The European honeybee, Apis mellifera (EHB), is the world’s most important managed pollinator. Unfortunately, there has been a significant increase in the level of over-winter colony losses for EHB in many regions of the world in recent years, while agricultural demand for pollination services has been escalating, raising concerns for food security. Surveys have identified parasites and pathogens as primary contributory factors and that the ectoparasitic mite, Varroa destructor (varroa) and the viral diseases that it transmits, are key to EHB colony losses. Initially, in-hive use of was effective for varroa control but resistance rapidly developed. This is a major problem as there are few synthetic pesticides available that do not kill bees and current alternative measures are only partially effective. There is an urgent need for new control methods underpinned by fundamental knowledge to ensure their sustainable use.
In previous research, it was showed that varroa mites are susceptible to lethal infections by entomopathogenic fungi, which have potential to be used as biological control agents. A number of species of these fungi are available commercially for the control of insect and mite pests of crops, but their use against varroa is a novel idea. Infection occurs via the topical application of fungal conidia. Entomopathogenic fungi are considered to be low risk to people, and we have identified strains of fungi that infect varroa but do not kill EHB. However, there are knowledge gaps about how entomopathogenic fungi interact with varroa and bees and this is an impediment to commercialisation and use of a fungal control agent.
The aim of this project is to provide new information of the interactions of EHB, varroa and fungal biocontrol agents.
The project has three parts as follows:
i. Characterise the virulence of different strains and species of fungal pathogens against varroa and bees. A laboratory bioassay will be used to quantify the susceptibility of varroa mites, feeding on bee pupae and adult bees, to topical applications of a select number of fungal strains. Fungal virulence will be quantified in terms of lethal concentration of conidia suspensions, lethal dose (= conidia per mite) and time to death. The mode of action of fungal pathogens to varroa will be investigated including the pattern of deposition of conidia on the mite surface and the time required for conidia to germinate and penetrate varroa mites. Work will also be done to determine whether the candidate fungal strains have any sub-lethal impacts on bees.
ii. Quantify the effects of temperature on the activity of fungal pathogens. Bee colonies have relatively warm temperatures that can inhibit the activity of some fungal strains, so understanding the thermal biology of fungal control agents is an important area of study. In this part of the project, work will be done to determine the effect of temperature on fungal growth, conidia germination, infection and virulence. A simple model will then be produced to predict fungal speed of kill under different temperature regimes.
iii. Investigate the effects of fungal treatment on transmission and activation of bee pathogenic viruses by varroa. A key test of a fungal biocontrol agent of varroa will be whether it can reduce the impact of the harmful viruses that are vectored by varroa mites to bees. Experiments will be done to investigate the ability of fungal treatment to reduce the transmission of DWV from varroa to bees. We will also investigate the effects on fungal pathogens on the immune response of bees, specifically to determine whether any immune priming effects against fungi spill over into pathways associated with antiviral defences.
Dave dot Chandler at warwick dot ac dot uk