mount immunofluorescence experiments in order to localize the cells secreting the enzyme. After staining with FITC-conjugated second antibody, the larvae were observed by confocal microscopy. Larvae just before hatching (9–10 hours after fertilization) showed the presence of the enzyme in the peripheral cells of the adhesive papillae. The newly hatched larvae showed fluorescence also in the epidermal cells of the tip of the tail. Higher magnification confocal images of the papillae revealed bright fluorescence both in peripheral cells of the papillae and in the cavity between the tunic and the apex of the papillae (hyaline cap). The swimming larvae maintain the fluorescence in the peripheral cells and in the hyaline cap for some hours until the beginning of metamorphosis, whereas the fluorescence of the tip of the tail disappears. Following application of the antibody to Phallusia mamillata, the peripheral cells of the papillae of the newly hatched larvae were fluorescent and a bright fluorescence was also present between the two layers of the tunic above the papillae and the anterior part of the cephalenteron. We never observed fluorescence in the cells of the epidermis of the tail. Retinoic acid (RA) treatment has been used to confirm the localization on the papillae of the cells secreting the hatching enzyme. The larvae of Ciona intestinalis were able to hatch because the cells of the tip of the tail positively reacted to immunofluorescence stain with anti-hatching enzyme antibody. On the contrary Phallusia tnamillata larvae failed to hatch and did not show anti-hatching enzyme reaction in the tail.

Efeito da idade de lagartas de Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) no desempenho do parasitóide Campoletis flavicincta (Ashmead) (Hymenoptera: Ichneumonidae) e consumo foliar por lagartas parasitadas e não-parasitadas

Verificou-se o potencial de parasitismo de Campoletis flavicincta (Ashmead) (Hymenoptera: Ichneumonidae) sobre lagartas de Spodoptera frugiperda (Smith) de diferentes idades e o consumo foliar de lagartas parasitadas, em relação a não parasitadas. Quando foram oferecidas ao parasitóide lagartas de 3-d o número médio de lagartas parasitadas foi de 232/fêmea, número semelhante ao que foi obtido com lagartas de 2-d (182,0 lagartas/fêmea). Com lagartas de 4-5-d, o número médio de parasitismo foi, respectivamente, 80,7 e 71,0 indivíduos parasitados/fêmea. Lagartas sadias, durante todo o seu período de vida, consumiram, em média, 209,3 cm² de área foliar, enquanto que as lagartas parasitadas consumiram apenas 14,5 cm² (6,9% do consumo de uma lagarta sadia).

Activity of Bacillus thuringiensis Berliner Against Different Ages and Stages of Helicoverpa zea (Lepidoptera: Noctuidae) on Cotton

This study was done to compare the mortality of Helicoverpa zea (Boddie) eggs and larvae of different ages on cotton treated with Bacillus thuringiensis Berliner var. kurstaki. Mortality of H. zea neonates hatching from eggs collected from B. thuringiensis-treated cotton plots was significantly (P ≤ 0.01) higher for eggs 0 than 2 d in age at the highest (1.12kg/ha) rate, but did not differ at lower rates. However, across all rates the median lethal concentration (LC50) was 3.2-fold lower for larvae hatching from eggs that were 2 d in age than those from eggs 0 d in age. Mortality for larvae 1 d in age placed on B. thuringiensis-treated cotton terminals was significantly higher than for larvae 3 and 5 d in age at 4.48 and 8.96 kg/ha rates of B. thuringiensis. The LC50 for larvae 1 d in age (2.1 kg/ha) was 3 and 5.7-fold lower than for larvae 3 and 5 d in age, respectively (based on 95% confidence intervals). These data indicate that in cotton pest management systems, B. thuringiensis applications need to be directed at maximum oviposition and eclosion of H. zea neonates because control is very low against larger larvae.

Efficacy of injectable doramectin in the therapy and control of Dermatobia hominis infestations in Latin America

Three studies were conducted in Latin America, one in Brazil, one in Venezuela and one in Argentina, using a common protocol to investigate the efficacy of a single subcutaneous injection of doramectin at 200 μg kg −1 (1 ml per 50 kg) for the treatment and control of Dermatobia hominis infestations in cattle raised under commercial conditions. In each study, two groups of 20 animals each were allocated on the basis of D. hominis nodules present 24 h before treatment to a treated group (T1), or to a control group (T2) which received saline solution at 1 ml per 50 kg of live weight. All cattle were injected in the mid-dorsal cervical region and examined on treatment day and 2, 7, 15 and 30 days post-treatment (p.t.). At each observation day the number of D. hominis nodules was counted and the viability of the larvae inside them was assessed and recorded. Treatment with doramectin was 100% effective in eliminating D. hominis larvae and in controlling the re-establishment of the parasite under field conditions of continuous reinfestation. During the first 48 h p.t., dead larvae of different ages were found outside or partially outside the nodules in animals of the doramectin groups. After 48 h p.t., no live larvae were found inside existing nodules, nor did new nodules develop in animals of the doramectin groups in any of the three studies. When compared with nodule counts in the control group on the same observation day or with parasite burdens on the same animal before treatment, doramectin-treated animals began to eliminate parasitic nodules at 48 h p.t. Efficacy reached 100% at 7 days p.t. and remained at 100% on subsequent observation days ( P<0.05). None of the doramectin-treated animals exhibited any clinical signs of adverse reaction to medication.

Behavioral response of larval Atlantic menhaden Brevoortia tyrannus (Latrobe) and spot Leiostomus xanthurus (Lacépède) to rates of salinity change

Larval Atlantic menhaden [ Brevoortia tyrannus (Latrobe)] and spot [ Leiostomus xanthurus) (Lacépède)] are transported from the western Gulf Stream edge to bays and estuaries of the southeastern United States. Direction of water flow on the continental shelf varies with depth, allowing the potential for enhancement of shoreward transport by behavioral depth regulation, possibly in response to vertical salinity gradients. Salinity profiles from the North and South Carolina continental shelf were analyzed to quantify the salinity gradients in the field. Behavioral response to salinity was investigated by exposing laboratory spawned and reared menhaden and spot larvae of different ages to rates of salinity change in an experimental apparatus in the laboratory. At each rate of salinity change tested, five replicate runs were recorded each with groups of 30 to 50 larvae. Both species and age groups showed a significant ascent response upon salinity increases. Rates of increase of 0.28 and 0.13 × 10 −1 ppt · min −1 with absolute salinity increases of 0.8 and 0.3 ppt were thresholds for response by young (4–13 days post-hatching) and old (2–4 wk post hatching) menhaden larvae, respectively. For spot, rates of increase of 1.15 and 0.85 × 10 −1 ppt · min −1 with absolute salinity increases of 1.4 and 2.0 ppt were thresholds for response by young and old larvae, respectively. Response to decreasing salinity was absent in both species, thus decreasing salinity with depth would not cause larvae to descend. In nature, salinity gradients of sufficient magnitude for depth regulation, and possibly facilitating cross-shelf transport appear common for menhaden, but not for spot.

Ovipositional preferences and larval cannibalism in the Neotropical mosquito Trichoprosopon digitatum (Diptera: Culicidae)

Abstract. The effects of age, size, food availability and relatedness on larval cannibalism in the Neotropical mosquito Trichoprosopon digitatum were investigated. The eggs of this mosquito are laid in small water receptacles and guarded by females until they hatch. No significant differences in the median level of cannibalism were detected between larvae of the same age derived from the same and from different clutches. Only 4-day-old larvae showed a significantly higher median level of cannibalism at low than at high food levels. When larvae of different ages were placed together, cannibalism was highly size-dependent. A parallel series of experiments was conducted in the field to determine the ovipositional preferences of T. digitatum for pots that contained particular developmental stages of the mosquito. Adult females preferentially laid their eggs in (1) pots that contained high levels of food and (2) pots that already contained an adult female guarding its clutch. Adult females avoided laying into pots that contained 8-day-old larvae. The data suggest that the oviposition decisions of the mosquito reduce the chances of its offspring being consumed by conspecifics. It is unclear precisely why ovipositing females should prefer to lay where there are other recently laid eggs although there appears to be little fitness cost in terms of cannibalism.

Evaluation of a rapid mass-screening technique for measuring antibiosis to Helicoverpa spp. in cotton cultivars

A study of a variety of screening techniques was undertaken to determine their suitability for an antibiosis-enhancing cotton-breeding program. Techniques trialled included 9 different larval bioassays of varying durations on squares, leaves, and seedlings of cotton-using larvae of different ages. Chemical analyses of squares and seedlings, and a field trial to validate laboratory findings, were also conducted. The 'standard' measure of antibiosis in cotton plants, using long-term (8-day) bioassays based on larval weight gain, was found to be unsuitable for mass screening cotton plants for antibiosis to the cotton bollworm, Helicoverpa armigera (Hnbner), in Central Queensland. A 48-h technique using instar VI larvae proved as dependable as the standard, but faster and more energy-efficient, making it more suitable for mass screening. Chemical analyses supported previous findings that terpenoid aldehydes (i.e. gossypol) in cotton produce important antibiotic activity against H. armigera. Highly significant negative correlations were shown between gossypol content of ingested plant material and larval weight gains. In contrast, there was no relationship between condensed tannin content and larval weight gain. The relationships between larval bioassays and allelochemical content of cultivars were confirmed in a field trial.

Feeding behaviour in larvae of the opisthobranchPhiline aperta

In a study conducted in 1989 to 1990Philine aperta L. larvae of different ages were fed algal particles within the size range of 1.3 to 18 µm equivalent spherical diameter in incubation experiments in order to determine the ranges of particle sizes captured by larvae. The particle size spectrum ranged from 1.3 µm to ca. 7 µm for newly hatched veligers. The upper limit for ingestible particle size increased with larval age to 18 µm for late stage veligers just before metamorphosis. The development in food size range is explained by changes in morphological dimensions of velar structures. The food size spectrum forP. aperta is compared with spectra for other opposedciliar-band feeders. Results from particle selection experiments with three differently sized algae combined with direct observations of grazing individuals suggest that differential ingestion of different algal species is not a matter of behavioural grazing, but only a question of size.

Oculomotor (N III) motoneurons can innervate the superior oblique muscle of Xenopus after larval trochlear (N IV) nerve surgery

The position of motoneurons which reinnervate the superior oblique muscle (SOM), normally exclusively innervated by contralateral trochlear motoneurons, was studied in Xenopus using retrograde tracing techniques. The trochlear nerve was cut at its decussation in 49 larvae of different ages and, after subsequent regeneration, the total number of trochlear motoneurons was found to be reduced to about 50% of the controls. In contrast, the number of ipsilateral trochlear motoneurons was increased. Cutting the trochlear nerve at later stages may result in absence of this nerve. In some animals the SOM was innervated either by superior rectus or, more frequently, by inferior oblique motoneurons alone; the latter is known to act predominantly as an antagonist of the SOM.

Leaving home: predation and the dispersal of larvae from the maternal burrow of Bledius spectabilis, a subsocial intertidal beetle

Females of the intertidal subsocial beetle, Bledius spectabilis Kraatz (Staphylinidae), look after their eggs and young larvae in burrows in saltmarsh mud. Field observations showed that the beetle larvae disperse from the maternal burrow wowards the end of the first instar. The dispersing larvae belonged to a restricted age-group and dispersed only once, at night (between 2200 and 0400 hours). They moved rapidly on the surface of the saltmarsh soil in search of cracks and holes in which to start their own independent burrows. The nocturnal dispersal of the Bledius larvae overlapped with the activity on the soil surface of the predatory carabid beetle Dicheirotrichus gustavi Crotch. The ability of larvae of different ages to survive attack by the carabid was tested in field experiments. Young larvae taken from the maternal burrow were always eaten by the first carabid that attacked them. Older larvae taken from the maternal burrow and the dispersing larvae survived on average at least one attack by the carabid. By delaying dispersal until the latter part of the first instar, the larvae can significantly increase their chance of countering an attack by this predator during this critical phase. The maternal burrow therefore provides not only protection against the tide but a safe place in which the larvae can grow large enough to repulse predator attack.

Modifications of the effect of bleomycin in the somatic mutation and recombination test in Drosophila melanogaster

Exposure to oxygen has been implicated as an important mechanism of mutations, cancer and aging. Most data supporting this notion have been obtained in vitro, but the elaborate defense systems against oxygen stress in aerobic organisms make it difficult to extrapolate in vitro data to in vivo conditions. In the present investigation the somatic mutation and recombination test (SMART) in Drosophila with the wing spot system (Graf et al., 1984) has been used as an in vivo system to study the effect of oxygen radicals generated by bleomycin (BLM). BLM causes a dose-related increase of wing spots and this effect drastically increases by increasing oxygen in the atmosphere to 70%. Data from treatment of larvae of different ages, as well as post-treatment with oxygen, indicate that BLM can persist, presumably intercalated in DNA, and subsequently be activated by oxygen to generate free radicals. By the use of inversion heterozygosity, which eliminates somatic recombination, it was shown that the majority of wing spots induced by BLM emanate from somatic recombination. A small number of flies deviated from the rest by an abnormally high frequency of BLM-induced wing spots. Preliminary results from a selection of such flies indicate that this extreme resopnse to BLM is genetically determined. Treatment with BLM was also combined with agents known to interfere with the defense mechanisms against radicals or function as radical scavengers. Only ascorbic acid cotreatment had a modifying effect on BLM mutagenicity. The other agents did not alter or at most had a marginal effect on BLM mutagenicity. These data indicate that the defense mechanism do not constitute a limiting factor in this case. BLM intercalates between DNA bases, presumably giving little time and opportunity for modifying agents to react with radicals generated in direct contact with the gene targets. No effect of BLM was observed on male germ cells by measuring loss and non-disjunction of ring-X/Y, neither in air nor in a 70% oxygen atmosphere.