Biological control of the tick Ixodes ricinus by pathogens and invertebrates

In this chapter we will focus on the tick Ixodes ricinus, with its main geographical distribution in Europe. It is known to transmit a variety of pathogens, among them Borrelia burgdorferi sensu lato, the causative agent of Lyme borreliosis. Tick population control is one of the measures to reduce the incidence of tick-borne diseases. Due to non-target effects of chemical acaricides, acquired resistance against chemical acaricides and increased regulations, there is a demand for sustainable control measures that may be used in integrated vector management (IVM) of ticks. This chapter describes and evaluates the present knowledge on biological control of I. ricinus as an alternative to the use of chemical acaricides. Biological control makes use of living organisms (e.g. fungi, bacteria, nematodes, invertebrate predators, parasitoids) to suppress a pest population. The natural occurrence of these organisms in I. ricinus and the use of these organisms as biological control agents against I. ricinus are reviewed. Entomopathogenic fungi (Beauveria and Metarhizium spp.) are the most commonly used biocontrol agents against ticks. A variety of nematode species are also shown to be effective against different tick species, but the knowledge on the operational use of invertebrate predators and parasitoids to control ticks is limited. We conclude that there are several candidates for the biological control of ticks, but that the knowledge on the natural occurrence and efficacy of these to control I. ricinus populations is very limited. There is, therefore, a need of more studies on naturally occurring enemies of I. ricinus to be able to suggest possible biocontrol candidates. These candidates should be tested in controlled laboratory and field studies with the aim to develop elegant, precise and effective biocontrol strategies for the control of I. ricinus that may be used alone or in combination with other control strategies in IVM.