Analysis of X-ray irradiation effects on the mortality values and hemolymph immune cell composition of Apis mellifera and its parasite, Varroa destructor

Varroa destructor is one of the most destructive enemies of the honey bee, Apis mellifera all around the world. Several control methods are known to control V. destructor, but the efficacy of several alternative control methods remains unexplored. Irradiation can be one of these unknown solutions but before practical application, the effectiveness, and the physiological effects of ionizing radiation on the host and the parasite are waiting to be tested. Therefore, the objective of our study was to investigate the effects of different doses (15, 50, 100, and 150 Gy) of high-energy X-ray irradiation through mortality rates and hemocyte composition changes in A. mellifera workers and record the mortality rates of the parasite. The mortality rate was recorded during short-term (12, 24, and 48 h) and long-term periods (3, 6, 12, 18, and 24d). The sensitivity of the host and the parasite in case of the higher doses of radiation tested (50, 100, and 150 Gy) been demonstrated by total mortality of the host and 90 % of its parasite has been observed on the 18th day after the irradiation. V. destructor showed higher sensitivity (1.52-times higher than the adult honey bee workers) at the lowest dose (15 Gy). A. mellifera hemocytes were influenced significantly by radiation dosage and the elapsed time after treatment. The higher radiation doses increased plasmatocyte numbers in parallel with the decrease in prohemocyte numbers. On the contrary, the numbers of granulocytes and oencoytes increased in the treated samples, but the putative effects of the different dosages on the recorded number of these hemocyte types could not be statistically proven. In summary, based on the outcome of our study X-ray irradiation can be deemed an effective tool for controlling phoretic V. destructor. However, further research is needed to understand the physiological response of the affected organisms.

Does light influence the relationship between a native stem hemiparasite and a native or introduced host?

BACKGROUND AND AIMS

There have been very few studies investigating the influence of light on the effects of hemiparasitic plants on their hosts, despite the fact that hemiparasites are capable of photosynthesis but also access carbon (C) from their host. In this study we manipulated light availability to limit photosynthesis in an established hemiparasite and its hosts, and determined whether this affected the parasite's impact on growth and performance of two different hosts. We expected that limiting light and reducing autotrophic C gain in the parasite (and possibly increasing its heterotrophic C gain) would lead to an increased impact on host growth and/or host photosynthesis in plants grown in low (LL) relative to high light (HL).

METHODS

The Australian native host Leptospermum myrsinoides and the introduced host Ulex europaeus were either infected or not infected with the native stem hemiparasite Cassytha pubescens and grown in either HL or LL. Photosynthetic performance, nitrogen status and growth of hosts and parasite were quantified. Host water potentials were also measured.

KEY RESULTS

In situ midday electron transport rates (ETRs) of C. pubescens on both hosts were significantly lower in LL compared with HL, enabling us to investigate the impact of the reduced level of parasite autotrophy on growth of hosts. Despite the lower levels of photosynthesis in the parasite, the relative impact of infection on host biomass was the same in both LL and HL. In fact, biomass of L. myrsinoides was unaffected by infection in either HL or LL, while biomass of U. europaeus was negatively affected by infection in both treatments. This suggests that although photosynthesis of the parasite was lower in LL, there was no additional impact on host biomass in LL. In addition, light did not affect the amount of parasite biomass supported per unit host biomass in either host, although this parameter was slightly lower in LL than HL for U. europaeus (P = 0·073). We also found no significant enhancement of host photosynthesis in response to infection in either host, regardless of light treatment.

CONCLUSIONS

Despite lower photosynthetic rates in LL, C. pubescens did not increase its dependency on host C to the point where it affected host growth or photosynthesis. The impact of C. pubescens on host growth would be similar in areas of high and low light availability in the field, but the introduced host is more negatively affected by infection.

Getting ready for host invasion: elevated expression and action of xyloglucan endotransglucosylases/hydrolases in developing haustoria of the holoparasitic angiosperm Cuscuta

Changes in cell walls have been previously observed in the mature infection organ, or haustorium, of the parasitic angiosperm Cuscuta, but are not equally well charted in young haustoria. In this study, we focused on the molecular processes in the early stages of developing haustoria; that is, before the parasite engages in a physiological contact with its host. We describe first the identification of differentially expressed genes in young haustoria whose development was induced by far-red light and tactile stimuli in the absence of a host plant by suppression subtractive hybridization. To improve sequence information and to aid in the identification of the obtained candidates, reference transcriptomes derived from two species of Cuscuta, C. gronovii and C. reflexa, were generated. Subsequent quantitative gene expression analysis with different tissues of C. reflexa revealed that among the genes that were up-regulated in young haustoria, two xyloglucan endotransglucosylase/hydrolase (XTH) genes were highly expressed almost exclusively at the onset of haustorium development. The same expression pattern was also found for the closest XTH homologues from C. gronovii. In situ assays for XTH-specific action suggested that xyloglucan endotransglucosylation was most pronounced in the cell walls of the swelling area of the haustorium facing the host plant, but was also detectable in later stages of haustoriogenesis. We propose that xyloglucan remodelling by Cuscuta XTHs prepares the parasite for host infection and possibly aids the invasive growth of the haustorium.

Effects of Lobesia botrana (Lepidoptera: Tortricidae) egg age, density, and UV treatment on parasitism and development of Trichogramma cacoeciae (Hymenoptera: Trichogrammatidae)

Integrated pest management (IPM) supports the integration of all rational control methods available. Biological control is one of those control methods. Thus, the influence of Lobesia botrana Den. and Schiff. egg age, density, and sterilization by UV light on parasitism and progeny development of a Trichogramma cacoeciae Marchal strain from La Rioja, Spain, was studied. Understanding this influence is important for the development of biological control programs. UV-killed eggs are widely used for mass rearing Trichogramma. Trichogramma cacoeciae preferred young eggs (0-72 h old), and the largest number of progeny were produced from these eggs, especially from 48- to 72-h-old eggs. The relationship between the number of eggs parasitized by T. cacoeciae and its density (within the range studied) was linear (R (2) adjusted = 0.93), with constant values (72.2-93.7%) for discovery rate (an estimator of searching capacity). UV treatment did not affect the number of progeny produced or parasitism tendency and was thus a helpful tool for the mass-rearing process. Based on its response to egg age and density, our T. cacoeciae strain showed potential for control of L. botrana.

Modelling of effects due to chronic exposure of a fish population to ionizing radiation

A dynamic model was developed for description of radiation effects in an isolated fish population chronically exposed at different dose rates. The induced effects were predicted based on damage created by the radiation, recovery by means of repair mechanisms, and natural growth of the population. Three types of radiation effects (umbrella endpoints) were simulated--decrease of population size, decrease of reproductive capacity, and effects on the morbidity of the population. The influence of ecological interactions on the irradiated fish population was simulated using the combined action of radiation and parasite infestation as an example (ecological interaction "host-parasite"). The model calculations demonstrate that influence of ecological interactions can considerably aggravate the effects of radiation to an exposed population. It was concluded that development of standards for wildlife protection against ionizing radiation requires consideration of possible ecological interactions and to take into account the ecological effects of radiation.

Tri-trophic consequences of UV-B exposure: plants, herbivores and parasitoids

In this paper we demonstrate a UV-B-mediated link between host plants, herbivores and their parasitoids, using a model system consisting of a host plant Brassica oleracea, a herbivore Plutella xylostella and its parasitoid Cotesia plutellae. Ultraviolet-B radiation (UV-B) is a potent elicitor of a variety of changes in the chemistry, morphology and physiology of plants and animals. Recent studies have demonstrated that common signals, such as jasmonic acid (JA), play important roles in the mechanisms by which plants respond to UV-B and to damage by herbivores. Plant responses elicited by UV-B radiation can affect the choices of ovipositing female insects and the fitness of their offspring. This leads to the prediction that, in plants, the changes induced as a consequence of UV damage will be similar to those elicited in response to insect damage, including knock-on effects upon the next trophic level, predators. In our trials female P. xylostella oviposited preferentially on host plants grown in depleted UV-B conditions, while their larvae preferred to feed on tissues from UV-depleted regimes over those from UV-supplemented ones. Larval feeding patterns on UV-supplemented tissues met the predictions of models which propose that induced defences in plants should disperse herbivory; feeding scars were significantly smaller and more numerous--though not significantly so--than those on host plant leaves grown in UV-depleted conditions. Most importantly, female parasitoids also showed a clear pattern of preference when given the choice between host plants and attendant larvae from the different UV regimes; however, in the case of the female parasitoids, the choice was in favour of potential hosts foraging on UV-supplemented tissues. This study demonstrates the potential for UV-B to elicit a variety of interactions between trophic levels, most likely mediated through effects upon host plant chemistry.

Orientation response of haematophagous bugs to CO2: the effect of the temporal structure of the stimulus

Carbon dioxide is generally recognized as an important cue used by haematophagous insects to locate a food source. When the mammalian hosts of these insects breathe, they normally emanate considerable amounts of CO2 at discrete intervals, i.e. with each exhalation. In this work, we analysed the effect of temporally pulsing CO2 on the host-seeking behaviour of Triatoma infestans. We investigated the ability of T. infestans to follow continuous and intermittent air pulses of 0.25, 0.5 and 1 Hz that included different concentrations of CO2. We found that insects were attracted to pulsed airstreams of 0.25 and 0.5 Hz transporting 400 ppm of CO2 above the ambient levels and to continuous streams added with the same amount of CO2. On the other hand, insects walked away from streams pulsed at rates of 1 Hz regardless of the amount of CO2 they bear. The walking trajectories displayed by bugs to attractive CO2-pulsed streams were as rectilinear and accurate as those to CO2-continuous streams. Our results are discussed in the frame of the interaction between olfactory and mechanoreceptive inputs as affecting the behavioural response of bugs.

Effects of gamma radiation on Brugia malayi infective larvae and their intracellular Wolbachia bacteria

Prior studies have shown that irradiated filarial larvae are developmentally stunted but capable of inducing partial immunity to filariasis in animals. The mechanisms for these effects are poorly understood. Recent studies suggest that intracellular Wolbachia bacteria are necessary for the normal development, reproduction and survival of filarial nematodes. The purpose of this study was to examine the effects of irradiation on Wolbachia in Brugia malayi infective larvae (L3) and on L3 development. The L3 were exposed to 0, 25, 35, 45, 55, 65 or 75 krad of gamma irradiation from a (137) Cesium source and cultured in vitro at 37 degrees C in NCTC/IMDM medium with 10% FCS for 12 days. Irradiation prevented molting of L3 to the L4 stage in a dose-dependent manner. Electron microscopy studies showed that irradiation damaged Wolbachia (25 krad) or cleared them from worm tissues (45 krad). In addition, majority of the irradiated L3s failed to develop the L4 cuticle. Real-time PCR studies showed that irradiation reduced Wolbachia DNA in worm tissues. Parallel in vivo studies confirmed decreased development of irradiated L3 in jirds, with associated effects on Wolbachia. Jirds injected s.c with normal L3 developed antibodies to Wolbachia surface protein (wsp) shortly after the onset of microfilarial patency. In contrast, jirds injected with irradiated L3 did not develop microfilaremia or antibodies to wsp. Additional studies are needed to test the hypothesis that irradiation retards growth and development of filarial L3 by killing Wolbachia.

UV radiation effects on pathogens and insect pests of greenhouse-grown crops

Production of high-value crops is often performed under protected cultivation. In recent years various spectral modifications have been made in greenhouse covers. Two of the main reasons to modify the spectral characteristics of greenhouse covers have been to suppress the proliferation of several foliar diseases and to protect crops from insects and insect-borne virus diseases of greenhouse-grown crops. These goals were achieved by complete or partial absorption of solar UV radiation, which interrupts the life cycle of several fungal pathogens and alters the visual behavior of many insects. Examples of these management strategies are described in this article.

Circadian rhythm of behavioural responsiveness to carbon dioxide in the blood-sucking bug Triatoma infestans (Heteroptera: Reduviidae)

The temporal modulation of the behavioural response to carbon dioxide and its chronobiological basis were investigated in larvae of Triatoma infestans. We analysed the orientation towards CO(2) of insects kept under three different illumination regimes: (1) 12 h light/12 h darkness cycles (L/D), (2) constant darkness (D/D) and (3) constant light (L/L). When maintained under L/D conditions, insects exhibited an oriented response towards airstreams added with 1500 ppm of CO(2) during the first hours of the scotophase only. Bugs maintained under D/D also showed a positive orientation response towards CO(2) during the first hours of the subjective night, while bugs kept under L/L did not show a rhythmic oriented behaviour. Thus, T. infestans displayed a daily rhythm of orientation towards CO(2) (i.e. a potential food source) only at the beginning of the scotophase. The persistence of the rhythm under constant darkness reveals the existence of an endogenous circadian control of this behaviour.

Dispersal and parasitizing abilities of Eupelmus vuilleti (Hymenoptera: Eupelmidae) within a column of cowpea seeds

Eupelmus vuilleti (Crawford) is an ectoparasitoid of the seed-eating beetle Bruchidius atrolineatus (Pic), which is an important pest of stored cowpea, Vigna unguiculata Walp, seeds in West Africa. Herein, we investigated the dispersal abilities of females within columns of seeds to assess the potential of E. vuilleti as a biological control agent of bruchids in cowpea granaries. The influence of host presence together with the 2 abiotic factors light and gravity on parasitoid movement and parasitization efficiency were analyzed. E. vuilleti females were able to travel through large seed masses and parasitize hosts located at the end of the seed column opposed to their introduction zone. Parasitoid movement was stimulated by light. E. vuilleti females exhibited a negative geotropism. Females introduced at the bottom of the seed column dispersed more and parasitized more hosts than females introduced at the top. Host presence had some influence on the dispersal of the parasitoids within the seed column at a host density of 10 infested seeds for 16,000-18,000 uninfested seeds. This depended on female introduction zone because gravity was the major factor influencing dispersal. The possible applications of these results for biological control of bruchids in cowpea granaries are discussed.

[The host-opportunistic protozoa system. The incidence of mixed infections (Pneumocystis and cytomegalovirus) in children living in radionuclide-contaminated areas]

The purpose of our study was to determine the influence of ionized radiation onto the frequency of mixed infections (P. carinii and Cytomegalovirus) in children inhabitants of the settlements affected with radionuclide after Chernobyl accident. Two groups of children were under survey. 1) 103 inhabitants of Novozybkov (Bryansk Province, Russia) and 38 patients under observation in Moscow paediatric hospital from another affected villages (5-15 Ci/km2) were examined serologically by the diagnostic system "Pneumo-test" and "Cytomegatest" (Nyarmedic, Moscow, Russia). Cut-off titers for P. carinii were IgM-1: 200, IgG-1: 20, for CMV IgG-1: 200, 2) Retrospective study of 563 patients with respiratory pathology and 1809 died children after acute pneumonia during 14 years period. Sputum and mucus of the patients taken by laryngoscopy and bronchoscopy were studied for P. carinii by microscopy, the section of lungs--histologically. The sediments of urine and saliva were examined for CMV by microscopy and section of different organs_-histologically. Examinations were performed by one and the same highly qualified pathologist. The results of the study were as follows. 1. Of 563 children examined for both P. carinii and CMV 186 (33%) were positive for P. carinii and 189 (33.7%) for CMV. Both pathogens were found in 46 children (8.2%), mainly among 1-2 and 6-12 month age (8.5 and 14.5%, respectively). Retrospective analysis of 1809 autopsy results shows, that in 73 cases (4%) were found only P. carinii, in 200 (11.1%) only CMV and in 24 (1.3%) two pathogens simultaneously. 2. Of 103 children surveyed serologically P. carinii monoinfection was found in 7 (8.8%), CMV-in 25 (24.3%) and coinfection in 55 (53.4%). Estimated frequency for coinfection (if combination of two infections were to be accidental) should equal 46.8%. In control group consisted of 30 children from clean Moscow region the rate of coinfection was 16.7% and estimated rate 15% (the difference between empiric and estimated rates are statistically significant, t > 4). Thus it is clear that the rate of coinfection of P. carinii and CMV is always high either in clean or in affected by ionized radiation regions. This rate determined by microscopy was higher in patients (8.2%) than in autopsy cases (1.3%) and much higher in children from affected region (53.3%) than in control (16.7%), being determined serologically. Separate interest present geometric mean titers found in the cases of coinfection. The titer for anti-CMV IgG in children from affected regions was rather high (5884 vs. 1246 in control) and on the contrary titers for anti-P. carinii IgM and IgG were lower than in control (512 vs. 1245 and 58 vs. 159 respectively). We are incline to interpret the results of our study as evidence of increased susceptibility to P. carinii and CMV in those children whose immune system was suppressed by premorbid factors or ionized radiation and peculiar symbiotic relationships of P. carinii and CMV resulting in enhancement of their infectiousness.

[The host-opportunistic protozoa system. The effect of ionizing radiation on the prevalence of cryptosporidiosis and pneumocystosis]

The aim of this study was to determine an influence of ionized radiation on the prevalence of Cryptosporidium and Pneumocystis carinii (P. c.) infections in children inhabitants of settlements affected by radionuclides after Chernobyl accident. Survey of children from day-care centers for prevalence of Cryptosporidium was carried out in Bryansk region, Russia, and Gomel and Mogilev regions, Belarus; children from cities Mogilev and Gomel as well as small town Pochep, Bryansk region, serve as control clean zones. Survey for P. c. seroprevalence was carried out in town Novozybkov, Bryansk region, Specific Ab to P. c. determined by "Pneumo-test" system (Nyarmedic. Moscow. Russia), an evaluation of immune status included assessment of Ig in serum and saliva by Manchini method. Results of the study were as follows: 1) of 432 healthy children surveyed for Cryptosporidium oocysts 352 were from affected regions: the prevalence in Bryansk region was 8% vs. 2.8% in control, in Gomel and Mogilev 4.1% vs. 2.8%. 2) Prevalence anti-P.c. Ab accounts 56.3% in children and 78.2% in adult inhabitants of Novozybkov vs. 30% in children of control group. Special interest presents an relationship of seroprevalence P.c. and secretory immunity examined twice with 2 month interval. At the first survey IgG in seropositive for P. c. children was found in 36.8% (vs. 23.1% in control) and secretary IgA in 13.2% vs. 5.8% in control. At the second survey IgG was found in 53.4% vs. 21.8% and IgA in 2.7% vs. 1.8% in control. Taking into consideration the known fact that IgG and IgA in saliva are result of their transudation from blood through the inflammatory mucosa we consider that long ionized radiation impairs the barrier function of mucosae.