[show abstract][hide abstract] ABSTRACT: Large-scale losses of honey bee colonies represent a poorly understood problem of global importance. Both biotic and abiotic factors are involved in this phenomenon that is often associated with high loads of parasites and pathogens. A stronger impact of pathogens in honey bees exposed to neonicotinoid insecticides has been reported, but the causal link between insecticide exposure and the possible immune alteration of honey bees remains elusive. Here, we demonstrate that the neonicotinoid insecticide clothianidin negatively modulates NF-κB immune signaling in insects and adversely affects honey bee antiviral defenses controlled by this transcription factor. We have identified in insects a negative modulator of NF-κB activation, which is a leucine-rich repeat protein. Exposure to clothianidin, by enhancing the transcription of the gene encoding this inhibitor, reduces immune defenses and promotes the replication of the deformed wing virus in honey bees bearing covert infections. This honey bee immunosuppression is similarly induced by a different neonicotinoid, imidacloprid, but not by the organophosphate chlorpyriphos, which does not affect NF-κB signaling. The occurrence at sublethal doses of this insecticide-induced viral proliferation suggests that the studied neonicotinoids might have a negative effect at the field level. Our experiments uncover a further level of regulation of the immune response in insects and set the stage for studies on neural modulation of immunity in animals. Furthermore, this study has implications for the conservation of bees, as it will contribute to the definition of more appropriate guidelines for testing chronic or sublethal effects of pesticides used in agriculture.
Proceedings of the National Academy of Sciences 10/2013; · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Tick-borne zoonoses are considered as emerging diseases. Tick repellents represent an effective tool for reducing the risk of tick bite and pathogens transmission. Previous work demonstrated the repellent activity of the phenylpropanoid eugenol against Ixodes ricinus; here we investigate the relationship between molecular structure and repellency in a group of substances related to that compound. We report the biological activity of 18 compounds varying for the presence/number of several moieties, including hydroxyl and methoxy groups and carbon side-chain. Each compound was tested at different doses with a bioassay designed to measure repellency against individual tick nymphs. Both vapor pressure and chemical features of the tested compounds appeared to be related to repellency. In particular, the hydroxyl and methoxy groups as well as the side-chain on the benzene ring seem to play a role. These results are discussed in light of available data on chemical perception in ticks. In the course of the study new repellent compounds were identified; the biological activity of some of them (at least as effective as the "gold standard" repellent DEET) appears to be very promising from a practical point of view.
PLoS ONE 01/2013; 8(6):e67832. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Very rapidly after Varroa destructor invaded apiaries of Apis mellifera, the devastating effect of this mite prompted an active research effort to understand and control this parasite. Over a few decades, varroa has spread to most countries exploiting A. mellifera. As a consequence, a large number of teams have worked with this organism, developing a diversity of research methods. Often different approaches have been followed to achieve the same goal. The diversity of methods made the results difficult to compare, thus hindering our understanding of this parasite. In this paper, we provide easy to use protocols for the collection, identification, diagnosis, rearing, breeding, marking and measurement of infestation rates and fertility of V. destructor. We also describe experimental protocols to study orientation and feeding of the mite, to infest colonies or cells and measure the mite’s susceptibility to acaricides. Where relevant, we describe which mite should be used for bioassays since their behaviour is influenced by their physiological state. We also give a method to determine the damage threshold above which varroa damages colonies. This tool is fundamental to be able to implement integrated control concepts. We have described pros and cons for all methods for the user to know which method to use under which circumstances. These methods could be embraced as standards by the community when designing and performing research on V. destructor.
Journal of Apicultural Research 11/2012; 52(1):1-54. · 1.93 Impact Factor
[show abstract][hide abstract] ABSTRACT: Several factors threaten the health of honeybees; among them the parasitic mite Varroa destructor and the Deformed Wing Virus play a major role. Recently, the dangerous interplay between the mite and the virus was studied in detail and the transition, triggered by mite feeding, from a benign covert infection to a devastating viral outbreak, characterized by an intense viral replication, associated with some characteristic symptoms, was described. In order to gain insight into the events preceding that crucial transition we carried out standardized lab experiments aiming at studying the effects of parasitization in asymptomatic bees to establish a relationship between such effects and bee mortality. It appears that parasitization alters the capacity of the honeybee to regulate water exchange; this, in turn, has severe effects on bee survival. These results are discussed in light of possible novel strategies aiming at mitigating the impact of the parasite on honeybee health.
Journal of insect physiology 10/2012; · 2.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: The health of the honeybee and, indirectly, global crop production are threatened by several biotic and abiotic factors, which play a poorly defined role in the induction of widespread colony losses. Recent descriptive studies suggest that colony losses are often related to the interaction between pathogens and other stress factors, including parasites. Through an integrated analysis of the population and molecular changes associated with the collapse of honeybee colonies infested by the parasitic mite Varroa destructor, we show that this parasite can de-stabilise the within-host dynamics of Deformed wing virus (DWV), transforming a cryptic and vertically transmitted virus into a rapidly replicating killer, which attains lethal levels late in the season. The de-stabilisation of DWV infection is associated with an immunosuppression syndrome, characterized by a strong down-regulation of the transcription factor NF-κB. The centrality of NF-κB in host responses to a range of environmental challenges suggests that this transcription factor can act as a common currency underlying colony collapse that may be triggered by different causes. Our results offer an integrated account for the multifactorial origin of honeybee losses and a new framework for assessing, and possibly mitigating, the impact of environmental challenges on honeybee health.
[show abstract][hide abstract] ABSTRACT: A 2-year study was conducted in a mountainous area of northeast Italy to evaluate the occurrence and distribution of ticks, as well as to assess the prevalence of the spirochaete Borrelia burgdorferi sensu lato. All ticks collected were Ixodes ricinus L. (Parasitiformes: Ixodidae). In general, most nymphs and adult ticks were collected from April to July. Tick density was highly variable among sites; however, two areas with different infestation levels were recognized. Prevalences of B. burgdorferi s.l. in nymphal stages were rather variable between sites; overall the prevalence of infected nymphs in the whole area was slightly higher than 20%. The prevalence of B. burgdorferi s.l. in nymphs does not seem to be correlated with nymph density. The correlation between the incidence of Lyme borreliosis (reported human cases/1000 inhabitants/year) and Borrelia prevalence in nymphs was not significant, although a significant correlation was found between borreliosis incidence and nymph density.
Medical and Veterinary Entomology 09/2010; 24(3):220-6. · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: The parasitic mite, Varroa destructor, is the most important threat for apiculture in most bee-keeping areas of the world. The mite is carried to the bee brood cell, where it reproduces, by a nurse bee; therefore the selection of the bee stage by the parasite could influence its reproductive success. This study investigates the role of the cuticular hydrocarbons of the European honeybee (Apis mellifera) in host-selection by the mite. Preliminary laboratory bioassays confirmed the preference of the varroa mite for nurse bees over pollen foragers. GC-MS analysis of nurse and pollen bees revealed differences in the cuticular hydrocarbons of the two stages; in particular, it appeared that pollen bees have more (Z)-8-heptadecene than nurse bees. Laboratory experiments showed that treatment of nurse bees with 100 ng of the pure compound makes them repellent to the varroa mite. These results suggest that the mite can exploit the differences in the cuticular composition of its host for a refined selection that allows it to reach a brood cell and start reproduction. The biological activity of the alkene encourages further investigations for the development of novel control techniques based on this compound.
[show abstract][hide abstract] ABSTRACT: In Alpine area of extreme North Eastern Italy the first autochthonous case of TBE was reported in 1998 and was followed by 45 cases during the period 2001-2007, thus defining this area as definitely endemic. An ecological survey evaluated the tick density and the Tick-borne encephalitis virus (TBEV) infection prevalence in tick collected in selected sites. In addition, TBE strains were characterized by sequencing and phylogenetic analysis. Overall, 2,361 ticks (2,198 nymphs and 163 adults) of the Ixodes ricinus L. species collected during 2005 and 2006 were examined. Five samples were positive for TBEV, corresponding to an overall prevalence rate of 0.21%. When analyzed by place, TBEV was discovered in three sites where the highest tick density was found. The difference of prevalence between high and low density areas tested to be statistically significant (P = 0.028). Phylogenetic analysis showed that four sequences clustered with the Neudoerfl prototype, while the other clustered with the Isosaari 17 strain and with a number of Slovenian isolates. In addition, a sequence detected in archival samples from one human case segregated with another variant, namely the Swedish Torö strain.
Journal of Medical Virology 03/2009; 81(2):309-16. · 2.37 Impact Factor
[show abstract][hide abstract] ABSTRACT: The mite Varroa destructor Anderson & Trueman is a parasite of the honeybee Apis mellifera L. and represents a major threat for apiculture in the Western world. Reproduction takes place only inside bee brood cells that are invaded just before sealing; drone cells are preferred over worker cells, whereas queen cells are not normally invaded. Lower incidence of mites in queen cells is at least partly due to the deterrent activity of royal jelly. In this study, the repellent properties of royal jelly were investigated using a lab bioassay. Chemical analysis showed that octanoic acid is a major volatile component of royal jelly; by contrast, the concentration is much lower in drone and worker larval food. Bioassays, carried out under lab conditions, demonstrated that octanoic acid is repellent to the mite. Field studies in bee colonies confirmed that the compound may interfere with the process of cell invasion by the mite.
[show abstract][hide abstract] ABSTRACT: Diseases transmitted by ticks are causing increasing concern in Europe and all around the world. Repellents are an effective measure for reducing the risk of tick bite; products based on natural compounds represent an interesting alternative to common synthetic repellents. In this study the repellency of sweet basil (Ocimum basilicum L.) was tested against the tick Ixodes ricinus L., by using a laboratory bioassay. A bioassay-assisted fractionation allowed the identification of a compound involved in the biological activity. Eugenol appeared to be as repellent as DEET at two tested doses. Linalool, which was identified in the active fraction too, failed to give any response. Repellency of eugenol was proved also in the presence of human skin odour using a convenient and practical bioassay.
Experimental and Applied Acarology 09/2008; 45(3-4):219-28. · 1.85 Impact Factor
[show abstract][hide abstract] ABSTRACT: A laboratory study on the chemical cues influencing the behaviour of Acanthoscelides obtectus (Coleoptera, Bruchidae) on dry bean seeds was carried out to identify possible semiochemicals affecting the oviposition of the beetle.In an olfactometer, A. obtectus females preferred the odour of clean beans to that of beans where conspecifics had developed; an ether extract of such beans was repellent to the insect. Some hydrocarbons that are repellent to females were identified; the effect of heptacosane on the oviposition was studied.
Journal of Stored Products Research - J STORED PROD RES. 01/2008; 44(2):108-114.
[show abstract][hide abstract] ABSTRACT: A mixed microbial culture degrading fumonisin B l was obtained from soil samples using an enrichment culture procedure. A bacterial isolate from the enrichment culture (strain NCB 1492) degraded fumonisin B1 after incubation for 3 h, as indicated by TLC and HPLC analysis. On the basis of the sequence analysis of 16S rDNA, strain NCB 1492 was related to the Delftia/Comamonas group. Thin-layer chromatographic analysis indicated the presence of metabolites in the NCB 1492 culture filtrates after degradation of fumonisin B1 supplied as sole carbon and nitrogen source in phosphate buffer. Four metabolites were identified by mass spectrometry analysis.
[show abstract][hide abstract] ABSTRACT: Male and female adult wasps belonging to the atomus group of the genus Anagrus Haliday, classified according to morphological techniques, were analyzed for their cuticular hydrocarbons to detect any possible differences between species. Most female specimens that were identified as either A. atomus L. or A. ustulatus Haliday, using morphological and morphometrical characters, showed two distinct cuticular hydrocarbon profiles. These profiles seemed to be independent of the plants the insects were collected from, the potential leafhopper host species (Hemiptera: Cicadellidae), and the emergence period, and they were largely consistent with classification based on morphology. Both A. atomus and A. ustulatus females were shown to emerge from leafhopper eggs found on Vitis vinifera L. (Vitaceae). Males, for which conclusive diagnostic characters are not yet available, showed the same two cuticular hydrocarbon patterns observed in females; on average, specimens displaying one hydrocarbon profile differed from those showing the other profile in three characters used for morphometrical analysis.
The Canadian Entomologist 01/2006; 138(3):348-356. · 0.90 Impact Factor
[show abstract][hide abstract] ABSTRACT: The alkene (Z)-8-heptadecene, a semiochemical which inhibits the reproduction of Varroa destructor was tested in natural comb cells. One-hundred ng of (Z)-8-heptadecene applied under the capping of worker cells, sealed 0–15 h previously, caused a highly significant reduction both in the number of offspring (–12% reduction) and in the number of potentially mated daughters per female (–28% reduction) in single infested cells. No reduction was observed in multiple infested cells. A consistent, but not significant decrease was observed in cells treated at different times after capping. No decrease in mite reproduction was noted in cells treated 0–16 h before capping or 0–6 h after capping. However, infestation of cells treated before capping was reduced by 41%. In single infested cells in the control groups, the number of potentially mated daughters per female decreased from 1.5 in June to 0.78–0.94 in September. The proportion of treated cells emptied by bees was about 30% lower than that of control cells. (Z)-8-Heptadecene may play an important role in the host-parasite relationship.
[show abstract][hide abstract] ABSTRACT: Hygienic behaviour of bees towards mite infested brood is involved in the tolerance of some bee strains to Varroa destructor. The stimuli triggering hygienic behaviour are olfactory cues emanating from cells containing infested brood but their identity is still unknown. After confirming the capacity of bees to detect and empty mite-infested cells, we studied the volatile chemicals released by artificially infested worker brood cells by means of SPME-GC-MS. The identified chemicals were then bioassayed by comparing the bees' hygienic behaviour towards treated cells into which 1 $\mu$g of each compound was injected and control cells which received the solvent alone. Z-(6)-pentadecene significantly increased the number of cells emptied by the bees.
[show abstract][hide abstract] ABSTRACT: Chemical stimuli responsible for the biological activity of bee larval food on Varroa destructor were studied both in the laboratory and under natural conditions. Loss of activity after neutralization and air entrainment experiments suggested that active substances were acidic and volatile. Linear, branched and aromatic carboxy-acids, as well as hydroxy-acids, were identified by GC-MS and SPME-GC-MS analysis in organic larval food extracts. The low molecular weight carboxy-acids identified were tested in a laboratory assay using a four-well arena. All the acids tested were inactive with the exception of 2-hydroxyhexanoic acid; comparison with related compounds and dose-response studies confirmed the activity of this acid at 10 and 100 ng per well showing that this is a semiochemical for the mite. One hundred nanograms of 2-hydroxyhexanoic acid applied to worker brood cells before capping increased by 36% the number of mites per cell in the treated brood compared to the control cells.
[show abstract][hide abstract] ABSTRACT: The parasitic mite Varroa destructor Anderson and Trueman, the most serious threat to apiculture in many countries of the world, reproduces inside honeybee brood cells. Previous research, using artificial cells for rearing the mite on an Apis mellifera larva, indicated that semiochemicals affecting the reproduction of Varroa destructor are released into such cells. In order to isolate these semiochemicals, infested artificial cells were extracted with hexane and the extract fractionated twice. Several unsaturated hydrocarbons were identified in the active fraction; some of them were released in higher amounts in case of infestation and were, therefore, bioassayed for their effect on the mite's reproduction. Of five alkenes tested under laboratory conditions, (Z)-8-heptadecene, caused a 30% reduction in the mean number of offspring of mites reared in cells treated with this compound.
Journal of Chemical Ecology 12/2002; 28(11):2181-90. · 2.46 Impact Factor