The neonicotinoid Clothianidin has a negative impact on NF-κB signaling and on immune responses controlled by this transcription factor, which can boost the proliferation of honey bee parasites and pathogens. This effect has been well documented for the replication of deformed wing virus (DWV) induced by Clothianidin in honey bees bearing an asymptomatic infection. Here, we conduct infestation experiments of treated bees to show that the immune-suppression exerted by Clothianidin is associated with an enhanced fertility of the parasitic mite Varroa destructor, as a possible consequence of a higher feeding efficiency. A conceptual model is proposed to describe the synergistic interactions among different stress agents acting on honey bees.

Honeybees use propolis collected from plants for coating the inner walls of their nest. This substance is also used as a natural antibiotic against microbial pathogens, similarly to many other animals exploiting natural products for self-medication. We carried out chemical analyses and laboratory bioassays to test if honeybees use propolis for social medication against their major ectoparasite:Varroa destructor. We found that propolis is applied to brood cells where it can affect the reproducing parasites, with a positive effect on honeybees and a potential impact onVarroapopulation. We conclude that propolis can be regarded as a natural pesticide used by the honeybee to limit a dangerous parasite. These findings significantly enlarge our understanding of behavioural immunity in animals and may have important implications for the management of the most important threat to honeybees worldwide.

While there is widespread concern regarding the impact of pesticides on honey bees, well-replicated field experiments, to date, have failed to provide clear insights on pesticide effects. Here, we adopt a systems biology approach to gain insights into the web of interactions amongst the factors influencing honey bee health. We put the focus on the properties of the system that depend upon its architecture and not on the strength, often unknown, of each single interaction. Then we test in vivo, on caged honey bees, the predictions derived from this modelling analysis. We show that the impact of toxic compounds on honey bee health can be shaped by the concurrent stressors affecting bees. We demonstrate that the immune-suppressive capacity of the widespread pathogen of bees, deformed wing virus, can introduce a critical positive feed-back loop in the system causing bistability, i.e., two stable equilibria. Therefore, honey bees under similar initial conditions can experience different consequences when exposed to the same stressor, including prolonged survival or premature death. The latter can generate an increased vulnerability of the hive to dwindling and collapse. Our conclusions reconcile contrasting field-testing outcomes and have important implications for the application of field studies to complex systems.

Several concurrent stress factors can impact honey bee health and colony stability. Although a satisfactory knowledge of the effect of almost every single factor is now available, a mechanistic understanding of the many possible interactions between stressors is still largely lacking. Here we studied, both at the individual and colony level, how honey bees are affected by concurrent exposure to cold and parasitic infection. We found that the parasitic mite Varroa destructor, further than increasing the natural mortality of bees, can induce an anorexia that reduces their capacity to thermoregulate and thus react to sub-optimal temperatures. This, in turn, could affect the collective response of the bee colony to cold temperatures aggravating the effect already observed at the individual level. These results highlight the important role that biotic factors can have by shaping the response to abiotic factors and the strategic need to consider the potential interactions between stressors at all levels of the biological organization to better understand their impact.

Inter-row management in vineyards can influence the abundance of grapevine pests and their natural enemies. In 2013–2015, in a vineyard in northeastern Italy, the influence of two vineyard inter-row management strategies (i.e., alternate mowing, AM, and periodical tillage, PT) on the population dynamics of grapevine leafhoppers Hebata vitis and Zygina rhamni and their natural enemies, the mymarid Anagrus atomus and spiders (Araneae), and other hymenopteran parasitoids, were studied with different survey approaches. The infestations of both leafhoppers were lower in AM than PT due to the reduced leafhopper oviposition and higher nymph mortality in AM. This occurred although leafhopper egg parasitization by A. atomus was greater in PT than AM according to a density-dependent relationship with the leafhopper egg amount. Hymenopteran parasitoids other than A. atomus were the most abundant in AM, probably due to the higher availability of nectar and pollen than in PM. The significantly higher population densities of hunting spiders in AM than PT can be associated with the higher predation of leafhopper nymphs. Therefore, the study demonstrated that the alternate mowing of vineyard inter-rows enhances the abundance of natural enemies, such as spiders and hymenopteran parasitoids, and can contribute to grapevine leafhopper pest control.

Bois noir (BN) is a grapevine yellows disease associated with ‘Candidatus Phytoplasma (Ca. P.) solani’ that is transmitted to grapevines by the planthopper Hyalesthes obsoletus Signoret which uses herbaceous plants such as Urtica dioica as a pathogen reservoir. Urtica dioica is often widespread along ditches bordering vineyards, and a gradient in decreasing BN symptomatic grapevines is observed from the vineyard edges facing these ditches. In two vineyards in north-eastern Italy, over eight or seven years, the ditch bordering one edge of each vineyard was divided into two sections; in one of these, U. dioica was chemically weeded in April, while the other one remained untreated. The impact of chemical weeding on the spatial distribution of both H. obsoletus captures and newly BN symptomatic grapevines was assessed. The reduction in H. obsoletus captures in the vineyard sector facing the section of the ditch subjected to weeding corresponded to a decrease in newly symptomatic grapevines. These findings demonstrated that nettle removal from areas surrounding vineyards can effectively control BN.