Search

Within any one habitat, the relative fitness of organisms in a population can vary substantially. Social insects like the common wasp are among the most successful invasive animals, but show enormous variation in nest size and other fitness-related traits. Some of this variation may be caused by pathogens such as viruses that can have serious consequences in social insects, which range from reduced productivity to colony death. Both individual immune responses and colony-level traits such as genetic diversity are likely to influence effects of pathogen infections on colony fitness. Here we investigate how infections with Kashmir Bee Virus (KBV), immune response and intracolony genetic diversity (due to queen polyandry) affect nest size in the invasive common wasp Vespula vulgaris. We show that KBV is highly prevalent in wasps and expression of antiviral immune genes is significantly increased with higher viral loads across individuals. Patriline membership within a nest did not influence KBV susceptibility or immune response. A permutational MANCOVA revealed that polyandry, viral load and expression of the immune gene Dicer were significant predictors of variation in nest size. High intracolony genetic diversity due to polyandry has previously been hypothesized to improve colony-level resistance to parasites and pathogens. Consistent with this hypothesis, we observed genetically diverse colonies to be significantly larger and to produce more queens, although this effect was not driven by the pathogen we investigated. Invasive wasps clearly suffer from pathogens and expend resources, as indicated here by elevated immune gene expression, toward reducing pathogen-impact on colony fitness. [ABSTRACT FROM AUTHOR]

Viruses are one of the major threats for honeybees and until now more than 20 different viruses have been discovered. Viruses and their hosts are engaged in a continuous arms race in which viral defense mechanisms drive the adaptive evolution of host immune genes, which in turn results in counter-adaptations of the viral immune antagonists. The honeybee immune responses to non-viral pathogens have been extensively studied, but little is known about the antiviral responses. Recent evidence suggests that the main mechanism of antiviral defense in insects is the RNA interference (RNAi) pathway. Furthermore, there is evidence that some viruses suppress this RNAi pathway in order to evade antiviral immunity. In the present study, we test this hypothesis by comparing the gene expression levels of some key components of the RNAi response of honeybees that were naturally infected with at least five viruses with those who were infected with only two or three viruses using a colorimetric microarray developed in-house, called BeeClinic, and subsequently confirmed by quantitative reverse-transcription-polymerase chain reaction (qRT-PCR). Our results show that key components of the RNAi pathway are indeed downregulated in highly infected bees. We were able to show that high virus loads suppress key RNAi components, which results in a counteraction of the host RNAi antiviral defense. As the RNAi is a primary defense against viruses, these findings shed new light on pathogen-host interactions and can help mitigate escalating colony losses worldwide. [ABSTRACT FROM AUTHOR]

The potential for infectious pathogens to spillover and emerge from managed populations to wildlife communities is poorly understood, but ecological, evolutionary and anthropogenic factors are all likely to influence the initial exposure and subsequent infection, spread and impact of disease. Fast-evolving RNA viruses, known to cause severe colony losses in managed honeybee populations, deserve particular attention for their propensity to jump between host species and thus threaten ecologically and economically important wild pollinator communities., We review the literature on pollinator viruses to identify biological and anthropogenic drivers of disease emergence, highlight gaps in the literature, and discuss potential management strategies., We provide evidence that many wild pollinator species are exposed to viruses from commercial species, resulting in multiple spillover events. However, it is not clear whether species become infected as a result of spillover or whether transmission is occurring within these wild populations. Ecological traits of pollinating insects, such as overlapping ranges, niches and behaviours, clearly promote cross-species transmission of RNA viruses. Moreover, we conclude that the social behaviour and phylogenetic relatedness of social pollinators further facilitate within- and between-host transmission, leaving these species particularly vulnerable to emerging diseases., We argue that the commercial use of pollinators is a key driver of disease emergence in these beneficial insects and that this must be addressed by management and policy., Synthesis and applications. There are important knowledge gaps, ranging from disease distribution and prevalence, to pathogen life history and virulence, to the impacts of disease emergence, which need to be addressed as research priorities. It is clear that avoiding anthropogenic pathogen spillover is crucial to preventing and managing disease emergence in pollinators, with far-reaching effects on our food security, ecosystem services and biodiversity. We argue that it is crucial to prevent the introduction of diseased pollinators into natural environments, which can be achieved through improved monitoring and management practices. [ABSTRACT FROM AUTHOR]

Many parasites alter host behaviour to enhance their chance of transmission. Recently, the ecdysteroid UDP-glucosyl transferase ( egt) gene from the baculovirus Lymantria dispar multiple nucleopolyhedrovirus (Ld MNPV) was identified to induce tree-top disease in L. dispar larvae. Infected gypsy moth larvae died at elevated positions (hence the term tree-top disease), which is thought to promote dissemination of the virus to lower foliage. It is, however, unknown whether egt has a conserved role among baculoviruses in inducing tree-top disease. Here, we studied tree-top disease induced by the baculovirus Autographa californica multiple nucleopolyhedrovirus (Ac MNPV) in two different host insects, Trichoplusia ni and Spodoptera exigua, and we investigated the role of the viral egt gene therein. Ac MNPV induced tree-top disease in both T. ni and S. exigua larvae, although in S. exigua a moulting-dependent effect was seen. Those S. exigua larvae undergoing a larval moult during the infection process died at elevated positions, while larvae that did not moult after infection died at low positions. For both T. ni and S. exigua, infection with a mutant Ac MNPV lacking egt did not change the position where the larvae died. We conclude that egt has no highly conserved role in inducing tree-top disease in lepidopteran larvae. The conclusion that egt is a 'gene for an extended phenotype' is therefore not generally applicable for all baculovirus-host interactions. We hypothesize that in some baculovirus-host systems (including Ld MNPV in L. dispar), an effect of egt on tree-top disease can be observed through indirect effects of egt on moulting-related climbing behaviour. [ABSTRACT FROM AUTHOR]

Some animals change their feeding behaviour when infected with parasites, seeking out substances that enhance their ability to overcome infection. This 'self-medication' is typically considered to involve the consumption of toxins, minerals or secondary compounds. However, recent studies have shown that macronutrients can influence the immune response and that pathogen-challenged individuals can self-medicate by choosing a diet rich in protein and low in carbohydrates. Infected individuals might also reduce food intake when infected (i.e. illness-induced anorexia)., Here, we examine macronutrient self-medication and illness-induced anorexia in caterpillars of the African armyworm ( Spodoptera exempta) by asking how individuals change their feeding decisions over the time course of infection with a baculovirus. We measured self-medication behaviour across several full-sib families to evaluate the plasticity of diet choice and underlying genetic variation., Larvae restricted to diets high in protein ( P) and low in carbohydrate ( C) were more likely to survive a virus challenge than those restricted to diets with a low P : C ratio. When allowed free choice, virus-challenged individuals chose a higher protein diet than controls., Individuals challenged with either a lethal or sublethal dose of virus increased the P : C ratio of their chosen diets. This was mostly due to a sharp decline in carbohydrate intake, rather than an increased intake of protein, reducing overall food intake, consistent with an illness-induced anorexic response. Over time the P : C ratio of the diet decreased until it matched that of controls., Our study provides the clearest evidence yet for dietary self-medication using macronutrients and shows that the temporal dynamics of feeding behaviour depends on the severity and stage of the infection. The strikingly similar behaviour shown by different families suggests that self-medication is phenotypically plastic and not a consequence of genetically based differences in diet choice between families. [ABSTRACT FROM AUTHOR]

Deformed wing virus (DWV) is a serious pathogen of the honey bee, Apis mellifera L., vectored by the parasitic mite Varroa destructor. The virus is associated with wing deformity in symptomatic bees, and premature death and reduced colony performance in asymptomatic bees. In the present study we reduced DWV infection by feeding both first instar larvae and adult A. mellifera with a double-stranded (ds) RNA construct, DWV-dsRNA, which is specific to DWV in DWV-inoculated bees, by mixing it with their food. We showed that feeding DWV to larvae causes wing deformity in adult bees in the absence of varroa mites and decreases survival rates of adult bees relative to bees not fed DWV. Feeding larvae with DWV-dsRNA in advance of inoculation with virus reduced the DWV viral level and reduced wing deformity relative to larvae fed DWV or DWV with green fluorescent protein-dsRNA (probably a result of RNA silencing), but did not affect survival to the adult stage. Feeding DWV-dsRNA did not affect larval survival rates, which suggests that dsRNA is non-toxic to larvae. Feeding adult workers with DWV-dsRNA in advance of inoculation with virus increased their longevity and reduced DWV concentration relative to controls. [ABSTRACT FROM AUTHOR]

Sublethal viral infections can cause changes in the body size and demography of insect vectors, with important consequences for population dynamics and the probability that individual mosquitoes will transmit disease. This study examined the effects of covert (sublethal) infection by Invertebrate iridescent virus 6 (IIV-6) on the demography of female Aedes aegypti and the relationship between key life history parameters in covertly infected female insects compared with healthy (control) insects or non-infected mosquitoes that had survived exposure to virus inoculum without becoming infected. Of the female mosquitoes that emerged following exposure to virus inoculum and were offered blood meals, 29% (43/150) proved positive for covert IIV-6 infection. The net reproductive rate (R[sub 0]) of covertly infected females was 50% lower for infected females compared to control mosquitoes, whereas non-infected exposed females had an R[sub 0] approximately 15% lower than that of controls. Reproduction caused a significant decrease of about 13 days in mosquito longevity compared to females that did not reproduce (P < 0.001). Infected females lived 5-8 days less than non-infected exposed females or controls, respectively (P = 0.028). Infected females and non-infected exposed females both had significantly shorter wings than control insects (P < 0.001). There was a significant positive correlation between wing length and longevity in covertly infected female mosquitoes but not in control or non-infected exposed mosquitoes. Longer lived females produced more eggs in all treatments. There were no significant correlations between body size and fecundity or the production of offspring. There was also no correlation between fecundity and fertility, suggesting that sperm inactivation was a more likely cause of decreased fertility in older mosquitoes than sperm depletion. We conclude that covert infection by iridescent virus is likely to reduce the vectorial capacity of this mosquito. [ABSTRACT FROM AUTHOR]

Abstract: The aetiology of large melanized inclusions occurring in the haemocoel of adults of some diprionid sawflies is not fully understood. Their occurrence has been associated with nuclear polyhedrosis virus (NPV), but also with extreme temperatures, parasitism, and prolonged diapause. High frequencies of inclusions are found most often during NPV epizootics. In laboratory experiments with Neodiprion sertifer larvae, ingestion of large doses of a common bacterium, Enterobacter cloacae, was shown to induce inclusions indistinguishable from those associated with NPV infection. It is argued that a bacterial aetiology is not contradicted by the other conditions reported to be associated with inclusions. The bacterial aetiology provides an explanation for the low frequencies of inclusions in N. sertifer populations with no NPV infection. It is proposed that the ability to form inclusions may have evolved as a defence against bacterial infection. [ABSTRACT FROM AUTHOR]

Summary Honey is one of the most important agricultural products for export in Argentina. In fact, more than 3.5 million beehives and 50 000 beekeepers are related with this production, mainly located in Buenos Aires province. Honeybee mortality is a serious problem that beekeepers in Argentina have had to face during the last 3 years. It is known that the consequence of the complex interactions between environmental and beekeeping parameters added to the effect of different disease agents such as viruses, bacteria, fungi and parasitic mites may result in a sudden collapse of the colony. In addition, multiple viral infections are frequently detected concomitantly in bee colonies. We describe here the preliminary results of a survey of three honeybee-pathogenic viruses, acute bee paralysis viruses (ABPV), chronic bee paralysis viruses (CBPV) and Sacbrood viruses (SBV) detected during a screening of 61 apiaries located in the main honey producer province using a RT-PCR assay. This is the first molecular report of the presence of these viruses in Argentine apiaries. [ABSTRACT FROM AUTHOR]