Varroa sensitive hygiene

About: Varroa sensitive hygiene is a research topic. Over the lifetime, 714 publications have been published within this topic receiving 24928 citations. The topic is also known as: VSH.

The effect of pathogens on honeybee learning and foraging behaviour

Abstract: The European honeybee, Apis mellifera, is important economically not just for honey production but also as a pollinator. Bee pollinated plants contribute towards one third of the food eaten worldwide. However, honeybee numbers in some areas are declining. A range of interacting factors are thought to be involved, including pathogens and parasites, loss of forage, pesticide use, bad weather, and limited genetic variability. Pathogens are also known to cause changes in the behaviour of their hosts and these premortality and sublethal effects of disease may well play a role in colony declines and are the focus of this thesis. For individual bees the fungus Metarhizium anisopliae was used as a model pathogen and RT-Q-PCR was used to detect and quantify naturally occurring pathogens. In field colonies the level of infestation of the parasitic mite Varroa destructor was modified as a surrogate for disease load as the amounts of many viruses correlate with mite levels. Survival experiments showed that both disease load and forage availability had an effect on honeybee longevity and feeding the bees pollen increased their survival. Learning experiments showed that both the fungus and some of the bees’ naturally occurring pathogens caused changes in the learning ability of young adult and older forager bees. Young adult bees were better able to learn when infected with the fungus, possibly because it made them more responsive to the sucrose stimulus, whilst older forager bees where less able to learn when infected with the fungus. Harmonic radar was used to show that honeybee flight ability was affected by naturally occurring pathogens, especially deformed wing virus which caused bees to fly shorter distances and for shorter amounts of time than uninfected bees. Observation hives were used to study in-hive behaviour showing that bees with more pathogens were likely to start foraging earlier than healthier bees.

Bacterially expressed dsRNA induces Varroa destructor gene knockdown by honey bee-mediated oral administration

Abstract: Abstract The ectoparasite Varroa destructor causes serious losses of Apis mellifera colonies and negatively impacts the beekeeping industry around the world. New control methods have been proposed based on the RNA interference technique. Previous reports showed that parasitized honey bees fed with double-stranded RNA (dsRNA) synthesized in vitro reduce the transcription levels of target genes in Varroa mites. An efficient and inexpensive alternative to produce dsRNA is the use of bacteria capable of achieving high levels of in vivo synthesis. In the present study, dsRNA synthetized in vivo was used to induce gene silencing in V. destructor and evaluate their effect on the survival of both honey bees and the parasitic Varroa mites. The results evidenced that dsRNA fed to the bees engendered gene silencing in mites, inhibiting expression levels of target genes by 50%. Indeed, a reduction of 50% in Varroa survival was observed when bacterially expressed dsRNAs were administered to mite-parasitized bees. Worker bees that were fed with Varroa-targeted dsRNA by oral route showed no survival differences compared to control bees, fed with sucrose or dsRNA-GFP solutions. Our results demonstrated that specific dsRNA over-expressed in bacteria is capable of reducing mite survival by bee-mediated oral administration. This study provides an efficient and low-cost method for dsRNA production to control parasites and honey bee diseases.

Bees and Pesticides

Abstract: Honey bees (Apis mellifera L.) are the main pollinating agents for numerous plants and fruit trees and hence, play a key role in agriculture and more generally in the maintenance of ecological biodiversity. They are mostly affected farm animals by pesticides. Indeed, pesticides work in two ways to reduce bee populations. First, many pesticides used in crop production are highly toxic to these social insects. Second, the use of herbicides can reduce the acreages of useful plants for the bee activity. Pesticides damages to honey bee colonies take different forms. Honey bees may be poisoned when they feed on nectar or pollen contaminated by pesticides. Bees may also be poisoned when they fly through a cloud of pesticide dust or spray or walk on treated parts of plant. Sometimes, colonies in the hives can be directly affected, but most commonly only field bees are killed or have their physiological functions altered. Toxicity and hazards of 158 pesticides to Apis and non-Apis bees are well reviewed in a study of Devillers et al. (2003). Honey and bee products have the image of being natural, healthy and clean. However, today bee products are produced in a environment, polluted by different sources of contamination. The contamination sources can be roughly divided into environmental and apicultural ones. Environmental contaminants are pesticides, heavy metals, bacteria, GMO and radioactivity, contaminants from beekeeping practice includes acaricides used for parasitic mites (mainly Varroa) control, bee repellents used at honey harvest, pesticides for wax moth and small hive beetle control and antibiotics used against foul brood disease. There are very few special residue limits for honey, making it difficult to discuss the toxicological importance of residues. Honey makes a minimal contribution to the acceptable daily intake (ADI) of pesticides. The most common insecticides that have been examined in European honeys include organochlorines, organophosphorous pesicides and carbamates. In a recent study using 50 honey samples from Spain and Portugal, residues of 42 different pesticides were examined (Blasco et al., 2003). Most of the pesticides found in honey were organochlorines. Among them, gamma-HCH was found in 50% of the samples and was the most frequently detected substance, followed by HCB in 32% of the samples and other isomers of HCH. The values found varied between 0,03 and 4,31 mg/kg, but most of them were bellow 0,5 mg/kg. There are several other European studies with no measurable residues of insecticides in honey found above the detection limit, which varied between 0,005 and 0,050 mg/kg. (Bogdanov, 2006). Similar situation is in Slovakia, monitoring of 20 honey samples for the presence of 14 insecticides showed no detectable residues of insecticides (see the presentation). The effect of imidacloprid (known under the name of Gaucho) on bee health is highly controversial, even just very small residues were found in honey. (Bogdanov, 2006). SUMMARY